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 is from 1990 documentation. It uses a bridge with LEDs and the potentiometer must be...
This circuit has the spark duration controlled by a 555 timer. The circuit was found in the 1990...
Taking Raytheon's 3900 integrated circuits as an example, uncommon today, this circuit can be used...