This circuit for low frequency data transmission was found in the May 1977 issue of Radio Electronics magazine. The circuit modulates the signal at two frequencies for bits 0 and 1.
This 1995 circuit uses interruption sensors or NC connected in series in any quantity. With the...
This circuit transmits the audio signals from a telephone line to an FM receiver placed nearby. The...
This circuit is from an old manual of operational amplifiers. The setting can be adapted to work...