This circuit is from an old American documentation from the 70s. Transistor 2N3904 can be replaced by BC548. The relay must have 100 mA of maximum current.
The circuit, shown in the figure, activates a relay when the logic level applied to its input, from...
The traditional circuit was taken from a French magazine Radio Plans that no longer exists but can...
This circuit makes use of the LM11, 112 or 113 operatives and was found in a 1980s documentation. The...