EEVblog Electronics Community Forum
Electronics => Beginners => Topic started by: mortrek on July 27, 2019, 09:04:29 pm
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I wanted to create a 'low battery' indicator for an ATmega328p in a very low-current setup that runs from alkalines and spends most of its time in sleep mode. I was thinking that during some wake cycles, it could check an ADC connected to the battery source (hopefully it's really low leakage...), and if it's below a certain threshold, switch some indicator on that takes basically 0 power to maintain. Something like a latching relay, but an indicator. It could be a small white/red dot, or something similar, I don't care. Something very simple, and takes like 1 digital output to switch it on from an ATMega, preferably directly from the pin (so, very low current). I'd prefer to switch it off manually with a button or something. I don't care if it's 1mm in diameter, it just needs to be visible. It needs to stay indicating when power is removed.
To be clear, I just want a the lowest-current low-battery indicator possible, to indicate the capacity without draining the batteries unnecessarily. If something discrete from the MCU would work for that purpose, I'm fine with it. The battery setup is 3 alkalines in series, so ~4.5V nominal to about ~3V cutoff, but I want the indicator to 'indicate' closer to 3.3-3.6V.
Is there a name for this type of thing that I should be searching for? I'm trying different permutations of keywords and just getting a lot of other stuff.
edit:
Ok I've found flip dots... I forgot those existed. I'll look into those further.
edit2: Do they make flip dots / flip discs that use <40mA and activate with <=3V?
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This project is using small pager motors to create DIY flip dots which can be powered with < 3V:
https://hackaday.io/project/18541-dot-flippers/log/62647-progress-in-diy-flip-dots