This circuit was obtained from a 90s Radio Electronics. The value of R1 determines the scale according to the table next to the diagram. The power suppley 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...