This old 4-channel circuit was found in the December 1994 Electronics Now magazine. The circuit uses a 556 as a modulator. Note the code programming key.
This circuit was found in a 1966 EEE. What it does is it converts the logic levels of 0 V and +4 V...
This circuit has been found in operational documentation of the 1970s. The circuit has a fail-safe...
This simple circuit does not use active components and uses a small speaker as a microphone. The...