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.
The circuit that gave rise to this configuration is from 1978. In the original publication are...
We found this circuit in Popular Electronics from 1992. Time is given by C1. The circuit provides an...
This circuit was obtained in a 1980 publication but can still be assembled today with the 106...