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 simple version of a function generator with the XR2206 was found in the May 1977 issue of...
In a modern version this circuit can use an LED in series with a resistor in place of the lamp. The...
This VFO was found in a 1980s documentation. The central frequency is given by the crystal and the...