The circuit shown consists of a power stage for relay excitation. 2N3053 can be a BD135 and 2N406 can be replaced with a BD136. R3 depends on the trigger voltage.
This circuit is based on the voltage drop of the diodes in conduction, in the order of 1.6 to 1.7...
Found in older documentation this setting applies to modern components, noting that the power...
This simple timer can be used in many applications such as egg timer. The LED glows up when S1 is...