Using an analog microamperimeter this circuit has a phototransistor adapted to the wheel as a sensor. The circuit is from American documentation from the 1980s, but the components are common today.
This circuit drives symmetrical loads through a single transistor. The circuit is from a Radio...
The transistors of this circuit can be BC548 for NPN and BD136 for PNP with load up to 500 mA. The...
circuit is used to increase the sensivity of a relay. A 50 to 100 mA relay can be triggered with...