A thunderstorm induced a blackout last night and 5 of my biggest

>>1219983
>detect if a 240vac device is working.

To detect presence of 240 vac is easy with a relay that pulls a pin low when power is present. But to detect proper operation something like your pressure sensor or an air flow sensor would be better. You could make a homemade switch that dangles in the air flow and is blown shut when air flow is present.

>>1219990
>is blown shut when air flow is present.

On second thought it would be easier and more reliable to use gravity to close the contacts and have the air flow open them. Just some sort of lightweight flapper that doesn't restrict the flow very much.

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>>1219990
>>1219992
Dafuq you talking about? Just use an optoisolator, you don't even need an arduino.
Use a bridge rectifier and a capacitor to smooth the AC signal to avoid rattling.

>>1219983
>runs on 12vdc
I like you.
You could use a relay to detect the pump failing because of an electrical outage.
Coil in parallel with pump, between the positive of the backup supply and the backup pump put in the switch side of the relay, one to common one to NC, normally closed.
While there is power to the pump the relay is held closed and backup is disconnected, during a power outage the relay is open and power flows to the backup pump from the backup battery.

This is about the simplest fail safe you can do and is very limited, it will not detect any issues with the pump branch circuit, the pump, the air lines etc, only the power feed and any wiring shared between the relay and pump.

Setting up monitoring of the oxygen in the tank with a computer or microcontroller is perfectly possible but I don't know that anyone here will take you through it step by step, best you will get is someone point you to a project, something similar or a suitable sensor that could work.

Good luck and sorry about your fish, may God have mercy on their soles.

>>1219998
>optoisolator driving a relay
Ever hear of the phrase 'hat on a hat'?

>>1219983
Arduino is making this unecessarily complicated. Like other anons have said just hardwire a normally closed held open switch to a relay or alarm. You only need to bring micro controllers into this if you want it to send you an email or something.

>>1220002
Wouldnt the relay switch on and off with 60hz because of the AC current?

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>>1220011

use an AC relay.

>>1220019
Generally better practice to switch power, not ground. The relay should be where the red dot is so that ground is always connected. In this case negative is floating, so not as important, but still.

>>1220019
>>1220022
Thank you kindly!

>>1220022

You're assuming OP is using negative ground. He could very well be using positive ground, e.g. the red dot.

>>1220024
>negative ground
>positive ground
Ask me how I know you are American.
Clue: It's because you are a fucking retarded idiot mongoloid that doesn't know the meaning of 'ground'
Now tell me something about 'amperage' please

>>1220019
this is the only solution

>>1220003
Optoisolators are rated for 100mA max, also transistors might not be the best for driving loads prone to huge inductive spikes like motors.

>>1220022
not important in DC

>>1220026
chill out

>>1219983
You could just use a computer UPS. Depending on the wattage of the main pump, the batteries could last awhile.

>>1220009
I agree, will need at least a Raspberry Pi for this.

>>1219983
Use a flow detector. A soon as the flow stops working the detector switches to whatever backup or alarm you have setup.

>>1219983
What about a bog standard computer UPS? Those can be had for fairly cheap.
Extra bonus.. find an emergency exit light. They are normally 12V, have a battery and charger. Plus they switch on when the power goes out.

>>1219983
I think the bigger concerns is why is your tank so poorly oxygenated that the fish died after 6 hours?

Clean your fucking tank and put some better plants in it. your fucking carp should be able to last for weeks.

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>>1220026
Boy I never get tired of posting this.

>>1220231
UPS will power 120/230v (delete as applicable), can just leave perm connected to normal airpump, lot also with an alarm trigger relay or whatever by loss of mains. Basically, score one cheap in ebay. replace battery (guaranteed fkd if 2nd hand), connect to system, forget about it. Obviously just run whats (emergency) needed through it, airpump etc. cant have that big a draw, should be enough juice to see it through most/every powercut. OR you could simply run a perm car battery charger, car battery and relay to 12v airpump as backup. But the last fucking thing you want in emergency setups where lives depend upon it, even overpriced fishlives, are Arduinos and shit. Dont crap the carp, man.

>>1220026
Feeling better now?
>something about 'amperage'
amperage is wattage over voltage and amperage squared is wattage over ohmage