Found in 90s Popular Electronics, this circuit fires a load through a MOSFET from an audio signal applied to the input. Power supply is done according to the load.
The circuit with a common operational amplifier uses a zener as a reference. The circuit is from...
This is the normal circuit of a relaxation oscillator using an unijunction transistor such as the...
This CMOS version of the force gauge was found in a 1983 publication. In the CMOS version, the...