Power saving on station shutdown

[bergie]

As discussed separately with @berlincount and @kristall, we should implement a way to centrally manage power usage of all non-essential parts of the c-base IoT network:

• Shut devices down (or enter power-saving mode) at station shutdown
• Start up again when station opens (could be automatic, could be manual)

Optimally this would happen via a specific "shutdown" message on MQTT, triggered from the c-leuse shield switch, but pending that we could add a separate NodeMCU-powered button next to the shield console for sending this message.

So far the communication has been that there is no desire to broadcast a "station open" state outside of c-base, but we could still provide it on the crew network for IoT devices to start up. Assuming the sensors are running, there are of course some proxies for this information like door open/closed state, lights, motion.

Info screens

Two options to consider:

• Shut down the Raspberry Pi cleanly (but then the problem is starting it up again, since RPis don't support Wake-on-LAN)
• Keep RPi on, but disable HDMI

Either way, the screens themselves are the bigger power user than the RPi, and stopping the HDMI link should make them go to power-saving mode.

Sensor modules

The NodeMCUs consume 35mA on average on running (source). Since the sensor data is useful also for times when station is shut down, I'd recommend just keeping them running.

If this usage is a problem, we can make them go to deep sleep for some intervals when in shutdown mode and do WiFi connection and sensor reads only infrequently.

Other artefacts

The shutdown message could also be useful for some other artefacts, like:

• Siri: turn off display like other info screens, maybe turn off the lights?
• Ingress Table: turn off the lights
• Mate Light: turn off the lights

etc.

cc/ @uwekamper @ij0n