This traditional configuration found in a Radio Shack document can use 2N2646. More keys can be added, and the power can be supplied with voltages from 9 to 15 V.
Using the 709 integrated circuit, one of the first operational, this circuit was found in the...
The circuit presented generates pulses at regular intervals with the duration controlled by a...
Found in a 1966 documentation, this circuit monitors the operation of an air conditioning system....