This circuit was submitted by Adam from Canada who is still at school. I have provided the
text. The two transistors are used as a direct coupled switch, Adam used 2SC711 but any
general purpose transistor will do e.g. 2N3904, BC109C.
The CDS photocell, type ORP12 is normally illuminated, therefore its resistance is low. The
50k control, the 1k resistor and the photocell form a potential divider which biases the first
transistor. This transistor is on, its collector being held low,