The frequency of this circuit depends on C1 and, for the indicated values, it is 1 kHz. Equivalent operational amplifiers can be used, and the power supply must be symmetrical.
Found in a 90s Popular Electronics, this circuit triggers a load from the audio signal applied to...
This circuit generates alternating magnetic fields in a small electromagnet for various...
This dimmer, from an old publication, can use almost any triac and in shooting a neon lamp. The...