How to Build Toxic Gas Detector and Alarm Circuit with TGS813

The danger always exists, when the fuel gases such as propane or gas are confined to a small area. The alarm of toxic gases figs. 1-45 utilizes a tin-oxide-semiconductor. A coil of thin wire heated by a battery 12 V via IC1 and IC2, which pulses the voltage to the coil of the sensor, saving a significant amount of energy. Diode Zener Dl provides a constant voltage to the filament coil sensor. resistance of the sensor reduces the sensor is exposed to toxic gases such as hydrogen, carbon

Carbon monoxide and propane. To reduce 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 switch 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. R7 sensitivity control set to the desired value, before the activation of SCR.

How to Build Toxic Gas Detector and Alarm Circuit with TGS813

The toxic gas alarm 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.

Part List
Part Description
C1 0,01-MFD, 25-V capacitor (disc)
1 9-V zener diode D1 (NTE139A)
1 D2 4-V diode zener (NTE5068A)
1 SCR D3 (NTE5408)
1 Q1 Transistor 2N2222
U1 1 CD4013 CMOS flip-flop
1 U2 CD4049 CMOS Inverter Hex
1 siren piezo BUZ 6-9V
1 S1-TGS203 toxic gas sensor (Figaro or equivalent)


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