Problem with restarting solar-powered Pi Pico

Thread Starter


Joined May 16, 2024
I have built a Meshtastic node using a solar-powered Pi Pico. This works fine when the sun shines, but if the battery runs flat overnight then it does not restart cleanly when the sun returns - because the startup current drags the battery down.

What I need is a switch between the battery and the pico that turns on when the supply reaches 3.9V, and turns off if it drops below (say) 3.5V.

I know there are very cheap dedicated chips that can do this, but I can't find a supplier of small volume at reasonable postage costs! So instead I would like to build a circuit with discrete components. I'm pretty sure that I need a zener diode, an FET, and a resistor or two... but I can't get my head around what the complete circuit would look like.

Any help or pointers greatly appreciated! Thanks.