Originally suggested by Harris in the 1990s, this circuit uses an optical tachometer. The circuit is for 12 V motors.
With this configuration we have a voltage follower, amplifier with unit gain, in which the output...
This circuit that draws 1 out of 8 LEDs was found in an 80's American documentation. The circuit...
The transistors in this circuit can be the BC548 and a small speaker serves as a microphone. The...