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.
We found this circuit in the 1994 Linear Applications Handbook from National Semiconductor. The...
This circuit is from an Electronics World of 1968. The transistors are of the time and the power...
This circuit checks the infrared emission of a common remote control. We found it in the March 1993...