Found in a 70s RCA transistor manual, this circuit is recommended for mass-positive cars of the era. The transistor is for general use.
Approaching the hand or an object to the sensor of this circuit, the relay closes its contacts. The...
For those who want to recover an old multimeter of this type, the circuit presented is worth...
The circuit shown is only for analog telephone lines. I found it in Popular Electronics (1991). It...