This circuit that we found in a 1990 documentation uses an LED as a sensor. The operational amplifier is equivalent to the 741 and the trigger adjustment is made in the potentiometer.
This circuit has both frequency and duty cycle control. We found it in the October 1992 Radio...
This power supply is indicated for the supply of not very powerful car radios of the AM and FM...
In the absence of a modulation signal, the carrier of this simple short-range transmitter is cut...