How to make a circuit that can power itself off

Question

I am designing a battery powered microcontroller circuit that will spend the vast majority of its life turned off. (In the absence of other recommendations, I'm thinking a few AA batteries in series followed by a linear voltage regulator is what I'm likely to use, but if there are other solutions that are better suited to this application, I'm all ears.)

A physical toggle switch will be used to turn the circuit on. As long as the switch is on, the circuit will 'do stuff.' The physical switch is a non-negotiable part of the design.

When the switch is turned off, the circuit will need another 2-3 seconds to finish its work, then should be powered off. It can then remain powered off for months at a time. I would like to maximize battery life by reducing/eliminating current draw when the circuit is inactive.

What kind of power solution can I use to meet these goals? I imagine that I'll use a GPIO on the microcontroller to signal, 'hey, I still need power,' and will need some kind of 'logical-OR' power control that will power the microcontroller when either the switch or the GPIO pin is active.

Answer 1

^{simulate this circuit – Schematic created using CircuitLab}

When the switch is in OFF position and PMS not conducting, the 100k resistor keeps the PMOS in non-conducting mode.

When the switch is ON position the MCU starts and it drives GPIO ON High, pulls the 100k resistor low and brings the PMOS into a conducting mode, so that the PMOS bypasses the switch. When the switch is turned off the GPIO detect signal goes low, so you can then power the PMOSFET off and the system as well

Answer 2

This came up recently: How can I make this "automatic turn off" work using some GPIO pins on a MCU?

This circuit has the additional feature that it latches on, so that switch bounce won’t be a problem at turn-on before the MCU has had a chance to configure the GPIO. It can also use any kind of switch without regard to the current draw, so a membrane or carbon puck type can work. Finally, it could be modified to control an EN pin for a regulator instead of a FET.

Try it here