Multifunctional environmentally friendly circuit

With the increase in industrial gas burning appliances, the presence of some flammable, explosive and harmful gases has become a problem that people cannot ignore. The multifunctional environmental protection
device has the functions of sound and light alarm for harmful gases, automatic ventilation and fresh air. The following is a brief introduction to its working principle.
． The circuit of the multifunctional environmental protection device is shown in Figure 7-18.
    (1) The gas-sensitive sound and light alarm outputs a DC voltage of 1ZV from the three-terminal voltage regulator 7812 to supply the heating electrode of the gas sensor QM-N5. QM-
N5 is very sensitive to coal gas, liquefied gas, carbon monoxide and smoke. When the concentration of harmful gases in the room increases to a certain level,
the conductivity between its A and B plates increases, causing the potential of point B to increase. The detection signal is delayed and added to VT1, causing VT1 to saturate and conduct. At this time, the ⑦ and
@ pins of NE555 change from high level to low level, and ③ pin outputs high level , so the light-emitting tube VD8 goes out and VD7 points Bright. At the same time, the relaxation oscillator composed of VF2 and others
starts to vibrate, and the piezoelectric sheet HTD emits a rhythmic alarm sound to complete the audible and visual alarm.
    (2) Automatic exhaust and ventilation. At the same time as the audible and visual alarm, the relay operates. At this time, the Kl suction table connected to the ventilation fan performs exhaust and ventilation.
On the contrary, when the concentration of harmful gases drops to a certain value, the ventilation fan will automatically power off and the audible and visual alarm will sound. :
    Generation of fresh air: Fresh air is produced by an open negative ion generator. At the same time as the relay operates, the K-2 suction
platform and the multivibrator mainly composed of VT3 are started. The secondary (side) rectifier of the transformer T outputs negative high voltage through rectification, and the air is ionized through discharge
. The generated air negative ions have the functions of capturing floating dust, sterilizing and neutralizing harmful gases, making the air fresh and beneficial to health.
The discharge end adopts an open multi-plate type to improve the transmission rate and diffusion area of ​​negative ions. -:-
    The characteristic of this multi-functional environmental protection device is that the circuit is relatively simple and the requirements for the components used are not high, but it has some good effects.