Found in a 90s Popular Electronics, this circuit is based on a common CMOS component. The circuit triggers a buzzer by approaching objects from an antenna.
This simple robot or motor control circuit using a photocell as a sensor was found in the magazine...
This circuit uses an operational amplifier to modulate the light emitted by an LED with audio...
Equivalent transistors, such as the BC548, can be used in this circuit that we find in...