For experiments with a disk rotating at various speeds, the April 1998 Electronics Now magazine suggests this PWM motor control. The current with the LM317 is 1.5A maximum.
This circuit is based on an operational window comparator. We found it in a documentation from the...
This excellent 3-transistor audio preamplifier is suitable for use with high-impedance...
This detector circuit can be used to check the operation of small transmitters or as an input step...