This circuit can use a pendulum sensor. We found this configuration in a 1994 publication. The components used are common and the timing is given by the capacitor C1 which can be changed.
In the figure we have the typical configuration of a sinusoidal audio oscillator with twin-T. The...
This timer was found in English documentation from the 80's. The integrated circuit is common...
This circuit for monitoring telegraphy transmissions was found in a 1975 CQ magazine. Transistors may be...