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 obtained from a 1977 magazine, but can still be mounted using BC548 for TR1 and...
We found this circuit in a European publication from the 1990s. Transistors are still common types...
The figure shows how to add a Darlington stage to an operational amplifier in order to obtain a...