With the aid of a breadboard, wires and crocodile clips, I have set up a basic circuit consisting of a 9-volt battery, a rheostat and a motor. The circuit works, but when I add a supposedly light-sensitive diode to it, the motor runs whether the diode is covered up or not. This is the case both with a conventional photodiode and one which is specifically supposed to work only in visible light.
I thought this was a fairly straightforward circuit, as I remember such arrangements being put together at my secondary school for parents' evenings. However, I'm obviously missing something somewhere.
In order to get a motor running, powered by a PP3 battery, only when the room is in daylight (so if, say, the circuit were in a closed drawer, it would not run), what is the most basic circuit I can construct? Can I still salvage my light-sensitive diodes or should I buy a different component?