Using 5 V relays, this circuit can be used as a control shield for microcontrollers. The circuit uses relays, and the motor voltage is independent of the control voltage.
This National Semiconductor circuit appears elsewhere on this site. The circuit must be powered by...
In this circuit the frequency is determined by the coil and the variable capacitor. Transistors like the...
This circuit is from old American documentation, but the transistor used is still very common...