This small receiver for the medium wave range was found in Radio Electronics magazine from July 1958. The circuit is for listening to headphones and powered by batteries.
We have many versions of biofeedback with the 555 IC on this site. This is another one. We found it...
Using an operational amplifier of the time, this circuit was obtained from a 90s Radio...
This circuit was suggested by Popular Electronics from the 90s. The circuit is quite simple using...