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.
In the figure we have a way of receiving ultrasonic signals of a single frequency using a PLL 567....
The HA2620 integrated circuit used in this comparator is from the 80's, but the setting can be...
The UM3562 integrated circuit (not very easy to find) synthesizes three types of sound that...