This circuit was found in a Popular Electronics from the 90's. The transistors are general-purpose types and the loaded load depends on the voltage and must have a maximum current of 100 mA.
This circuit is of great use today, when solar energy is becoming increasingly important. The...
In figure we have an interesting circuit in which an LED is used as a photoelectric sensor. When...
This circuit is from an old English documentation. It is intended for coupling a microphone to the...