This circuit can activate a powerful lamp or call system when a telephone call occurs. Suitable for hearing impaired or noisy places it was found in American documentation in the 90s.
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...