We found this configuration in a 1990 Poptronics. The circuit can be powered by voltages between 6 and 15 V, changing the resistors in series with the LED. The frequency is set at R7.
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...