So I am using an UNO connected to an ACS712 current sensor to monitor an A/C electric motor. I want to monitor the electric motor's run time. When the electric motor hasn't run in the past 10 minutes, I'll put the UNO to sleep. This part of the project I have figured out, what I don't have figured out is how to wake the UNO up the next time the electric motor runs.
The ACS712 outputs a variable voltage depending upon the current it senses. It's about 2.5 volts wen there is no current, the motor is off. The voltage will increase when the motor switches on. The ACS712 is the 20 amp version and the electric motor is 110v 15 amp motor, so when the motor kicks on, there will be a change in the output of the ACS712. My thinking was to just use a transistor switch to trigger the wake up interrupt pin. Would this work?
If the input to the ACS712 is AC, so is it's output. So if the output voltage is at 60Hz, and that flips my transistor switch at 60Hz, can that be used to wake up an UNO?
I guess what I am really asking is, would one pulse on the wake up interrupt pin at 60Hz be long enough to wake an UNO up?
By definition, an interrupt trips on a level, not a duration.
A comparator is what, you would use.
Why are you putting a UNO to sleep? This is only relevant when using battery power, and a UNO is unsuitable for battery power as even in sleep mode, the USB interface draws power.
Since you are operating on mains power, there is no point introducing a more complex circuit simply to wake from sleep.
I understand this, but there has to be some sort of a minimum timing interval for this, correct? I mean, thinking this thru, if the interrupt pin is pulsed for 1/60th a second, the processor should pick up on that. I would hope... What would happen if the interrupt pin was triggered by a 2kHz signal, would the atmega328 register that as an interrupt? I guess I would have to look at the hardware docs for that info..
I mentioned an UNO to keep things simple and easy. I would actually be using an atmega328 and programming it via an USB to UART device.
As to why I would want to put it to sleep? My thoughts were "go green and save the planet" line of thinking.... But
You are right, why make the circuit more complex? At the end of the day, this thing will use less power than the speakers on my desk that I never turn off......
So a Pro Mini is a good choice for this as you have all the necessary support components (and an entirely unnecessary regulator and pilot LED "to boot") for much the same price as the MCU.
If you choose to make a PCB, you just mount the Pro Mini as a "daughterboard".
