Started 21st October 2016
Having given up on the idea of buying a cheap camera and using a micro-controller to make it do timelapse (see Timelapse) I saw the Adafruit Raspberry Pi Wearable Time Lapse Camera - Pi gives us a powerful enough processor and a camera with documentation.
The idea is to use an Arduino Pro mini as a real time clock (see Arduino 32768) and to control when the Pi takes photos. Power consumption by the Pi is huge so it will be kept powered down except when taking photos.
Power will come from a Lithium battery, charged by a solar panel. There will be a boost converter to produce the 5V needed by the Pi and another one to charge the battery from the solar panel.
The Pi and the Arduino talk via the I2C bus. Every so often the Arduino turns on power to the 5V boost converter, the Pi wakes up, reads the current time from the Arduino, takes a photo and then shuts down.
Photos of the boost converter obtained from ebay. This uses the GMT 5177 Synchronous Rectifier Step Up Converter. It has a pin to shut it down and uses less than 1 μA in this mode. To make this work it is necessary to break two tracks, reconnect one pin (bare wire) to the junction of the resistor and capacitor, finally the blue wire can be used to wake up or shutdown the converter.
Connecting the Pi camera cable the right way around