Found in a 1924 Gernsback publication this circuit uses 4 batteries for power and loop antenna. Listening is over a high-impedance type earphone or loudspeaker common at the time.
This application consists of a circuit that trips when the sensor resistance drops below a few...
Small variations in the resistance of the subject's skin holding the test leads are detected by...
This circuit was found in documentation from the 70s. We can try current JFET transistors....