Wiring Schematic Diagram

This toxic gas alarm circuit is sensitive to less than 100 ppm of carbon monoxide. This alarm is useful for simple gas boats, sheds and cabins. You could save a life. Some of the companies listed in the Appendix to offer plans and kits for various toxic gas sensors.

Alarm of toxic gases it utilizes a tin-oxide-semiconductor. A coil of thin wire heated by a battery 12 V via IC1 and IC2, the which pulses the voltage to the coil of the sensor, saving a significant amount of energy. Zener diode Dl provides a constant voltage to the filament coil sensors. resistance of the sensor reduces the sensor is exposed to toxic gases Such as hydrogen, carbon monoxide and propane. Reduced to the resistance of the sensor, the SCR gate voltage increases. When the gate threshold voltage is reached, the SCR fires and a buzzer alarm is activated. Once activated, the bell and the switches S1 Should Be used to reset the alarm. Since the sensor has a good deal of thermal inertia, S1 must be off or open for about three or four minutes after the initial activation, allowing the sensor to stabilize, thus avoiding false alarms. Sensitivity control R7 set to the Desired value, before the activation of the SCR.

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