This double tone generator uses a specific integrated circuit, having been found in a 1977 CMOS Cookbook. The transistors can be the BC548.
This is a project that can easily be adapted for other purposes such as counting people, objects,...
This circuit is from a PopularElectronics of June 1992. The magazine no longer exists, but the...
This circuit makes use of a mechanical delay line to produce the reverberation effect. This is a...