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.
We found this circuit in a 1994 publication. It uses common components and can measure frequencies from 0...
This circuit was suggested by Sprague Electric in an 80's documentation. The circuit uses a...
This interesting circuit appeared in the April 1952 Radio Electronics magazine. The circuit is...