The circuit is from the 1994 National Semiconductor Linear Applications Handbook but can be implemented with more modern operational amplifiers. The power supply must be symmetrical.
Today we can call this circuit a baby monitor. It is a microphone amplifier found in a publication by...
Found in Motorola documentation from the 90's, this circuit charges the capacitor with a constant...
This small transmitter can send its signals to a receiver placed at distances up to 100 m. The...