#128 ATtiny TotalSleep

Test a total power shutdown with an ATtiny85 processor on a breadboard.

Here’s a quick video of the circuit in action:

Notes

The ATtiny SleepMode project showed me that even in CPU sleep mode, an ATtiny85 circuit can still draw something in the order of 238µA.

This project tests a scheme for total power shutdown triggered by the microcontroller itself. The circuit then draws virtually no current (certainly less than 10µA - the resolution of the ammeter I was using in-circuit).

The trade-off is that the circuit requires an external trigger to wake-up again. Here it uses a push-button.

How it works:

• power is supplied to the ATtiny and other circuit elements through a p-channel MOSFET (I’m using a BS250 here)
• when power is turned on, the 1MΩ resistor charges the 100nF capacitor with a time constant of 100ms
• this keeps the FET Vgs negative long enough for the ATtiny to power up and apply a high signal to the base of the NPN transistor
• the NPN collector-emitter conduction holds the FET Vgs negative, and therefore “powered on”
• when the ATtiny wants to power-down, it brings the NPN base low, cutting the collector-emitter channel, and sending the FET Vgs to 0V.
• this turns off the FET and everything is powered down. The current drawn in this state is limited to leakage of the components
• to powerup, the push-button shorts the capacitor, bringing the FET Vgs down and setting the cycle off again

This all seems to work very reliably.

Construction

Credits and References

• ATtiny85 datasheet
• BS250 datasheet
• BC547 datasheet
• Arduino DigitalPins reference
• Topic: Circuit for MCU to control its own power on/off - another approach using a flip-flop
• Self Shutting Down Arduino - describes a similar approach, but one that may not work depending on the specific p-channel FET used (I could not make it work with the BS250).