Found in American documentation from the 1980s, this circuit has a diode feedback. At the exit we have an indicator LED. The LM3900 is a transconductance operational amplifier.
This circuit is from an American publication from the 60's. The power is on the order of 600 mW....
Other operational amplifiers series, such as the MC34072, MC34074, MC35071, MC35072, MC35074 d...
Found in a European magazine from the 90s, this circuit emits beeps that are several seconds apart to...