This circuit generates short pulses. The transistor can be a 2N2222 or BC548 and the frequency is given by the resistors and the capacitor that can be changed.
The integrated circuit used in this project is not common today, but it can be implemented with more...
Found in an American publication from 1969, this circuit can be adapted to be used as a shield....
This current meter with many scales was found in a 80s American documentation. The operational amplifier...