Found in documentation from the 1980s, this circuit can have several adaptations to use modern transistors and LEDs instead of the lamp. The power supply voltage can also be changed.
In the figure we have a regulator circuit for output voltages of 0.5 to 10 V with currents up to...
Found in American documentation from 1968, this circuit has an acute cut-off of the frequency to...
When a model train crosses a level crossing, interrupting the light on the sensor, this circuit...