We have many versions of biofeedback with the 555 IC on this site. This is another one. We found it in October 1986 Radio Radio Electronics magazine. The power supply must be isolated.
This oscillator uses a small IF transformer taken from an old transistor radio. FET admits...
This voltage-controlled oscillator uses an integrated circuit not common today. It can generate...
This circuit was found in Delco documentation from 1965. The transistor is of the time, but any...