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.
The sound produced by this circuit, from a 1978 publication, depends on the humidity between the...
In a September 1992 Radio Electronics article, we found this basic 555 circuit used to generate fixed...
This circuit is suggested by Motorola, using a 4N26 type coupler and an MC1733 type operational....