Found in an 80's Electronic Design, this circuit is based on the ICL7107 which is not an easy component to obtain today. The circuit is compatible with TTL and CMOS.
This circuit simulates a resistor controlled by digital signals. We found it in American...
Found in Popular Electronics this circuit will trigger a buzzer if the ignition key is removed...
We find this circuit in documentation from the 1980s. The triac and diac are of conventional types...