This simple logic test circuit with 3 LEDs was found in October 1985 Radio Electronics magazine. The power supply is according to the logic, and this version is indicated for TTL.
The circuit shown is from an old European publication. In it we have the way to activate a relay...
We found this circuit in a European publication from the 1990s. Transistors are still common types...
This circuit was found in an American documentation and can be added to common amplifiers of any...