Sensors and Detectors:
Gas/Vapor/Smoke/Flame Detectors

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.

Gas Sensor - All-in-one (with a sensor and a temperature compensation device)

Flame/Smoke Detector - Flame, gas and smoke detector for fire alarm. You can combine this circuit with alarm circuit. The output will be the relay which switch on and switch off the alarm.