The circuit shown is from a 1994 National Semiconductor documentation and 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...