This circuit was found in a 1969 Motorola documentation. The FET admits an equivalent. The circuit has high input impedance and is powered by voltages from 6 to 30 V.
We found this heart rate sensor circuit in a Popular Electronics from the 90s. The placement of...
This circuit, found in an old magazine of the year 1968, uses a Power germanium transistor. This...
This project came out in an article of mine (Newton C. Braga) in the Popular Electronics magazine of...