Although the power drawn by the RaspberryPi is very low for a computer, its still significant for battery powered equipment such as my bird box monitor.
So here is an idea to reduce power consumption during periods of inactivity.
During the early weeks of the nesting season, visits by birds to garden nest boxes may be infrequent. Typically here in southern England, garden birds may start checking out nest sites during February, with more activity running into April, when nest building typically gets under way.
So although there may be plenty of activity to film during May and June, for the early months it would be nice to have a way to save power by automatically powering on/off my RaspberryPi BirdBox system.
As my box will include an activity sensor mounted within the entrance hole to the box, the idea is to use this to trigger the power-on sequence.
Once the RaspberryPi has booted, an application will run and use the monostable as a watchdog. Basically this means that as long as the dog is kicked from time-to-time, the Raspberry Pi will remain powered up.
But if my program determines that there has not been any activity for longer than a certain period, the dog is allowed to sleep and the RaspberryPi is powered down.
Naturally if my program crashes or hangs (or something else really bad happens) the watchdog will also shut the RaspberryPi down. Subsequent activity will restart it.
Clearly this is not a rapid response system. Delays in powering up and powering down relate to the boot time and shutdown response of the RaspberryPi. But this approach should be fine for this bird box application.
The addition of a light sensor may be a possible refinement. So during the hours of darkness the system, and the birds, are allowed to sleep!
During the next few weeks I hope to find the time to prototype this using (what else?) a 555 timer chip. I'll then be able to post a proper circuit.
BirdBoxPiCam 2014: #1 The Plan
RaspberryPi: keeping time without the internet