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74HC595 Shift Registers

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Thread replies: 11
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reg.jpg
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I've just been learning how to use these. I have one IC and I've powered a string of LEDs with an Arduino, then moved onto driving a 1 digit 7 segment LED display and then a 4 digit version with multiplexing.

Now I want to elaborate with multiple LED matrices to make a large (at least 24 by 24) matrix (out of 8 by 8 ones most likely).

What are my limits with a single Arduino and its 5V supply, if I start daisychaining shift registers to drive such large displays?

At what point would I draw too much current?
>>
>>901539
with a shift register like that you can put all the leds on at the same time.
usually with more leds you make them into a squareish matrix, have a string of shift registers on the x and a separate set on the y.
turn on the leds one row or column at a time

then you calculate the power drawn from a single row or column because thats the maximum draw at one time

max draw from arduino is probably like 1A or something have a look at the regulator see what its rated at.
>>
>>901550
>regulator
Is that the transistor looking thing next to the DC in, or one of those round tin can things?
>>
>>901552
>Is that the transistor looking thing
probably its a to220 package if thats what you mean yes. check datasheet.

you can use a separate power supply as long as you connect the 0v's together.
>>
>>901552
>>901557
What actually are those two round aluminium things?
>>
>>902233
Surface-mount electrolytic capacitors.
>>
>>901539
>What are my limits with a single Arduino and its 5V supply
if you are using usb, then its whatever your usb allows, since the straight 5v for usb isnt regulated.
current limitations on usb varies.

if you are using the dc jack, then its whatever the regulator can deal with.

best is to use another regulated 5 volt source, like a phone/micro usb charger(usually 1 amp) or something.
connect this 5volt straight into the arduinos 5v. not the dc jack or the "5vin" pin, these go to the regulator.

lets do some quick back of the envelope calculations here.

lets say you run your leds hot @10mA.
24x24 matix? i guess we can assume that no more than one row will be lit at any one time.
0,010A x 24 = 0,24A

240mA isn't much. the usb should hande it.
the regulators too, so if the input voltage isn't too high.
>>
>>903483
Thanks.
>>
>>903728
no prob

quick correction
>>903483
>since the straight 5v for usb isnt regulated.
of course its regulated, just not by the arduino's regulator.

i just want to clarify in case you don't know:
regulators need a bit more voltage than what they regulate to(forward voltage drop).
so if you have 5 volts you need to connect it directly.

hence usb 5v not going to the regulator, but directly to the 5v rail on the arduino.
>>
>>901550
The word is multiplexing if you want to look it up, there is also charlieplexing if you want to have fun with tri-state logic. Other anons have properly explained the power issue.
>>
>>903890
tri-state on shift registers must be a pain, and duty cycle sucks when charlieplexing.
charlieplexing is for when you desperately need to squeeze out a few more i/o.
when using shift registers he can just add more in series anyway.
Thread posts: 11
Thread images: 1


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