The integrated circuit used in this 2002 project is not very common. It is powered directly by the telephone line, requiring no power supply.
This circuit simulates a resistor controlled by digital signals. We found it in American...
This 1968 Texas Instruments circuit uses diacs of the era. SCRs can be modern equivalents according...
This simple continuity tester consists of an oscillator found in the 1983 Electronics Experimenter Special...