This assembly is from 1957 from a Raytheon manual, but can be modernized using a BC548, 6 V power supply and common 100 mA relays.
With this circuit it is possible to fire an SCR from the light that falls on a phototransistor. The circuit...
This simple circuit can use any general-purpose transistor. The power supply must be isolated. The circuit...
Using a sensor from the time, this circuit was found in the 1992 Radio Electronics Handbook...