This sensitive circuit was found in the June 1995 Electronics Now magazine. R1 can be from 10k to 1M depending on the desired sensitivity. Power is supplied by the relay.
We present a circuit formed by six voltage comparators. Each comparator will analyze the voltage...
This circuit can generate time base signals from 5 to 1500 Hz. We find it in a documentation about old neon...
In this circuit the CA3140, an operational amplifier, is used as a comparator with the zener diode...