I just wanted to give you a heads up about Pi HomeGuard, I feel this is an excellent self build project for learning.
The idea was first featured on the Pi Blog and my Indiegogo campaign has recently been mentioned on the MagPi
The project currently has sensor solutions for:
Power usage, Temperature, PiR motion detection, Door Open/Close, Toilet Flush, Flood, Ext Temperature & Humidity, Rain Gauge and Wind speed.
The wireless sensors are self build but because the complexity is handled in the firmware they only need several components with minor soldering to complete. I feel the learning potential here is vast and once complete students will have a useful low cost system to monitor their family or property.
Each of the sensors has had its own challenges, an example is the Door sensor. To ensure detection, the open door event has to be held ON for several transmit cycles. On my first version I used a 555 timer delay circuit to hold the signal ON for at least 30 seconds. This added cost, complexity and the 555 circuit was not easy to build. This is now all handled in the firmware and we now only need two components, the sensor transmitter board and a magnetic door switch !
It would be great if my Indiegogo campaign was successful, let me know if you need any more details.
See Live demo at: http://pihomeguard.com