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The completed switch and timer relay. The red and black wires are the 12 volt supply, the pink is the 12v out to start the heater and the twin core cable with the block connector on the end is for the light dependant resistor. The LDR detects the mobile phone screen lighting up and triggers the unit.
The timer itself is a SPDT 10 function timer,1sec-100hr. RS part number 385 6957
The light sensitive switch is a modified version of this unit from Maplin http://www.maplin.co.uk/Module.aspx?ModuleNo=28574&criteria=light%20switch&doy=20m9
The timer is set for 30 minutes but it is straight forward to adjust.
