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.
This circuit was obtained from a 1965 Radio Electronics. The semiconductors used admit modern...
In the bridged configuration the TDA2002 amplifier can supply 30 W of power at a load of 4 ohms...
This circuit converts a high voltage into a frequency using an optical coupler. The transistor can be 2N2646...