This optically coupled circuit was found in the February 1968 Radio Electronics magazine. The circuit uses an LDR in modulation. Transistors are types of the time.
This circuit uses unijunction transistors and drives a small speaker through an output...
This interesting game was found in a 1987 publication, but it is very simple and can be easily...
This circuit uses a thermistor or NTC as a temperature sensor and provides the indication on an...