Found in Ferranti's 1969 documentation, this circuit can be mounted with a modern equivalent transistor. The circuit has a 4 V immunity and can be used as a shield for sensors.
We found this heart rate sensor circuit in a Popular Electronics from the 90s. The placement of...
Based on an LM317T, this circuit found in Popular Electronics works with signals of frequencies up to...
The circuit shown is from a 1972 publication. Transistors can be current types like 2N2222. The...