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 found on a William Sheets can be used with a headphone or external amplifier. The...
In the figure we have the circuit of a complete audio generator using the 741. The circuit was found...
This monostable multivibrator with signals in phase opposition was found in October 1986 Radio...