Combustible gas alarm circuit diagram 7812 7805 555
Posted on Mar 28, 2007 8978
As shown in FIG alarm by a buck rectifier and voltage regulator circuit, gas sensor, comparator circuit and sound the alarm circuit. Buck regulator circuit by a transformer rec
tifier and B, the bridge rectifier circuits QL, IC3 (7812), IC4 (7805) and other components. Gas-sensitive semiconductor sensor QM-N5-type or MQ-N-type devices. Comparator IC1 dual voltage comparator LM393. Audio alarm circuit consists of IC2 (555), speaker Y, LED and other components. When the concentration of flammable gas exceeds a certain value, between AB pole semiconductor gas device resistance becomes small, the partial pressure of the resistance R1 increases, the potential of the corresponding comparator IC1 foot rises, and when the above feet when the reference voltage value, IC1 output high, the 555 set, while 555 and R3, R4, C1 composed of the oscillator starts oscillation frequency f 1.44/(R3 + 2R4) C1, as shown in FIG. parameters corresponding to a frequency of about 1000Hz. 555 signal output pin push speaker Y issued lkHz sound alarm signal, and the LED lamp flashes. When the concentration of flammable gas is normal, between the AB QM-N5 resistance becomes very large, the partial pressure resistor R1 becomes smaller, the potential reduction of the corresponding IC1 foot, IC1 output low ( 0.7V), 555 Reset, the alarm circuit does not occur.The alarm circuit sends out the concentration of flammable gas is higher than 0.04% audible and visual alarm signals to alert the owner attention.