Ventilator auto-control circuit composed of μA555

Published:2011/10/20 20:58:00 Author:Rebekka | Keyword: Ventilator auto-control | From:SeekIC

The circuit is composed of the AC step-down rectifier (VDD = +9 V), toxic and hazardous gas sensor head QM-N5, the temperature detection circuit Rt, bistable control circuit. QM-N5 is a gas sensory semiconductor device, Rt uses MF-51 NTC thermistor. The resistance at the 2 ends of QM between A and B is larger. The potential of B is lower than 1V. It makes the D2, BG2 stop. 555 feet will be reset by the high level of ⑥. The low level output by pin ③ will stop SCR. The ventilation fan does not work. When the concentrations of indoor harmful gases exceeds the allowable value, the resistance value of QM-N5 will rapidly decrease and the electric potential of B rises, the D2, BG2 will be conducted.



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