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 was found in the December 1995 issue of Electronics Now magazine. The circuit...
In the figure we have the photo-conductive way of using a photocell to control a small motor with...
This circuit, which can be used on percussion instruments, has the oscillation point adjustment made in...