This simple sensitive circuit was suggested in a July 1992 Radio Electronics issue. The relay is a double-contact changeover relay. Sensitivity adjustment is made at R2.
This 50% duty cycle configuration was found in a Popular Electronics from the 1990s. The operating...
We found this circuit in an early American 80's documentation. We note that the first gate of the...
This circuit was found in the Linear Technology Applications of 1997. The circuit uses common...