VM's Power Latching Circuit

Simple circuit that waits for external signal (button press, sensor going ->HIGH or -> LOW) and then provides power for microcontroller. After boot up the MCU uses output signal to keep the power on. After data processing, the MCU can shut off its power, therefore saving energy.

Ideall for:

• smart buttons
• security devices (PIR sensors, door/window sensors)
• battery powered devices

Inspiration

• Inspired by Embrace racing: https://www.youtube.com/watch?v=7D9L9oS4AJM
• Trigger high inspired by: https://randomnerdtutorials.com/latching-power-switch-circuit-auto-power-off-circuit-esp32-esp8266-arduino/

Princip of functions

Power up the circuit with Vin+GND pins. Power up the microcontroller with Vout + GND and connect the LATCH pin to one of the MCU's GPIO pins.

Choose the triggering mechanism (button, sensor, switch on board), use Sensor pins for connection.

When you apply power to the circuit, the MCU is powered off and the whole circuit consumes almost nothing.

After triggering (button press, sensor signal, ...) the power is routed to the microcontroller. The first thing the MCU must do after boot up, is setting the LATCH pin as INPUT_PULLUP. The MCU will be powered on as long as this pin is pulling HIGH.

When the MCU finishes with its job, change the LATCH pin as OUTPUT and set is as LOW. This will shut off the power for the MCU.

Maximum ratings

• Input voltage: 30V
• Input current: 3A

Configuration

Trigger by signal -> LOW

Don't need to solder Q2, R4, R5. You can either solder button SW1 and use it for triggering or route the triggering signal through the TrgL pin.

Trigger by signal -> HIGH

You need to solder Q2, R4, R5 and signal is routed through the TrgH pin.