This circuit was found in a documentation of the 80s, having didactic purpose. For R1 values between 10k to 1M can be used. Transistors are general purpose types.
This interesting logic circuit was found in a manual of neon lamp applications. | Clique na imagem...
This circuit uses a sensitive reed relay to control external loads. The time delay is given by the...
This circuit for PC and which can also be used with microcontrollers was found in an English...