This circuit uses a 555 (according to the diagram) to generate 50 ms tone bursts at a frequency of 1.5 kHz. The circuit is from an 80's Electronic Design.
This voltage controlled oscillator uses a varicap to change the frequency. Usin a 100 turns coil...
This circuit was obtained in a documentation from the National Bureau of Standards of 1968. The...
This circuit turns on your car's backlight when a vehicle coming from behind gets too close to it...