This circuit uses a parallel resonant crystal to control the frequency. The circuit is from Radio Electronics magazine, February 1993. Equivalent transistors can be used.
This circuit is of an old Argentine magazine of the 70's. The difficulty for its assembly is in...
This passive circuit was found in a 1980s documentation. The circuit serves to indicate the...
In the figure we have the way to implement a monostable with an operational amplifier LM393. The...