/ohm/

>>891543

anyone have experience using photo Interrupters?

how accurate could this one be if i was to program a microcontroller to count the interrupts to determine a motor's position?

https://www.sparkfun.com/products/9299

What happened to our OP?
We used to have a pastebin.

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>>891543
I am trying to compile a shopping cart of components for the matchless metal detector found here: http://www.geotech1.com/pages/metdet/projects/matchless/matchless150c.pdf

Can someone look over it and let me know if it looks good? I wasn't too sure about the following:

14 pin DIL IC socket (I could only find exact on ebay for ~$17)
ICM7556IPD (Ebay)
BC549C(Again, could only find on ebay)
.01uf ceramic disc (listed as 50v, will this work?)
500ohm pot in place of 470ohm

Couldn't find:
.001uf resistor polystrene (Does it have to be poly?)

I forgot:
A switch

My cart contains a CMOS 1555 and a 14 PIN IC Socket which I thought might work instead, truthfully I have no idea what I am doing. Do I need the components from ebay? Are there any US based companies anyone knows that stock these?

I did some electronics work back in highschool and I am fairly confident I can limp through online schematics enough to enjoy some things I can build that may be out of my price range on my salary. I am willing to learn, any suggestions helpful.

Anyone familiar with AVR microcontrollers? I'm doing this job for a friend where I'm migrating some PWM frequency and phase correct code from an Atmega128 to an atmega2560.

Never done mcu programming before - I do applications dev - and am wondering where in the world the code would change.

Just looking for a place to start.

>>891614

0.001 uf resistor

uhh what

>>891547

Depends on the number of counts on your encoder wheel. Most are like 24-36 PPR (pulses per revolution).

Also, that one wouldn't work for keeping position unless you were absolutely sure the shaft could never rotate backwards.


Actual, high-resolution optical encoders bottom out a few hundred PPR, and go up well into the thousands. They're much more expensive, though. Total overkill if you don't need accuracy measured in arc minutes.

>>891623
Its right there on the components list on the left from the schematic.

.001uf polystyrene capacitor

What's the problem?

>>891626
On the right rather.

Guys. Dumb question, please bear with me. How do I calculate the power requirement of multiple things? I'm building a Daft Punk helmet. I have an LED matrix board with a working voltage of 2.4 - 5.5v, 256 clear red leds, two led chaser circuits with 8 white leds each.

How do I calculate the power required? Therefore, how do I determine what type of batteries I should use?

>>891614
>14 pin DIL IC socket (I could only find exact on ebay for ~$17)
Try again. Or omit altogether if you're desperate.
>CMOS 1555
Your circuit uses a dual timer, 7556. If you substitute it with 7555, you need to change the circuit a bit. Other CMOS 7556s should work, unless the design seriously sucks.
>BC549C(Again, could only find on ebay)
Any decent store should have that, but you can most likely substitute BC547C or 2N3904.
>.01uf ceramic disc (listed as 50v, will this work?)
Yes.
>>891626
The fact that you wrote "resistor".
Polystyrene capacitors are bit unusual, but you can try a 1nF ceramic NP0 capacitor instead. Or polypropene.

>Are there any US based companies anyone knows that stock these?
Yeah, Digikey being one of the best known.

>>891586
/ohm/ died at one point and the link was lost. Dunno if we still have an archive.

>>891637
You need to know currents as well.
Basically you figure out the suitable voltage for all your stuff. You might need to add regulators to make them all work from the same voltage. (Or you can use multiple battery packs with different voltages, but it's quite inconvenient.) The voltage must be something available from batteries. Like 3.6V for 3 x NiMH. If it's not, you need more regulators.
Then you sum all the currents together. Note that if you use switching regulators, the input current is different from output current. Then you determine the desired working time in hours and multiply it with the load current and that's your minimum battery capacity in mAh or Ah.

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Hi guys, im the LED guy from few days back.
Let me rephrase my question.
Lets say I have LED diode module, and its data sheet says:
If - Forward Current: 9 A
Vf - Forward Voltage: 3.6 V.

Can I connect four of them as pic related?
I have power supply that says:
Variable Output Voltage 1-16 VDC
Variable Output Current 0-60 A

Its one of those laboratory power supply, so It has current limitation (i think).

If I connect my supply and those LED as pic related and set my power supply to limit current output as 18 A do I even need a resistor?

Thanks a lot.

>>891648
Troll whizzard is troll.
Yes, you can connect them that way, but since the PSU can supply 16V, connecting them all in series would be easier and produces better results.
>do I even need a resistor
With suitable definition of "need", no.
It's good to be there, but considering the current and LED voltages, your wiring might have enough resistance to even the things out.

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>>891652
So like this?
and set my power supply at 14.4 V and 9A.
Why is it better to connect them at series?

>>891654
Yeah, that way, and you don't need the resistor now, since there's no need to balance anything. Just the the PSU to supply 9A.
Better, because now all the LEDs automatically run at the same current.

>>891655
*set the

>>891655
So I dont even need supply with such high current output right? I can use power supply with 10A max output?

Im not electrical engineer, im into chemistry, and I always thought that more devices in the circuit means more current needed.

So if I connect those in series I need higher voltage but just 9 amps. And if I connect them parallel i need lower voltage but more current?

We were going to buy that power supply.
Should we buy this one (16V/60A) or something else (32V/30A)

>>891648

that is one very retarded calculator. if you have 9 amps going thru a 1 ohm resistor, that causes a voltage drop of 9 volts. yet your power source is only 7.2V. does not compute!

i've never trusted online LED calculators coz they dont do a sanity check on the results. now, i see they can be just downright wrong.

> set my power supply to limit current output as 18 A do I even need a resistor?

if you have a parallel circuit, then the current limit wont do what it's supposed to, coz you could have 18A going thru one branch and 0A going thru the other. but if you have a 4-diode series circuit, with limit at 9A, all is protected. better yet, make it 7 Amps, you dont want to be at the very edge of destruction.

anyway, if you absolutely want to use the 2x2 circuit, a proper calculation follows:

assuming a 10V supply, and 7A current, you'd need a 0.4-ohm resistor at 25W or better.
R=(10v-3.6v-3.6v)/7a=0.4ohm,
P=(10v-3.6v-3.6v)*7a=19W

>>891658
4 x yes
As long as you don't need so many LEDs that the total supply voltage becomes a problem, it's more convenient to connect them in series and use higher voltage, lower current PSU.
Btw, it would be a good idea to add overvoltage and reverse voltage protection diodes in parallel with each LED to protect them from random spikes. 4.7V zener diodes should work.

How do I sensor a sensorless bldc and interface it with a motor controller?

>>891660
>that is one very retarded calculator. if you have 9 amps going thru a 1 ohm resistor, that causes a voltage drop of 9 volts. yet your power source is only 7.2V. does not compute!
TBF, he did tell it that that source voltage was 7.2v, the forward voltage was 3.6v, and there were two LEDs, leading to a voltage across the resistor of 0v.

Garbage in, garbage out.

>>891622
It depends on what the code does exactly. The biggest differences would be the pinout and baud rate. Some libraries might not work either, if you're including any. I'd have to see the code to know for sure though.

Incoming with small stupid question related to /ohm/.

PWM output voltage on micros is usually (0, Vcc), right? I can expect that if I supply my chosen micro 5V then the PWM signal with duty cycle of 100% will be ever so close to 5V? Or will there be some losses that have to be compensated for with external circuitry?

>>891780
For what i know PWM is usually done by using transistors, which have some voltage drop like a diode.

>>891642
I really appreciate the help with this. You're right I did mistype resistor, I didn't notice.

In regards to the 14 PIN DIL IC socket; Truth be told on the schematic it's listed as optional. Due to my limited knowledge of electronics, I don't know under what criteria could this be optional. I figured I should just get everything listed, and not modify things if I can prevent it.

The dual CMOS I see listed exactly as such on the schematic, and also listed as (no substitutes). As I was typing my previous post last night I had the chance to google and look into things further, and understood that what I had placed in the cart more than likely was not proper. I compiled that shopping cart on my phone at work, which makes it difficult to jump around through browser tabs researching.

What reference were you using to come up with an alternative to my missing capacitor? I'd like to be able to do the same as well.

I will build the cart again at Digikey and post a screen later tonight after work. Thanks again man.

>>891771
https://www.dropbox.com/s/bdb31wshfrzooc8/Atmel128Code.zip?dl=0

That's the code. The guy is handicapped and the guy who wrote the original software passed away not too long ago.

>>891796
The DIL IC socket is just there so you don't damage the IC while soldering it. You can solder the socket in your circuit and then just plug your IC in later.

As for your capacitor, I'm not the guy you are replying to, but really small valued capacitors like the ones you are asking aren't very common. There's really only a few types of those.

Are people here familiar with Labview?

>>891835
Don't you have to pay for that shit?

>>891838
not if your uni has a license

...or if you sail the seven seas

>>891839
fuck my cheap ass uni then

Any of you guys used the reflowster? I'm looking into a DIY toaster oven reflow setup but idk what the best controller is these days.

>>891624

That makes sense. thanks

I bought an Adafruit arduino motor shield where you can change the step mode electronically. Sparkfun has a similar product, and I've found a couple others online as well. These are all little single-chip drivers, bigger than the ones for 3D printers but still pretty small power capacities.

The Adafruit shield wasn't very big so I switched to bigger and bigger (cheaper Chinese) motors+drives. I'd like to have that feature but none of the larger stepper drivers have it; at times I want motors to run faster but other times I want it to move slowly with great precision.... None of the bigger ones can switch their modes electronically--they all have DIP switches to change the microstep mode. (also the power usually has to be off)

Are there any bigger stepper drives that can do this?... I am looking at China-price-level drives, and I'm running nema 34 motors at 60v and around 4 amps peak.

I also know that it would prolly be possible to alter some DIP drives to be controlled by an arduino or whatever (with a relay for controlling the driver's power) but it seems a useful feature and I'm surprised that no larger drives seem to include it.

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Tested our PCB for the LME49830 datasheet amplifier circuit today and the results were surprisingly good considering this was my first serious PCB design and I was expecting some fatal flaw - there was next to no DC offset (DMM measured 0.1mV) and everything works fine. The oscilloscope in the pic shows the output for a 0.5V amplitude 1kHz sine at the input.

>>891923

why not just replace the dip switch with a transistor connected to your microcontroller

>>891923

Every single chip can have its microstepping mode changed elctronically. All the DIP switch is is a pull down or pull up connected to the relevant pins. The exact same thing can be done just by connecting a couple output pins on your microcontroller to the microstep select pins on the driver. (Note that the datasheet usually stipulates that the output enable pin, if the driver has one, should be driven such that the outputs are disabled when you change settings.)

The reason you never see anything other than DIP switches is because there's almost never any reason to do this. I say almost never just to be safe; I can't think of any reason you'd want to change step settings on the fly unless there was some really weird-ass limitation with the circuitry generating the step pulses. If you want it to go fast, just clock the step line faster.

>>891835
My uni has a license so I know a tiny amount

>>891796
The socket is there so that you don't need to solder the IC. It's bit safer that way. You can also easily replace or remove the socketed IC later. So basically it's there just for convenience.
>The dual CMOS I see listed exactly as such on the schematic, and also listed as (no substitutes)
The main thing with 7556 is that it is a CMOS chip, while the original 556 is bipolar. This is big enough difference to matter. It is easier to say "DO NOT SUBSTITUTE" than make a list of allowed substitutes. That said, there's a small chance that the design really needs the exact chip to work.
>What reference were you using to come up with an alternative to my missing capacitor?
Polystyrene capacitors are used in situations where high stability or low losses are important. NP0 ceramic has nominally zero temperature coefficient and low losses. Polypropylene has smallish negative temperature coefficient and low losses. Polystyrene also has a small negative tempco.

Would a TDA amplifier suit my purpose if im just trying to make a really basic portable speaker set. Speakers are 6W @ 8 ohms. I don't really want to mess with much amplifier design so I would figured this would be the easiest route. Also would I put a 12W heat sink on to account for both speakers? Thanks

>>892240
yep. there's probably a modern digital alternative that's less hot and more efficient, but a tda2005 will git'r done with a handful of passives.

>I'm new to electronics, where do I get started?
There are several good books and YouTube channels that are commonly recommended for beginners and those wanting to learn more, many with advanced techniques. The best way to get involved in electronics is just to make stuff. Don't be afraid to get your hands dirty.

>Links to get started
http://pastebin.com/9UgLjyND

use the archive you stupid noobs
https://warosu.org/diy/?task=search2&ghost=yes&search_text=&search_subject=%2Fohm%2F&search_username=&search_tripcode=&search_email=&search_filename=&search_datefrom=&search_dateto=&search_op=op&search_del=dontcare&search_int=dontcare&search_ord=new&search_capcode=all&search_res=post

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bald dodododo

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what do you call these types of connectors? i need to buy various male/female ones.

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r8 my scope (Sencore PS 163)

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>>892702

>>892571
Dunno if they have any more special name than "header" and "housing". The male part looks like normal 0.1" pin headers with a shrink wrap shroud.

>>892571

DuPont connectors.

Do yourself a favor, though, and buy the legit crimping tools for them. Plain ones don't work at all, and the shitty cheap ones are actually just generic, small-connector crimpers that happen to have a profile that can be made to work with DuPont terminations. They'll grip the insulation on the wire, but won't crimp properly around the wire itself.

Proper crimpers have a stepped set of jaws, with the forward teeth having smaller gaps to crimp the wire itself.

Not my pic, but the shitty crimping tool I have. Terminals are hard to load into the jaws and you have to solder the wire in afterward to ensure proper contact. Makes things take literally 4-5x longer per terminal than a decent crimper would.

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>>892719

Herp derp pic related.

Will an electronic 'lock' (not really safe i think but it will look cool) project using a PIC, a keypad and an LCD function well with an oscilating circuit of 32 khz? (LP)
I have never gone past simulation but i'm not sure what frequency i should use since it will run on batteries and i don't want it to drain them, i'm having a hard time finding a 200 khz crystal

>>893334

Unless you're interfacing with something with a set bitrate or you actually need the clock cycles for something (lots of computation or ADC sampling), the frequency is pretty arbitrary. Use whatever.

>>893334
Depends on details. For example, if you're using an LCD module instead of a dumb display, updating the display consumes very little CPU power.
On the other hand, if you have a dumb display (you wanted low power consumption) which requires you to feed it with 50Hz or so AC and you're using the controller to generate it, then you need an interrupt going off every 80 machine cycles or careful cycle-counting in order to avoid DC component in output waveform. This can be annoying/tedious depending on the rest of the program.
Same thing with the keyboard. Matrix keyboard needs scanning at a reasonable rate to not miss key presses, while a bunch of individually connected keys needs less processor power.
And like the other anon said, obviously things like a serial port running at 9600bps won't be possible.

Tl;dr. Doable with 32kHz clock, easiness depends on details.

>>893355
Can you give me the name of the subject about the interrupt thingy?
PS Since it's doable I'll buy the stuff and breadboard it , it's dirt cheap anyways

>>892721
Goddamnit I could have used this today.

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I scrapped this temperature sensor from a computer case. Having no data-sheet, I'm not sure about its calibration. I tried to put it between my fingers, adding a medical thermometer just beside, made the difference between them and added this difference to my algorithm.
I plan to check on some ice and then apply some dichotomy between high and low.

How would you do it ?

>>893409
Info about the drive requirements of dumb lcds: google "driving static lcd"
Info about PIC's interrupts: "pic interrupt tutorial" + datasheet.

If you ignore the AC drive requirement, the display is (very) slowly ruined.
How you exactly set up interrupts depends on various things, but the basic idea is to set a timer to generate periodic interrupts (for example, timer0 can generate overflow interrupts), enable the interrupts (global and peripheral-specific) and then hook your service routine to the interrupt vector. The service routine has to save all the relevant registers (like w and status) and restore them on return, or the main program gets fucked. If you're using C, the compiler does the save/restore thing for you and hooks the function properly, if you tell it that the function in question is an ISR. Better check the code it produces to see it isn't excessively long, though. You have to return from interrupt as soon as possible.

There are also PICs with integrated LCD drivers which (probably, never used them) would do the AC drive thing for you. There are also separate driver chips.

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I am the poster from >>891614 & >>891796 and I have returned with my updated supplies list. As before I was hoping someone might be able to look it over and let me know if everything is as requested on the schematic.

Shopping cart-
http://www.digikey.com/short/t502wf

Matchless Metal Locator schematic -
http://www.geotech1.com/pages/metdet/projects/matchless/matchless150c.pdf

I also added to my cart an Adafruit Perma Proto board. I'm real hobbiest level and just trying to make a quality product. Is this a good choice for a project like this?

>>893464
Thanks m9

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Sup /ohm/.

I've searched around the internet for about a week now trying to find details on what causes pic related..


Description:

>power on
>vertical lines down most of the screen
>horizontal lines ~1/4 inch from the top of the screen
>as the monitor warms up, the lines dissappear, but the horizontal ones dont


I think it may be bad capacitors on the power circuitry, but I want /ohm/s advice before tearing them out and replacing.


Anyone?

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I got these two thermoelectric Peltier modules. They are old but they still seem functional. I tested them with low voltage and the other side cools down and the other side gets warm. Any ideas for projects or experiments that I could do with these devices?

>>893602
Tear down an old cd drive, mount them in there with apropriate heatsinks and fans. In the end pc will use that cooler air than normal room temp to cool things so it will run cooler.

>>893599
just open them already and have a peak, VERY CAREFULL when opening the front, the plastic has tabs and no matter what you do dont use the lcd as place to pry with your screwdriver, better ruin the frame a bit on the outside

>>893431
Put the thermistor somewhere where its 25c and measure its resistance, then you end up knowing if its a 10k thermistor etc. The change in resistance is non linear so you really need an algorithm.
This is the place to start http://playground.arduino.cc/ComponentLib/Thermistor

>>892571
>>892719
Unless you're going to do hundreds fuck spending alot of money on a crimp tool, just solder and crimp with normal pliers, but i guess if you have money to throw around sure

>>893658
Opened up without any hassle.

I think it's the inverter board.

When I apply power to the inverter without attaching it to anything.... then attaching the cable the picture pops up on the LCD as if it's been on for some time.

The problem is ... I can get the damn screw out of the inverter board to flip it over look at the caps.

kek.

>>893672
why cant you get it out ? if its chewed up just use pliers or cut a slot for - screwdrivers in it

>>893674
No no, nothing that complicated.

All I have is a shitty mini screwdriver with a girth similar to a mouse penis.

My ratcheted driver set is about 150 miles away.

I need to get a new one anyway. When I've opened it up I'll take a look at the caps. I have a feeling Its the inverter board .... I'll post pics to get /ohm/s opinion tomorrow.

Will someone please look over my shopping cart before I place the order? >>893470

Only posting because thread is currently active and I require assistance!

>>893689
do you really need the 7$ dial ? find something cheapper
also 9v battery clip can be made by disassemble of old 9v battery and using the top

>>893689
also if you wana save tons of money, order shit from ebay from china before you actually need it, so u build up a stock of items, those proto boards are so expensive on digi. Also from the looks of the cart, every items is just 1 quantity, u deff want more since likely some parts will break in assembly

>>893692
The dials are aluminum and have numbers on them. They are $3.72/ea and it's nice they have numbers and are durable seeing as how it's a metal detector. I don't have an old 9v around, so snap lead it is! Thank you.

>>893664
ok thank I will try it

>>893658
>>893672
>>893674
>>893686


Opened up.

Caps look fine tbh, none obviously bulging.... none leaning either. The bottom bungs looks intact.

any ideas?

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>>894182
anus.

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Sup /ohm/? Maybe you have some ideas for this:

I have a set design I'm helping a friend with. The lights on this set are controlled by DMX dimmers. These dimmers just have an incandescent lamp style triac output which is fine, because we're using incandescent lamps. the set starts dark and then a fake "generator" starts and kicks the lights on. The lights will them dim and brighten in time to "generator" sounds playing in the background.

I have a "TV" that I want to come on when the generator starts. The TV is actually a raspberry pi and computer monitor and they are connected to regular 120V power that is always on. My plan is to have the pi show a blank screen and then an input will trigger it to play an actual video when the "generator" "turns on", as if the TV had just received power. My first thought was to use a relay with a 120V coil, connect that to the output of the DMX dimmer, and use the relay contacts to trigger the pi to play my video. I only need the relay to trigger momentarily, but I think the choppy waveform coming out of the dimmer would wreak havoc on the relay coil eventually, even if it did manage to trigger it at first. Pic is that circuit.

Could I rectify the chopped output of the dimmer and use that to trigger a relay with a DC coil? Any other bright suggestions? Thanks.

>>893670
>Unless you're going to do hundreds fuck spending alot of money on a crimp tool, just solder and crimp with normal pliers, but i guess if you have money to throw around sure

The thing about 0.1" connectors is that they're used fucking _everywhere_ . They are the de-facto "generic" interconnect, and, because of this, they're by far cheaper than any other kind of connector you can buy.

Which means, in turn, if you're an electronics hobbyist (as opposed to some guy just needing a few to repair whatever), you're going to be using them a lot, simply because they're cheap and work for pretty much anything under 1A. Look, I'm the biggest tightwad you'll ever meet, but holy shit trying to crimp and solder these things without the right tool is so much more of a pain in the ass than I'm willing to deal with. Or at least more than I'm willing to deal with as often as I do.

Totally worth the $30 or whatever if you're going to be using these on the regular.

>>894199
power monitor via dmx

>>894232
Won't work. I can't have the stupid "LG" symbol display when the monitor starts up.

Looks like we have an extra DMX channel though so I will just set that to 100% on and use that for my relay coil. I'd still be interested in other ideas, though since using the extra DMX channel requires pulling a bunch more wire.

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>>892721
quick question. /o/ here. could you use the DuPont crimpers for ecu pins? looks like the same wire clamps but just a different shaped pin reciever.

>>894245
sucks. you cant find an old style tv monitor? so much simpler

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guys please help me i am copying this https://classcblog.files.wordpress.com/2015/07/esquematico1.png i dont know what im doing wrong, the stransformer is 220v to 24v, since in the diagram it using 1k resistance i swaped it to 680 since it was made for a 34v 1a transformer and i am using 24v1a

>>894270
the 4700uf capacitor is what im taking about just to clarify, this is the page i used https://classcblog.wordpress.com/2015/07/17/fuente-simetrica-variable/#more-10

>>894270
Capacitor flipped? Bridge rotated? Transformer connected incorrectly?

>>894274
i uploaded pictures of everything here http://imgur.com/a/h9bSn if u could help me, im kinda new to this i have no why its wrong

>>891543

Can I measure the inductance of a coil with only a multimeter?

Alternatively, do any lab equipment manufacturers accept food stamps?

>>894314
>Can I measure the inductance of a coil with only a multimeter?

Not unless it has an inductance measurement function.

And, no, they don't, smartass.

>>894314
>>894325

yes you can

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>>894314

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/ohm/ doesn't have a sticky?

What's some good literature or videos to learn about electronics. I do a lot of electronic work but I don't really understand it. Pretty much mastered soldering by this point, a lot of the work I do is buying the pieces and following instructions exactly, or replacing parts or leds or making my own usb/audio cables.

>>894338
Not very relevant with typical inductors used in electronics.

>>894461
See >>892275.
I thought our archive died, but apparently not.

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>>891543
I guess this is the beat place to post this... But me and my friend are going to build a gaming capsule like the Gimini Space Capsule. We have a sort of plan (mostly I do) about putting them side by side like pic related, and having large screens in front of the person.

But how should I go about this? And what material should I make it out of? Also, how to electronics on this thing to make it have wifi, and have both consoles be able to connect via wired?

Alot of help would be appreciated, as I a newb at doing /diy/ related stuff.

>>894496
We had a guy who made something similar. Search the archive for battlemech.
IIRC he used plywood for the outer frame.

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>>894496
So you aren't starting with any sort of starting point like an old cockpit or something? What's your budget?

Where's it going to sit? The wiring could be as simple as running an extension lead with a power board on it to power everything

Is pic related the sort of thing?

>>894503
Nope, just from the ground up.

And as for the budget, its like bare minimal that we can get out of it. Not 10,000, but not 1000.

And, sort of like your pic related, except enclosed for the most parts, and standing upright so your back is pretty much facing downward

>>894514
Do you want flat surfaces and hard edges or more organic shapes? hard edges = plywood like that anon said, organic shapes = plywood then fill it with some sort foam (expanding or not) then shape it and coat it in something harder.

>>894515
Hmm, well the Gemini had a rounded body, but I could make it octagonal of sorts...how would one work with aluminum?

>>894518
If you're new to diy then welding aluminum might be out of your reach, it'd be the strongest option but bolts or rivets would work too. sheets of aluminum are pretty expensive in most countries. Iron and steel can be welded by novices with a stick welder (the cheapest welding option) after an afternoons practice but it's much heavier. Maybe scrap iron sheeting if you can find it anywhere. Or you could think about a wooden frame with plasterboard sheeting, or plywood sheeting.

>>894522
Usually a good idea to draw up some plans before you buy anything, sketchup or blender are two free programs that work just fine for most basic projects.

>>894522
>>894525
Sweet, ill keep that in mind. Thanks alot /diy/

>>894266
Since I already modded a REALLY old TV for the monitor to sit in and it looks great, I'll just bite the bullet and pull that extra wire. Thanks though.

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>>894199
You use a DPST and use the other terminals to bring a constant DC voltage to the coil. That way the relay is latching and won't turn on/off at 50Hz.

Also probably a good idea to use a few diodes so there won't be any surprises.

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>>894256

Couldn't say for sure, but I'd bet they would. Crimp connections all work pretty much the same way (save for a few odd/proprietary ones), so as long as you have the right size tool, it should work.

Also they look almost identical to the terminals I have.

>>894183
Try hitting the caps around the t-con IC (TSUMU58EHJ) with some heat or cold (hair dryer, deodorant upsidedown etc). If they start passing too much AC to the IC, shits tends to get funky. A rapid temperature change will point out the dodgy one - the picture will unfuck itself.

Or get a cap with a similar or larger voltage rating and touch its leads to the existing one's. Observe polarity. Adding capacitance to a fucky cap will also result in a change in the picture.

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>>894690
Interesting. So you're saying that the cap may still be fucked without it being visibly bulged/leaking fluid. I suppose that makes sense.

I was reading some forum posts on 'badcaps' with a guy with the same product and similar picture issues. One of the replies was 'the Tcon is bonded to the panel' - which confused the shit out of me given that I'd assumed the TSUMU58EHJ was the t-con.

http://www.badcaps.net/forum/showthread.php?t=30365


Anyway, thanks for the help, I'll do exactly as you describe.

>>894711
Just to be clear. That image I just posted is a screencap of two of the attachments in that forum post I linked - not my own screen.

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>>894623
Thanks anon - good to know for future projects. I already pulled the extra wire to do >>894245
though, so imma roll with that plan.

>>891791
You have no idea what you're talking about.
>>891780
Yes. Make sure that you can get 100% duty cycle.

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I'm building an amplifier.
Rather than soldering the 5 different boards together, I want to have some sort of plug/jack setup.
Currently looking at the Molex Mini-fit Jr series.
Can anyone speak for or against them, or maybe recommend something better?

>>894711
Well the IC that's bonded to the panel rarely fails. Personally I've never seen one go. Its much more common for the ribbon cables to come loose either on the glass side or the pcb side. You have to be careful with those, they are not durable at all.

But yes, physically tiny electrolytics don't tend to bulge up, they just dry out from the seal around the leads going bad. That's why you shouldn't bend leads right at the component and heat short leads for very long.

>>894921
So. I heated and cooled but it didn't really make a difference, as far as I could tell.

What I then did was take a 6v battery pack, charged the caps, took my multimeter, and measured to check if there's a voltage.

All the caps are rated for 16v - 50v and range between 10uF to about 100uF ...one is 4.7uF.

I've found two that hold no charge whatsoever, as far as I can tell.

I also tested with similar valued caps In my stock cupboard to see if it was just my multimeter fucking up.

I replaced one. It made no difference to the picture, but I chopped up the one removed from the board out of interest. It seemed suspiciously dry, but at that scale I'm not sure if that correlates with anything. There would be barely any electrolyte in it anyway.

I'll replace the other and see if it makes any difference.

Hey ohm, I am not necessarily new to electronics and building shit, my problem comes from that normally I am following a guide but now I am working on my first full DIY project and don't know what to look for. I am making a chronograph with a force sensitive resistor at the end for a nerd gun that my friend is paying me to make. I know I need the resistor, infrared emitters and recievers, a micro controller (to calculate the Fps and impact), and a display. So my immediate questions are which micro controllers would be best suited for this? And what type of display shows the most promise for this concept?

>>894802

These are good for power and I'm using these for some of my projects, but for RF and audio you might want to use dedicated connectors. BNC maybe?

>>895049
These are fine for audio.

>>895000
If you're charging them in circuit, they would most likely dump all charge into circuit ground. So thats not a good way to check em.

Try putting a cap in parallel with each one on a live circuit and observe if there's a difference. (touch leads, polarity is important or you get sparks.)

The two caps next to the crystal will most likely make a difference, not necessarily in a good way. They're there for crystal compensation and have to have the correct capacity to work. Changing that changes the crystal frequency somewhat and will make either the IC shut down or corrupt the display even more. (Which coincidentally might be what's going on now. Caps gone, frequency off, picture garbled.)

>>891586
>>891642
http://pastebin.com/9UgLjyND

Is this it?

>>895169
Ah ok, will do.

I was looking for another method because the board is mounted really fucking awkwardly when online - I'll just suck it up.

Thank you for your continued help.

>>895049
>>895051
Cool guys, I guess that settles it.
Thanks.

Well /ohm/, we've officially existed for a full year. Happy birthday!

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Are snubberless, hi-com triacs like BTA12-600BW really safe to use without the snubber? I just noticed that the snubber still allows a small amount of current to flow through the load, even if the triac is turned off. In practice this means that the air pump in my hydroponic setup never really turns off.

>>895538
>safe
It's more about them working correctly. If you're worried about overvoltages, use a varistor or TVS.
That said, are you really sure it's the snubber leakage (<1mA) which keeps the pump running?

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>>895548

Isn't it more like 380 miliamps, since the resistor I've used is a 330R one? The pump is a 1 watt pump. It runs very weakly, but still runs. I've opened it, it's basically a small electromagnet (so it's an inductive load) that makes an arm squeeze a tiny bellows. The leaked current isn't enough to power on the lights or the fogger I'm using for the seedling bucket, but I see how it could make the pump run, albeit not at full power.

Can the inductive turn-off spike interfere with the mcu even if it does not cause the triac to false-trigger, since both the triacs and the 9V psu used for the microcontroller are being powered by the same outlet?

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Is it possible to solder the tab of a 7805 to the copper on a PCB without killing it?

>>895550
>Isn't it more like 380 miliamps
That 10nF capacitor dominates your snubber's impedance at 50Hz, but if it's a 1W pump, then 1mA certainly might be enough to run it.
Idjit tier solution: bypass the pump with a bigger capacitor, like 100nF.
Idjit 2: use a relay.

>Can the inductive turn-off spike interfere with the mcu
Depends, but assuming your design isn't shit, I don't think so.

>>895556
Yes. There are also several package variants which are specifically designed that in mind.

>>895558
>bigger capacitor, like 100nF

I'm using a 100nF x 1600v capacitor

>>895560
That's your snubber capacitor? It leaks 10 times more than the suggested 10nF capacitor. Use a smaller capacitor.
Also, I meant that you connect the 100nF capacitor across the pump so that it shunts the snubber leakage current (partially).

>>895561

Wait wait, how do I know how much current a capacitor will leak in a RC snubber?

>>895562
Capacitive reactance at frequency f: Xc = 1/(2*pi*f*C). Current is then I = V/Xc.
Btw, 100nF might resonate with your pump, so in addition to using smaller snubber capacitor, it might be required to use different value in parallel with the pump.

>>895565

1 / (2*PI*60*(100 * 10^-9)) = 26525 ohm

127v / 26525 ohm = 0.0047a

0.0047a * 127v = 0.5969W

Is that right? So, the snubber is actually providing the pump with more than half the power it needs?

>>895576
Yeah. Well ok, there are complications since the pump is reactive (Xl = 2*pi*f*L) and shit, but that gives a reasonably good idea of the leakage.

>>895580

If I knew the pump inductance, would I be able to pick a proper value for the snubber capacitor? What if I wanted the circuit to work for different pumps?

>>895586
That and the TRIAC's ratings would allow you to optimize it, but there's no reason to go that far in a circuit like this. The optimal snubber would be truly optimal for only one type of pump, which is also a reason to not optimize it that much.
What I really meant is that the capacitors and the pump form a resonant circuit and if the values happen to be right (resonance at 60Hz), the pump runs at higher power than expected.

Here's Fairchild's take on snubber design: https://www.fairchildsemi.com/application-notes/AN/AN-3008.pd

>>895590
So my best bet so far is to get rid of the snubber and just use a snubberless triac?

>>895593
If it were my design, I would try things in this order:
1. try smaller snubber capacitor
2. try removing the snubber altogether
3. if I happened to have snubberless triacs, I'd try it now
4. reinstall snubber, try shunt capacitor on pump, see if the pump is happy with it
5. consider relay
6. if I didn't have any snubberless triacs, I'd buy and try them now

>>895601

I think I'll have to just swap the capacitor for a smaller one. I'm using an optocoupler, so even if the triac is of snubberless design, the optocoupler will need a snubber, right?

Does anyone know what kind of sensor I should look for to calculate a short burst of force like the impact force of a flick of the finger? Someone earlier mentioned force sensitive resistors but those seem to measure pressure and dont seem to accurate or able to measure quick forces. Am I wrong? Or is there a better sensor for this?

>>891648
Assume a 0.7V drop on every LED and solve the currents and voltages in your circuit with your knowledge of ohm's law

>>891654
Falstad circuit calculator. Best thing for solving easy circuits quickly

>>895610
Right, you have an optotriac. Yeah, but at least you aren't forced to put it in parallel with the main triac. The Fairchild AN has some examples.

>>895649
Piezo sensor would be a popular choice.

>>895664
Is there a difference between a piezo sensor and the force sensitive resistor? It seems similar with just different wording. Also will any piezo sensor work or is there a specific variation like vibration or such?

>>895703
https://en.wikipedia.org/wiki/Piezoelectricity

Dunno what you mean by "specific variation like vibration", but you can get them in many sizes and shapes, with different sensitivities, capacitances, force and frequency ranges. The basic idea is still the same, force produces charge.

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>>891543

Crosspost - please help /diy/ friends!

Bought a winter beater 2003 Ford Focus and went to drive it the other day after letting it sit for 1-2 months. Battery was completely dead. Yesterday, my brother jumped it with my car and it ran fine off the Alternator power.

We drove it for maybe 10 minutes and that was enough to have some interior lights work but not come close to starting, I assumed it wasn't nearly enough time for the Alternator to bring back a completely flat battery.

I bought a Schumacher 8A Battery Charger and let it charge for 6 hours or so, took it off overnight and checked it just now and it read something like low 11s, which means it took some charge but is still way low.

I decided to check, then, for parasitic draw but I am not sure if my procedure is correct. I made sure everything was shut off, doors closed, ignition on off with key out. Took off the Negative battery cable and set my Multimeter to 10DCA and it read 00.62 - which equates to 620 milliamps. Obviously way too high but I've read that some Fords will read around 5-600 mA shortly after being shut off.

Thing is, I'm testing with the cable removed and the Multimeter is connecting the circuit between the battery Negative and chassis Ground, which would seem like it would draw high current on the initial connection - I'm essentially (I think) reconnecting the Negative cable.

Even if there's a parasitic draw of 600mA I can live with that as it'll be daily driven in the winter, I'm just trying to completely rule out buying a battery replacement since it was a $850 car. It did take a (partial) charge and is not that old. I'll try connecting the Schumacher again and letting it run for longer than remove it and check if I have Voltage improvement in the 12v range.

>>895752
Your battery is dead if you charged overnight and its only 11v.

Most chargers will take about 3-4 days to get to peak charge of nearly 14v, but if you left the battery completely drained for a month then its likely fucked. Especially if the battery is original to the car.

>>895752

Couple more things: Would have badly corroded chassis Grounds cause a draw condition? I'm planning on cleaning the main chassis ground connection, it looks pretty shit.

Also, when using the battery charger how likely is the battery to actually explode from the spark if I directly connect the clamps to the Terminals? I charged it initially using the clamps on the Terminals, but I'll run my jumper cable from the Battery Neg to the Charge Neg this time away from the battery. Thank you.

>>895754

It was only about 6 hours with a 8 Amp charger, and it's a 590 CCA Battery, so I'll try charging it longer but yeah, replacing it certainly isn't out of the question unfortunately. I did see a marked improvement though with those 6 hours. Thanks bro.

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This image is a miracle.

It's a 22 inch LCD monitor that I just replaced one of the two lamps in.

You never, ever replace one lamp. Ever. The colour temperature is always wrong, since they're never the same temperature/efficacy/brand/age/batch/etc..

I only replaced one because I didn't care. It's a test monitor. The replacement tube wasn't from an identical panel. It wasn't the same brand. Not the same age, not the same aspect ratio and not even the same size.

But it's a perfect match. There is no discernible colour difference between the old and the new tube.

This is impossible.

>>895765

I feel the need to check this rare occurrence

>>895757
probably a good idea to start learning what you can do to revive a lead acid battery.. pretty close to dead but you might be able to trick it for a while

>>895769

Yeah, I know Lithiums are pretty much dead once they drop below a certain voltage but assumed Lead-acid to be a bit more resilient. I took the battery out of the car to remove all drains and it appears to be charging normally now, without the 'bad battery' light.

So, all seems well for now I guess.

http://m.instructables.com/id/Simple-RGB-LED-MOOD-Colour-Potentiometer-Without-M/?ALLSTEPS

Can I do the same thing with 5mm rgb leds?

>>895991
I don't see why not. As far as I know RGB LEDs are usually a combination of Red Green and Blue LEDs with a common anode or cathode.

>>895992
yeah but i think the red color uses a lower voltage than the green and blue, so should the resistor for the red be different?

>>896009
No real need, since the currents are adjustable.

hey ohm, I need your help. where can I buy electronic components, I need some specific stuff but i really have no idea where I would start, Ive just been hoping i can find what i need on amazon or other pleb websites. thanks so much

>>896159

digikey

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I have a reciprocating saw I got for free because the rechargeable built in battery was shot. It says it takes a 6V charger.

My question is if I take 4x1.5v AA batteries and remove the rechargeable battery from the saw and connect the batteries to it will it work?

Pic related.

>>896186
Or if i take a 6V wall wart and wire it in?

>>896188
it likes current - a lot of it.

if you give it 6V it will 'work'. but that thing was probably awful to begin with.

>>896190
Opening it up it's just a battery, motor and a reciprocating bit attached to the motor. So I guess I just have to supply the motor with enough current?

The battery charges at 6v but is that what it discharges at? The motor only has this printed on it:

1060396
JOHNSON
3M3841

I could only find a 5V power supply, multimeter clocked it at 5.3v but it didn't turn, or sound like it wanted to turn over.

>>896194
The battery that was in it clocks 4V but doesn't hold a charge, this only just gets the motor going one revolution. I'm afraid I don't know the difference between current and voltage. Is current voltage x amperage?

>>896197
>>896194

look at OP's picture to understand current and voltage

>>896197
amperage is a word retards use for current
another retard word: ampacity

some people argue that saying 'voltage' is wrong
these people can be ignored

>>894325
you certainly can, just not directly

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>>896194
If its just a motor, simply get 2 18650's and connect them in series with the motor and it should work.

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in advance: I'm complete newbie in electronics, I'm chemical engineer and I'm currently building some gizmo for my work.

Quickie for you:

I have laboratory power supply that is connected straight to the LED array, no resistor or anything.
I use the power supply's build-in current and voltage limits. Would it be actually smart to have a fuse in the circuitry just in case something goes wrong?

That array is rated 3.6V and 9A, so putting a 10A fuse in there would be ok?
Does it matter that all fuses ive found are rated 12-24V or higher? (I have no idea what it means)

>>896331
It's not a bad idea, but you generally need very fast fuses if you're using the to protect semiconductors. Even then, it's more likely that you'll zap your LEDs with a reverse voltage spike, so I'd add overvoltage protection first.

The fuse's voltage rating must be higher than the highest possible supply voltage. If it's less, it's not guaranteed to operate correctly.

>>896338
i have no idea what overvoltage protection means.
I meant that fuse just in case some idiot (me) flips the wrong switch and suddenly turns the current limit off - its better to destroy fuse thats 50 cents that 350 euro LED array.

And about that voltage rating, so if my power supply is 30V max I can (/should) use fuse that is rated 120/240 V ?

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>>896343
oh, after some research let me rephrase my question:

Is there even a simple way to disconnect my LED array from power source in case that the current goes from 9A to 15A (give or take)?
Because it looks like fuses are suppose to protect from current that are multiple time highter than "normal" is that true?

>>896343
>if my power supply is 30V max I can (/should) use fuse that is rated 120/240 V ?

Yes you can. Fuses work fine at any voltage below their rated voltage.

Fuses blow because of an excess of current, which is something that is independent of voltage.

You can see this by looking at your power equations, conveniently laid out in >>891543: fuses actually blow because thermal energy is being put into them at a rate greater than it can leave, causing the filament to heat up and melt. Rate of thermal energy input (i.e. power) = R*I^2; R is the fixed resistance of the fuse, and I is the current passing through it. Thus power is not actually directly dependent on voltage, and an n-amp fuse will blow at n amps whatever the voltage.

The reason fuses have a voltage rating is because at a high enough voltage, anything conducts. Beyond the fuse's voltage rating, what can happen is that the fuse wire can blow, but that doesn't stop the electricity: it arcs between the two terminals, helped along by the conductive fusewire vapour. Inside the fuse's voltage rating, this doesn't happen and we're all good.

>>896349
thank you, that was very helpfull.
is there any chance you could answer my question in
>>896346 ?

>>896346
Fuse is typically just a piece of wire and you can't expect miracles from them. They're mainly used for short circuit protection, not for protecting against slight long term overloads. So, in this case you'd use the fastest fuse you can find to protect the LED against a failed power supply or some other similar fault.
Assuming you aren't running your LED at its absolute maximum current, the fuse has some chance at protecting it against long term overloads too, though.

Overvoltage protection can be handled by connecting a transient voltage suppressor (TVS) in parallel with the LED. Ones meant for 5V systems should be suitable. They're common, Google should help.

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>>896350
Hey man you can use fuses if you want but the problem with fuses is that they blow slowly if the current is just a little above their rating. They are hence used for protection against current much greater than their rating (like in the case of a short circuit).

Its much better to use a trip-switch (i'm not quite sure what they're called in english) which triggers a mechanical relay to turn off a switch if the current passing through it increases past a certain limit (like pic related).

They are usually made for AC, but it should work on DC too (i think) since current is independent.

>>896369
yeah, im not sure if there actually are any that would work at 3.6V and 10A

>>896378
Ok disregard what I said before. It seems the design used by AC circuit breakers would not work with DC current.

Breakers which run on 12vDC are available:

http://www.ebay.com/itm/ALTECH-E301611-ONE-POLE-480Y-277V-BREAKER-12vDC-10amp-Breaker-/221330354129

http://www.ebay.com/itm/SCHURTER-10-AMP-RESETABLE-CIRCUT-BREAKER-TS-710-250-125-VAC-24-12-VDC-/121798755639

But you're right 3.6 volts are hard to find.

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Alright, I have managed to solder the USB mini-b connector without fucking anything up.

Now, how do I compile the UsbAspLoader firmware in Atmel Studio? It's a WinAVR project, I have no idea how to import that.

Help.

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I have built this battery charger from a Velleman kit a few years ago.
The problem is that it has an automatic discharge function which always discharges the battery completely before starting the charge cycle. Is it possible to remove this feature, or at least make it selectable (on/off)? I plan to use it for charging a NiMh battery pack instead of NiCd so the discharging would not be necessary.

>>896442
See R34/R26?
Cut those lines connecting to A1 and A2. Should stop the auto discharge when you press start. Might make it more dangerous tho (attempting to discharge while charging probably won't be good).

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Just made this out of boredom

Why does browning paper with a lighter always sound like a good idea when it's a terrible idea

Where does resolution come in when generating a video signal?
Like in this picture, a waveform of a black and white composite signal, you get 53.3 us to draw a scanline. If you want to make a 320x240 image, how does that factor in? Do you just divide 53.3 us by 320 and designate that time to be the time of one pixel?

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>>896524
of course I forgot to attach the image

Question for the yuropeans here.

Where do you guys get your cheap electrical components from? I'm talking leds, resistors, capacitors, the basic shit. I'm from Belgium if that makes a difference.

>>896640

just take shit apart and throw the pcbs into a box

eventually you will have one of everything

Fuck /ohm/ I'm retarded

I tried to pry my 18650 cell from a cheap chinese holder, which apparently bonds with it and doesn't want to let it go, when I heard a quiet *pop*. I smelled it and was hit by an acrid smell, like acetone. Was I retarded enough to pop the pressure valve? FUCK

>>896486

...but why brown it? I don't undestand

>>896640

Ebay for assorted resistors, leds, pcbs, capacitors bought locally.

>>896660
Lol. They are sometimes soldered on those holders. Ya blew it senpai.

Is there a program I can use to find what kind of resistors I should use or should I just do the calculations by hand? I usually have guides but now I am trying projects without them and need to figure out what kind of resistors to get.

So those DC bench power supplies have a + - and gnd terminal right?

Let's say I have a simple DC circuit that's maybe a DC voltage source in series with a resistor and LED. I connect + to one side of the load but does the other go to - or ground?

For a more complex circuit like a differential pair amplifier or class AB push-pull amplifier would you wire + to one end of the load and - to the other since you need both positive and negative supply voltages? If so where do you connect ground?

>>896524
Yeah. You're free to use whatever horizontal resolution within reasonable limits. Allowed vertical resolution(s) depend on your monitor.

>>896640
Mouser, they ship for free if your order exceeds a certain dollar amount.

>>892719
Not officially recognized as DuPont connectors. DuPont is a company that did not invent that kind of connector, they invented Teflon, among other plastics. The .1" spaced square pin headers have been around since the 70's and they're used everywhere, but the push for more pins in a smaller space is beginning to encroach on their territory as dominant connector

>>892571
http://www.digikey.com/product-detail/en/0050579023/WM5298-ND/2731423

There's a starting point, company's Molex, big name in interconnects along with Samtech. From that page you can find the pins that go with it, and frankly you can take that connector I posted and just cut it up into smaller bits.

Stay smart.

>>894256
It's a trough design, so as long as you get the distance right, gauge right, whatever, sure. You should have plenty of those pins, so try one and see if it holds.

>>896695
Depends. If you have a single output power supply, the ground terminal is typically connected to the real ground (wall plug ground) and the +/- terminals are the actual floating output. In that case you'd connect the load between + and - and would optionally connect - to ground.
In dual output supplies without extra grounding terminal the ground (often marked 0 instead) is the middle point. You can connect your load between + and ground or + and -, but +/gnd (or gnd/-) is more convenient.

>>896524
>>896709
Technically, when using an analogue transport, there isn't even such a thing as horizontal resolution. It's analogue, after all. In principle, the horizontal resolution can be as high as you want, and in principle, a large and accurate enough CRT could display it.

In practice, you'll want to pick a normal, common resolution, because the first step a non-CRT takes is digitising your signal into a buffer so it can be blasted onto the screen. You'll get a better picture if you're outputting at a resolution that gets translated into a rational multiple of pixels, and if your pixel ratio is 1:1, you can address subpixels for nicer-looking lines.

>>896486
You shoulda stuck it in a clean, dry frying pan.

>>896486
Wanted to make it look like an ancient relic
I don't make my own choices, I just do what the autism tells me to
>>896742
Good idea

So I was on /g/ asking for help and someone re-directed me to here.

I'm trying to make a circuit that takes (2^n) - 1 inputs, tallies how many are true, and then outputs the number to n outputs (the number that are true in binary).

Originally, I was trying to do this making an Adder Tree but I realized that was wasn't going to work since I was trying to do 1 + 1 + 1 +...+ 1 like a tally, but the Adders interpret it as 111 + 11 + 11 +...+ 11 (in binary). So short of doing something like using a bunch of AND and OR gates to represent each of the (2^n)-1 numbers, which I really don't want to do since obviously this gets really stupid at large values of n, the implementation becomes something like at least ((2^n)-1)! gates, is there another way to get my result?

>>897257
You could do it with an adder tree, but you need to start from 1b adders and increase the width of addition by one bit at each level.
If there's no need for it to be a parallel implementation, you could just build a state machine which goes through all the inputs with a multiplexer and increments a counter for each true input.

>>897280
Sorry, I'm sure you can tell but I'm just beginning to learn some of this stuff so some of the stuff you're saying is kinda flying over my head. But for the inputs, this is on a breadboard essentially so they'll be turned on by individual switches and not a serial input or anything like that. I'm thinking >>897282 is the easier solution for me, although my circuit has to take simultaneous presses of keys so if you press two switches at the same time (I know its not possible but theoretically) it'll add 1+1 and increment the counter twice instead of just incrementing it once. I'm thinking thats what a state machine is for but I've never encountered one before.

>>897257
You need full-adders.

Say you've got three lines, connect it up; one adder.

Say you've got six lines, double the circuit, and you now have two two-bit values that you need to add. That takes a ripple-carry adder. Six lines, four adders.

Twelve lines, double /that/, stick another ripple-adder (3 bits this time) on the top of the tree. 11 adders.

24 lines, 22 adders, plus a four-bit ripple adder. 26 adders.

48, 52 adders, plus a five-bit adder. 57 adders.

n bits, 5n/3 + SUM( (1=>(n/3)), 5n) gates.

Assuming I've not gone done fucked up.

>>897290
Sorry, I might be misunderstanding adders but to my understanding, the inputs are arranged in binary such that inputs anbn are represented as 11 in binary (3 in decimal) whereas I want anbn to represent 1+1 for all n.

Proposed idea for my circuit, tell me if this it will work. I forgot what circuit this was but someone in the last thread mentioned I think it was a full or half adder where Carry represented 2 and output represented 1 so can I set it up so that ABC = 100 results in the output of the first adder outputs, ABC = 110, causing the first adder to turn off since the HA turns off the output but turns on the Carry, causing the second adder to turn on, and so on, such that each input represents 1 or 0, and adds the n inputs to make n outputs where the nth output (nth register output) represents the number n.

File: 12VPSU.jpg (41KB, 800x600px) Image search: [Google]

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Guys, I dont know shit about electronics so let me ask you this straight.

How does pic related works?
inb4 europlug
The sticker on it says:
Output voltage: 12V
Output current: 500mA.

Can I connect 12V pc fan straight to it and use it as power supply?
What if the fan is rated 12V/165mA ?

When the fan has lower current rating then the power supply is it save to use? Does it mean that it only "pulls" 165mA from the power supply? or does it mean that the power supply "pushes" 500mA into it and burns it?

>>897354
Yes, it is safe to use.

The current rating on the adapter is the maximum current it can provide. The current rating on the fan is the minimum current that it needs. As long as your supply current is more than your fan current, its perfectly ok to use.

>>897295
Yeah, they don't do that. Conveniently, though, a full adder does that for three bits.

Therefore, you need to build a tree, where:
n/3 full adders convert three items into n/3 two-bit values
n/3 full adders add these up into three-bit values
n/3-1 add these three-bit values into four-bit values
and so on.

i need to connect a microcontroller that runs on ~3V and a couple of PIR sensors that run on 5V

I have a 5V source, can I hook up a 3.3V regulator on it without decoupling capacitors? Do I need those capacitors if my 5V is definitely stable?

>>897401
One of the purposes of those capacitors is to stabilize the regulator. Dedicated input capacitor might not be needed if the regulator is reasonably close to the other 5V filter capacitors. Some regulators always need an output capacitor, some can do without.
But seriously, trying to jew on fucking capacitors...

>>897401
without the "inertia" of the caps, the regulator can oscillate or just not regulate properly.

I've seen it work without caps, I've seen it go crazy.
always add caps. preferably before and after the regulator.

making sure it always has a load isn't a bad idea either.

>>897416
yeah, never jew on the caps, that's for Chinese people.

>>897416
>>897417
how do i determine the capacity i need?

100uF on input and output too much or too low?

File: 6000v_neon_transformer.jpg (45KB, 643x340px) Image search: [Google]

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What safety precautions do i need to take around an NST and HV leads?

im a physcist, not an electrical engineer, so i know little about DIY. im building something that will run at 12-20kv or so for extended periods of time.

>>897433
The required output capacitor depends on regulator. See the datasheet. Assuming the input was already filtered, the input capacitor is typically just 100nF...1uF. Again, see the datasheet, they usually have suggestions for both capacitors.
100uF capacitors are typically something you use with switchers or with poorly regulated input.

>>897446
Don't touch it when it's powered on.
Prevent others from touching it.
Insulate everything well and if possible at all, put stuff to a grounded case.
Avoid bare wire and sharp edges as much as possible to avoid corona.
Use a proper mains fuse.
Use a suitable indicator to tell it's powered on.

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>>897446
>>897386
Why?

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>>897505
>thread had been up for 3 amd a quarter hours without any responses

Poor you.

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What happens when a reversed capacitor blows up?

I want to make this toy that is like Simon Says, but when you lose it blows a capacitor. Can I use a transistor to provide current to the reversed capacitor from the regulator circuit as the rest of the board, or should it be completely isolated from the rest of the circuit with something like a mini relay?

>>897361
I concur.

>>897550

Usually the vent pops (this is what they are designed to do) and magic smoke comes out (in an electrolytic cap)

If I were you, I would look into temperature tolerances of a given capacitor to make them blow easier by heating them. Consider finding a super capacitor with very low ESR, and building a circuit to charge it using a boost converter, then discharging through your exploding cap.

>>897550
once it blows up its fucked.
so it doesn't matter?

I have a PCB whose sections need the following operating voltages:
> 3.3V for logic
> +/-8V for opamps in audio filter
> +/-24V for amplifier
I only have a +12V supply and limited space so I can't just jam 4 supplies in there for the voltage I need. What would I use? The circuit will draw a total of roughly 8A. Also it would be nice if I could switch between symmetrical / asymmetrical supply (+/-24V vs. +48V)

>>897701
Here is a neat tool that allows you to determine the required PCB trace width for the required amount of current flow.

http://www.desmith.net/NMdS/Electronics/TraceWidth.html

As for the part about your power supply I would guess that you could use a single voltage source of the highest voltage you need and then use linear regulators to power everything else but there may be issues regarding noise (especially since you're using OP-amps and audio filters etc.) I'm not an expert on power supplies though, so maybe another anon can help you out there.

>>897702
Thanks for the tool.
> single voltage source of the highest voltage you need
Not possible. This is for an internship, I'm developing an audio filter / amp module that will be integrated into an existing system and powered off the system's existing PSU. And since they're cheap cunts and want to downsize the PSU to 12V because EMC, and space constraints mean they can't jam more PSUs in the case, I have to find some kind of step up converter that gives me my 24V, and an inverter to get -24V from that as well. Preferably both in one component.

>>897702
>>897706
Oh I'm using a step down regulator to get my 3.3V though so no problem there. I was going to get +-8V from the +-24V with a some simple high resistance voltage dividers. The problem is mainly how to get +/-24V from a +12V input

>>897707
Look into boost converters. You could probably use a simple h-bridge to invert the voltage.

http://www.ti.com/product/tps55340-ep
https://en.wikipedia.org/wiki/Boost_converter

>>897706
>want to downsize the PSU to 12V because EMC, and space constraints
You need switchers to produce +/-24V from 12V and unless they're well-made, you have a good chance of wasting the little size and EMC advantages the 12V PSU gave.
If it were my design, I'd check first if the amplifier really, really needs +/-24V. For example, is it possible to use a BTL amp or lower impedance speakers (or whatever the load is).

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>>897701

i dont have a specific part for you but these sort of things do exist. for example, this ''picoPSU-80, 80w output, 12v input DC-DC Power Supply'' takes 12V in and generates +3.3, +5, +12, -12V etc for powering a computer.

>>897715
I already tried reducing the operating voltage and I absolutely can't go lower than +-19V. Speaker impedance needs to be 4 Ohms or higher. The amp already uses a BTL configuration.

>>897721
In that case you can at least drop the requirement for a high power dual supply.
Also, if you really need >150W output power and you need a >150W switcher for providing the power for the amp, there's a good chance it makes sense to reconsider the main supply. Talk to your boss, again.

>>897730
Will do.
For now I found this, and I hope it'll be adequate for my needs:
http://cds.linear.com/docs/en/datasheet/3957afa.pdf
I'm not sure about the maximum current I'll need. The amp itself (which is what's drawing most of the current) allegedly outputs around 30W RMS, delivered into a 4 Ohm load. That means an RMS current of 2.74A, which means a peak current of just under 4A. If we only use 10W speakers (thus further reducing the maximum signal amplitude) I end up with around 2.23A. The MCU I'm using the 3.3V for might draw another 200mA, maybe 500, but that's pretty much it. So I _should_ be fine in that regard.

Still looking for an inverter to get -24V. Should I just set up another 3957 in parallel with the first to go +12V -> -24V (use feedback resistor to set output voltage to negative), or should I get an inverter that takes +24V from the 3957 and inverts them?

File: 12v to +-24v.png (7KB, 1012x326px) Image search: [Google]

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To illustrate the last paragraph:

>>897734

Just remembered, the whole shebang has 2 channels, so in the worst case (both channels draw current in phase, doubling the current drawn from the PSU) I'd end up with around 9A being drawn from the PSU. Obviously the 3957 can't handle that.
But if we limit the output to 10W (shitty speakers can't take more anyway) and only use one channel (both are used for independent audio signals), the current draw is low enough that one 3957 can handle it.

Talked to my mentor, here's what I'll do:

> external PSU gives 12V
> I use 2x LT3957
> one boosts 12V to +24V
> one inverts and boosts 12V to -24V
> plan alternative low-power variant that only uses one LT3957 giving me +40V, 5A max, and disables one of the channels

Now to figure out the resistors, caps, inductors and diodes the 3957 needs...

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>>897257
>>897295
>>897383
Okay, so I've been busy lately, but I feel like I have a circuit that's close to what I wanted now (the blank boxes are Half Adders). But this seems like a weird configuration of results since the outputs are 1, 2, 2, and 4, but I still don't know how to add the last input.

>>897734
A BTL amp running from a single 12V supply would be able to produce more than 10W to a 4R load. If 10W is enough, you could omit the boost/invert switchers altogether.
The switcher you mentioned has 5A *switch* current limit. It won't be able to produce 5A (or even 2.74A) when boosting 12V to 24V.

>>897736
Generally speaking, the rightmost method works better: you can use smaller positive switcher, the voltage stress is smaller on the negative switcher and the efficiency of the negative output isn't reduced by the efficiency of the positive switcher.

>>897792
No. Only the first stage tallies single bits. Their outputs are in 2b binary format, so you need adders with 2 x 2b inputs in the second stage. Then you need an adder with 2 x 3b inputs in the third stage.

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>>897827
I'll be honest, I don't know how to build a 2-bit or 3-bit Full Adder, so I drew this circuit diagram instead. Is this what you're talking about?

>>897835
Yes, and Google etc. tell you how to build n-bit adders.
https://en.wikipedia.org/wiki/Adder_(electronics)

>>897839
Thank you so much, my circuit is working, but just to make sure, an (n > 2) n-bit Full Adder is just a Ripple Carry Adder with n Full Adders?

>>897823
>A BTL amp running from a single 12V supply would be able to produce more than 10W to a 4R load.
If you're talking about normal class A/B amps, sure. This is a class D amp, meaning that the analogue signal is pulse-width modulated (actually delta sigma in this case), which yields a rectangular signal with varying duty cycle (duty cycle being proportional to the analogue amplitude at the input, but the output amplitude always being either high or low level), which is then amplified using some FETs, which is then low-pass filtered to obtain a continuous waveform again. This means that even if I'm putting an average of 10W into those 4 Ohm speakers over a long time, the PSU still has to deliver spikes of current that are as high as what I calculated (up to around 9A, worst case).
I already tried using the amp at lower supply voltages but it absolutely does not work at under +-19V no matter how small the output signal is over time.

I looked at the 3957 datasheet; the 24V boost circuit gives 600 mA but the current only really seems to be limited by the schottky diode at its output. I figure I'll replace that with one that lets more current through, and see if it blows up the converter. If yes, then I need to find another way (or convince my boss to give me 4 external 12V PSUs so I can get my +-24V)

>Generally speaking, the rightmost method works better
I figured, so I'm going to use that (assuming the thing doesn't blow up if I try to pull 7-8 A in short bursts)

>>896836
>Wanted to make it look like an ancient relic
I've heard of craft-y people doing this to paper ietms by putting it into a cookie pan in the oven, pouring in enough (brown) tea to soak it and then putting the oven on low heat until the pan is dry.

File: +8v.png (24KB, 647x313px) Image search: [Google]

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Power supply guy again.
Still going to be using 2x 3957 for the main supply (boosting +12v to +-24V).
I thought I'd redesign the part of the PSU that gives me my +-8V for the opamps and now that I'm done drawing the part that will give me the +8V I'm wondering how to use the 2675 to obtain -8V. According to the datasheet it can be used for a positive-to-negative converter, but nowhere does it say how I would go about this.

>removing led bulb flicker
I bought a led replacement bulb for one of my lamps but I can't stand the flicker. Is it just caused by the AC wave? Can you buy AC to DC converters and run a lamp through it?

>>897871
In it's simplest form, yes. A step further would be a carry look-ahead adder. And as a side note, what some people do is use a half adder as the first stage (no carry-in implied) and then ladder with full adders.

>>897874
Class AB, B or D, you can get >10W output from 12V supply. The filters on class D amp's output are there to remove the spikes (well, attenuate them) and whatever spikes you see in the power input side, you're supposed to kill with sufficient bypass capacitors. If properly done, your class D amp draws about the same amount of current as a basic class AB amp does. You don't need a special PSU to feed it.

Maybe I'm misunderstanding something. Like, you're forced to use some ill-fitting ready-made amplifier for whatever reason and since it won't work at 12V, you need a step-up switcher for it and there's no way around it.

>>897871
Ripple carry adder is the simplest way to implement an n-bit adder. There are several others as well.

i need to program a uc to perform a simple function as blinking a led when a sensor detects movement

the uc is MSP430, how do i even start with this?
is it possible to program it without the libraries supplied in their IDE?

>>898297
>Maybe I'm misunderstanding something. Like, you're forced to use some ill-fitting ready-made amplifier for whatever reason and since it won't work at 12V, you need a step-up switcher for it and there's no way around it.
Exactly. But hey, I stopped worrying about it for now. Told my boss I either need a different amplifier, or a PSU that can give me the current I need at the voltage I need. This is all an internship, so it doesn't even really matter if I finish the thing or not, especially if there's just no way to do it with the limitations they give me.

>>898323
can't help you with reading data from motion sensors, but i should mention that if you're using TI's disgusting bloated CCS IDE you might want to google "energia" and try that instead.

Is their any reason winding a solenoid around wood wouldn't work

>>896392
wow this is cool. what is it?

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Does anyone know of a good reason to get a 6.2ghz spectrum analyser? I've come across a good deal (still around $2k) for pic related but can't think of any use for it for myself.

>>892702
>>892703
r8d

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I have a giant X/Y oscilloscope monitor. What do?

>tfw I spent 8 hours total getting this stupid program to count how many times i clicked a goddamn switch
Fuck labview

>>891543
Spin it! I'm ready!

>>898717
Buying something just because it's a good deal is rarely a good idea.

> Buying something just because it's a good deal is rarely a good idea.

unless you can find a radio engineer and can sell it to them for a profit. no mere mortal is gonna spend $1000 for a musical light show.

What's a good "cheap" oscilloscope with two channels and at least 20MHz?

>>899005
Some decades old clunker will give you the most bang for the buck.

Hello /ohm/, I'm looking to make a 3-way audio splitter which will take 3 mono wireless microphones as inputs and will output to a female connector which will then be connected to a mixer. Is it as simple as connecting all signal wires to the output socker with 4.7k resistors in series with each input and joining grounds together? Will that work?

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>>899156

Added picture for clarity with an additional question. Can I use the output signal and connect it to both left and right channel in case they have a stereo audio system?

>>899156
>I'm looking to make a 3-way audio splitter

you're joining signals, so dont call it a splitter.

>will output to a female connector which will then be connected to a mixer

here, like all noobs, you're adding useless detail that just confuses the issue. who cares what sex the connector is? if you have a mixer, why not use the mixer to mix the 3 mics? not enough inputs?

>Is it as simple as connecting all signal wires to the output socker with 4.7k resistors in series

yes. however 4.7K seems too high, and will attenuate volume. a typical mic is 600 ohms, so you'd wanna use around 600 ohms. plus, after the 3 resistors, you probably wanna add a 5K to ground.

>Can I use the output signal and connect it to both left and right channel in case they have a stereo audio system?

yeah, no problem. it's possible the mixer will do that automatically for you: put the mic inputs on both L&R outputs, coz it would sound odd if the singer/speaker was only heard from one side.

>>899165

Mixer is unknown (we'll be playing for a contest, and we don't know what equipment they have. Better to be prepared, especially since a few connectors and resistors isn't a big investment).

Other than that, thank you very much!

>>899170
I don't recommend joining 3 mic signals together, especially if you're using the venue's mixer and sound guy, it'll drive him absolutely nuts, more-so in the case of wireless mics (I assume you're going to be moving around a bit with them). Can you phone the contest people and ask about the number of inputs the mixer can take?

What would be the consequence of hooking up a unipolar stepper motor incorrectly as a bipolar?

I got a couple of single-axis nema34 CNC drive kits of ebay some time ago... a motor & driver. Both of them work.
One is smaller (a 850-oz motor) and the other is larger (a 1600-oz motor). The smaller one is a unipolar (8-wire) and the larger is a bipolar (4-wire).

Even though both of them don't have much of a load and are spinning less than 10 RPMs, the smaller motor gets hot and vibrates a lot. The larger motor stays room-temperature and runs much smoother.

When I got them I looked on the motor manufacturer's site to find out the wiring, and I checked them with a voltmeter to make double-sure I was connecting them properly. I wired them with the coils in series; the driver's only got 4 connection points.

They don't really need more speed or torque; these motors are pretty huge for the load I'm using them for.

I can't get to my past orders on ebay ATM to get to the manufacturer's website (I don't recall it)...

>>899231
I am *almost* certain that this is the page for the motor:
hXXp://www.longs-motor.com/productinfo/detail_12_25_120.aspx

and I have the yellow & blue wires joined, and the brown & orange.... as shown toward the bottom-center of the page...? Should I try the right-side way?

The kit was sold by Long's and the motor wasn't this same model number, but this is the only 1.8-degree unipolar stepper they show on their site.

>>899179

It'll probably come down to me to take care of sound, since their sound guy couldn't even play soundbites he was supposed to on time. Also, how will this drive him mad, anyway? He still gets one output to connect to the mixer and my contraption is passive and maintenance-free after connecting the receivers.

On the other hand, we will be buying those mics soon, we don't have them yet. I'm wondering if cheapos we buy will broadcast on the same frequency, so only one receiver will suffice. We'll see.

>>899272
If you have 3 wireless mics, there would need to be 3 individual transmitters, and 3 individual receivers. You can't broadcast 2 mics over one frequency or they will be competing with each other for signal dominance. In short, you will get shit signal and lots of noise.

3 wireless mics means the FOH sound guy gets 3 mic inputs to use. Even if you decide to run your own sound for monitoring or whatever, you should still send those 3 individual signals to the FOH mixer. Not having control of individual mic levels won't make your sound guy happy, no matter how competent he is. He controls how you sound so don't piss him off. Wireless mics and lots of moving around requires constant vigilance. If you decide to do this, make sure you the 3 mics broadcast on 3 different frequencies.

Why do you need 3 wireless mics anyways?

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I need some help with setting up an audio system.
There are six 6.35mm jacks in the back of a Jansen P.A.80 (small NZ comany in the 70's), two are obviously for speakers because they are labelled such, two are near a label saying "monitor" and are hooked up to a switch ("P" and "S") then linked to the speakers when the switch is flicked to "P" (I have no idea what is going on here) and two are wired to the volume control. It's all mono.

Can someone explain what I can do with this stuff?

If I have sets of speakers and they are set in series within the 16 ohm max impedance for the PA, how do I work out how the watts rms will effect the speakers?

Related to the watts: Can I put a potentiometer as a simple volume control on each speaker so that I can adjust each speaker's volume depending on the position of the listener?

>>899272

dude, you didnt mention you were gonna use wireless mics. that changes some things. most important is that wireless receivers put out a line-level signal (around 0.1V) as opposed to milli-volts for wired mics. so you can use the line-level inputs on the mixer, of which there should be a lot. even a super-low-end mixer like the Alto ZMX52, gets you 1 mic input and 4 line inputs.

>>899354
>You can't broadcast 2 mics over one frequency or they will be competing with each other for signal dominance

in theory there's nothing wrong with that approach; the signals should just mix at the receiver. it's like two people talking on CB radio on the same channel: you hear them both.
they'd just have to co-ordinate their relative volumes by changing distance to mouth.
anyway, the dude can experiment with this by hooking a receiver up to his stereo. and returning the extra receivers if it works. good ones are kinda pricey.
i could do a test here with my own wireless mics, but it's kinda late to be making noise.

>>899363
>Can someone explain what I can do with this stuff?

throw it in the nearest trashcan. old equipment, like old people, is nothing but frustration. if you wanna make some noise, you can get a thrift store 100W+ stereo for about $10. or a new class D amplifier like this for $30:

http://www.amazon.com/Nobsound-Excellent-Quality-TDA7498-Amplifier/dp/B016IOUZFQ/ref=sr_1_7/187-9406058-3157834?ie=UTF8&qid=1446963260&sr=8-7&keywords=TDA7498+100W+%2B+100W+Class+D+Amplifier+Board

if you persist in your madness...
- "monitor" is usually a local speaker that monitors the remote main speaker.
- S and P may refer to serial and parallel, as in you can connect the monitor in series or in parallel with the main speaker.

> 16 ohm max impedance for the PA

you probably mean MIN impedance

>Can I put a potentiometer as a simple volume control on each speaker

yeah, big expensive 20W pots. better drop that idea.

>>899364
The reason why that isn't done in A/V and sound production is because you get a really shitty signal full of ugly noise and crap balance. Wireless receivers aren't mixers. I just don't think the setup is feasible for a concert/contest situation.

Plus, wireless sets are sold as such with one receiver for each transmitter. It'll be hard to return just a receiver.

Is it possible to rent some wireless sets for the day?

>Wireless receivers aren't mixers.

just a quibble: all radio receivers are mixers by nature. if you have ten radio stations broadcasting at 100Mhz, you will hear all ten simultaneously on your radio receiver, with volumes determined by received power levels.

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>>899366

Whoa. That is one cheap amp. But I like this one. The mono is annoying but as a base, it's pretty nice (microphone 3 makes a bad exceptionally high pitch scream its volume is turned up). Still, I am concerned that I don't understand the specs well enough to not explode something.

Thank you! The monitor makes perfect sense, the switch didn't seem to be wired to series or parallel when I was playing around with a multimeter but I'll check again.

I don't think the 16 ohm is minimum impedance, unless I'm reading this table incorrectly, and it wouldn't surprise me if I was reading it incorrectly.

>>899389

minimum impedance is 4 ohms, but 16 is not a maximum, coz there is no so such thing as a maximum speaker impedance. if you go higher than 16, you just get less power out. coz of ohm's law.

the first photo is too dark to make out the wiring, so you're on your own.

>(microphone 3 makes a bad exceptionally high pitch scream its volume is turned up)

every amp does that. it's called feedback.

>>899389

the fact that the 3 mystery jacks look to be isolated from the case by plastic washers strongly suggests they're inputs. for music or whatever.

>>899395
No max impedance? You just get less power out? ... I'm going to spend a few minutes thinking about this because it changes everything. But thank you, that is awesome.

>microphone 3 feedback
Nah, not like that. Some wires are crossed or corroded or something in the volume knob and if it's turned "on" to any value<0 then the amp produces the high pitched noise. If the volume on Mic 3 is turned down so low as to be 0, it is fine. I'm not really concerned about the mic inputs.

> isolated from the case by plastic washers
Sorry, both of those pics are of the same back panel. Def inputs, they are grounded together from the inside. The Gram/Tape input is on the front.

Quick question - I'm mounting a disc on a servo motor with its center axis parallel to the axis of rotation. I need a quick a dirty way to figure out how the weight on this disc (pressing down on the axis of rotation) will affect the torque. My guess is that it depends on the coefficient of friction of some internal gear, but I have no idea what sort of ballpark value to use. I'm using an all-metal gear mini servo rated for 1.5kgfcm at minimum voltage of 4.8v.

Apologies if this is not the right forum for this question.

Just thought I'd let you anons know that The Art of Electronics - Third Edition is finally available on libgen (and it doesn't seem fake to me).
Some of the links don't work, but the second one werked for me. The quality of the scan is bretty shit, but you can read it, and that's the only thing that matters.
And no, I'm not talking about the chapter 9 only version, it's the full book.

>>899569
What? The whole of chapter 1 is there. Are you sure you downloaded the right one? It should say 2015 in the year column.

>>899564

i'll wait for the movie.

>>899795
Come on mate, the movie is always worse than the book.

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Fellas pls help

So I'm researching switched mode power supplies (buck) and understand that you can quite easily control the output voltage by simply changing the duty cycle of the switch (say a MOSFET).
But how on earth do you adjust the maximum output current (at a set output voltage)? So far I can only see using a lossy current limiting component like a BJT to achieve this, or are we able to somehow do it with just a single MOSFET which would control both current and voltage.

I have tried rearranging Duty = Vout/Vin to be in terms of current, Duty = Iin/Iout (efficiency taken out). So I guess you can change output current by simply changing the duty of the switch, but doesn't that also mean you would be changing the output voltage as well? I feel like I’m just going around in circles…

>>900098
>change voltage changes current
uh, thats exactly how electricity works ya goof!

>>900098
Ohm's law it.

>>900103
>>900101
But here is the thing, I want to be able to keep my output voltage constant and have an the output current adjustable. A super easy method is just to stick a BJT on the output of the buck converter and vary the bias current on the base, but I was wondering if you could somehow use the buck's MOSFET for it. Guess V=IR says no

>>900127
>keep my output voltage constant and have an the output current adjustable
AAAAAAAAAAA
WHAT THE FUCK IS WRONG WITH YOUR BRAIN
that's literally impossible unless you're controlling the goddamn LOAD

>>900127
if you have some component that that can magically calculate and draw the available current while drawing a constant voltage then that will happen.

you cant set V and I, you set one (usually V) and the other depends on the properties of the circuit.

consider your transistor idea, draw it out with a load resistor or something and then work out what the voltage drop is across the output as the current changes.
pro-tip: voltage will change too

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>>900128
U fooken wot m8

You can easily limit the output current with a BJT (limit it up to the maximum output current of the buck converter that is) using a constant load. Just look up simple current limiting circuits for high power LED's (http://www.pcbheaven.com/userpages/LED_driving_and_controlling_methods/?topic=worklog&p=1)

>>900130
psssst
hey anon
guess how it adjusts the current?
CE resistance changes and therefore the CE voltage drop changes and therefore the voltage across the LED changes.
back to school with you!

>>900133
OK m8,

Lets use a TIP31C BJT to control the output current. Say I have a 12V @ 1A going into my magical 100% efficient buck converter giving me a total input power of 12W. Now I want the output voltage at the load to be 5V (giving me a max current of 2.4A, 12/5), but I want to limit this current to 1A.

So I use my magical BJT and connect that to the output, now at Ic = 1A the BJT has a Vce(sat) voltage of approximately 0.2V (and you are right the voltage does change with current, so with 0.5A it’s 0.1V, and with 0.1A it’s 0.05V). This means that the output voltage of the load would be 4.8V (5-0.2), not hugely different from 5V but different enough to perhaps warrant some sort of feedback into the buck converter saying up the output voltage to 5.2V so that my actual load sees 5V after the BJT.

If my calculations/assumptions are wrong then please tell me so I can master the art of magic tricks.

>>900135
Current limiting is different than controlling output current.

>>900141
My bad then, sorry if I confused people

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Hey guys, Ive just bought this LED aray and conneted it to my power supply. The PSU is running in constant current/voltage mode. Ive set my voltage to 3.6V and according to graph ive got from datasheet, the LED should be running around 8 amps. But it is not, anyone have any idea why?
Can it be because of unsufficient cooling? Resistance?

>>900575
Your wires look flimsy and that graph isn't meant to be 100% accurate in any case.

>>900580
yeah, those wires were the first around, I know I need thicker (its currently being made).

What if I crank up my voltage? There will be much more heat produced right? I was kinda expecting 25W (3.6*9 = 32) of heat. But if I have to raise the voltage.......

>>900581
Measure the actual voltage at the diode with a multimeter, You will then see the voltage drop of the wire/connectors.

Also, do you expect to get 8A from the power supply? Read the front panel.

>>900597
no worries comrade, if you look under the power supply that is turned on there is another one. That one is 30V/30A.

>>900581
Yeah, you crank up voltage. You should run your PSU in constant current mode to begin with and when you do so, you set the voltage higher than the highest expected load voltage.
The additional power dissipation in LED doesn't matter that much (it's designed to run at whatever voltage is required to push the nominal current through it) and your thermal design doesn't look like you spent much time on optimizing it.
Btw, the volt meter of your PSU isn't necessarily that accurate, either.

>>900575

it's entirely possible they sold you an underpowered LED, a 15W instead of a 30W. fakes are quite common in chinese-sourced units. if i were testing it, i'd make sure the current is limited to 5A (by shorting the output), and just crank up the voltage as high as needed. the LED will either give you close to the rated power if it's real, or burn up if it's a fake.

What is the reverse breakdown voltage for a LED? Can I use two in antiparallel and in parallel with a motor to indicate the direction it's going, if I make an H-bridge out of a DPDT relay?

thread about to 404?

>>900723
Depends on type, but 5V is a common value. Check the datasheet, if you're interested.
And yes, you can connect two normal LEDs in antiparallel. Some bi-color LEDs are actually connected internally that way.

>>900724
If you're going to start a new one, put the pastebin link to OP, >>892275

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new thread

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