Found in an Electronic Design and 1970s, this circuit uses transistors of the time. The transistors can be replaced with equivalents and the relay is 12 V depending on the power supply.
This circuit, which can also be adapted to function as a microcontroller shield, is from 2003...
This sensitive circuit was found in an Electronics Hobbyists Handbook from the 1990s. The circuit can...
This circuit can be used with 3 receivers and is intended for low frequencies (medium wave range). We...