This is the receiver circuit for the transmitter of the previous circuit using an integrated circuit of the time. The circuit is in the same Radio Electronics magazine as August 1986.
Frequencies up to just over 100 kHz can be obtained with an oscillator based on one of the four...
This circuit, found in a Popular Electronics from 1992, is based on an oscillator and a crystal...
This is a discrete equivalent version of an open collector TTL gate. What we have is an inverter...