This circuit was found in a documentation of the 80s, having didactic purpose. For R1 values between 10k to 1M can be used. Transistors are general purpose types.
This low noise circuit was obtained from a 1980s US RF publication. Transistors used are uncommon...
IDT ZSSC3230 Capacitive Sensor Signal Conditioner Available from Mouser Electronics stock, this IDT...
We found this car theft alarm circuit in a 1988 publication, but the components used can still be...