This circuit was found in an English magazine from 1977. Signal inputs and outputs must be shielded, and the circuit can be powered by battery, since its consumption is low.
This circuit is from a documentation from the 70s. The transistors are types of germanium of the...
We found this heart rate sensor circuit in a Popular Electronics from the 90s. The placement of...
This circuit from a 1966 General Electric manual makes use of an SCS. The time is given by the...