This circuit was obtained in an Electronics Now from the 90s. The circuit uses operational amplifiers from the time and the indicator is of the Sonalert type with internal oscillator.
This simple alarm circuit was found in a 1998 documentation. When the sensors are activated, the...
This circuit was found in an old American documentation. The integrated circuit used is uncommon...
Found in a 90s Electronic Design, this suggestion to have a higher voltage in a fixed regulator...