Any sensor or piezo capsule can be used as a sensor in this circuit. The integrated circuit is also common in our days and a table of sensor voltage levels.
Found in an old publication, this is a transmitter with a spark coil. The high frequency...
This circuit was found in a 90s Hands-On Electronics. When a signal appears at the headphone...
In the figure we give a suggestion of a high-power stage to excite a speaker with the 2N3055. The...