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.
Suggested by a 90’s Radio Electronics, this circuit automatically activates the recording switch of an...
Found in a 1960s Electronic Design, this circuit provides a signal from the sensing of an analog...
Operating at a frequency of around 180 kHz, this transmitter was found in a Science & Electronics...