We found this code key or coded keyboard in a publication from the 90s. The circuit uses components that are still common today and is powered by a 12 V voltage according to the relay used.
This circuit was found in Texas Instruments documentation from the 1980s. The circuit has a Q less...
This circuit is from an English publication from 1978. The operational admits equivalents and the...
P1 on this Radio Shack circuit is a 6 V lamp with current up to 500 mA depending on Q2. The...