How can I sleep a raspberry pi and wake it again with an interrupt?

To sleep and wake a Raspberry Pi using an interrupt, you would typically be looking into implementing a system where the Pi enters a low-power state and then is woken up by an external signal. However, it's important to note that Raspberry Pi models do not have a traditional "sleep" mode like laptops or PCs. The closest feature would be to halt the CPU or turn off various components to reduce power consumption, but this isn't the same as the sleep mode found in other types of computers.

For a Raspberry Pi, you can achieve a similar effect through software by shutting down non-essential processes or by controlling the power to external devices to save energy. Waking the Pi from a halted state can be done using GPIO pins, where an external signal (like a button press or a signal from another device) resets the Pi, causing it to boot up again.

Here's a basic approach to simulate sleep and wake functionality:

To Simulate Sleep:

1. Reduce Power Consumption: You can turn off HDMI, LED lights, or other peripherals to save power. For example, to turn off the HDMI output, you can use:

   /usr/bin/tvservice -o
   

   And to turn it back on:

   /usr/bin/tvservice -p
   

2. Software Shutdown: If you want the Pi to enter a state where it consumes minimal power, you might consider halting the system without cutting the power. Use the command:

   sudo halt
   

   or

   sudo poweroff
   

   Note that in this state, the Raspberry Pi is essentially off, and normal GPIO inputs won't wake it up.

To Wake Up:

To wake the Raspberry Pi from a halted state with an external interrupt, you would need to use a hardware approach because the software is not running when the Pi is halted.

1. Using GPIO Pins to Trigger a Reset: You can connect a push button or another signal to a GPIO pin that triggers the RUN pin to reset. This method requires physical access to the Raspberry Pi's pins.

2. External Wake-Up Circuit: You can build an external circuit that monitors a GPIO pin and then triggers the RUN pin on the Raspberry Pi. When the GPIO pin detects a high signal (from another device or sensor), the external circuit sends a signal to the RUN pin, resetting the Raspberry Pi and causing it to boot up.

   • You'll need to connect your external signal (e.g., a button or sensor output) to a GPIO pin set as an input on the external circuit.
   • The external circuit should monitor this input and then connect to the RUN pin on the Raspberry Pi. When the input goes high, the circuit momentarily connects the RUN pin to ground, resetting the Pi.

This setup requires careful consideration of electrical characteristics to avoid damaging the Raspberry Pi. It's also a good idea to have a debounce circuit or software to ensure that the Pi doesn't receive multiple reset signals in quick succession.

Remember, these solutions are more about reducing power consumption and rebooting the Pi rather than true sleep/wake functionality as seen in laptops and PCs. If your project requires waking the Pi based on specific events, you might need to keep it running at a minimal state and use software to monitor GPIO pins or other inputs for the conditions that would trigger a "wake-up" action.