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 crystal configuration can be made with triggers of any logic. The frequency is given by the...
This circuit was obtained from an 80s factory manual. The integrated circuits used are uncommon...
We found this circuit in an old American documentation. It is an electronic rheostat with a...