This low frequency oscillator circuit was found in an Electronic Design from the 90s. The transistors are common types, and the frequency is given by the crystal.
This is the normal configuration for the TDA2003 integrated circuit, an amplifier that can provide 10...
Found in an English publication from 1977, this circuit uses only 1 LED. Unlit means heads and lit...
In the figure we have the transmitter and the receiver for an optical audio link via infrared. The...