Simple infrared fire alarm circuit

The fire alarm integrated circuit MC145012 integrates all the functions of the alarm. As long as external infrared transmitting and receiving components and speakers are connected, a fire alarm can be formed, and it can also be connected to a computer to form an alarm system.
Circuit Principles. The infrared LED is driven by the ⑥ pin output (LED (Light-Emitting-Diode in Chinese means light-emitting diode) is a semiconductor that can convert electrical energy into visible light. It changes the principle of incandescent lamp tungsten filament luminescence and energy-saving lamp three-primary color powder luminescence. , and uses electric field luminescence. According to analysis, the characteristics of LED are very obvious, such as long life, high luminous efficiency, no radiation and low power consumption. The spectrum of LED is almost entirely concentrated in the visible light band, and its luminous efficiency can exceed 150lm/W (2010 ). ) (D3) emits infrared light and is received by the infrared receiving tube D2: D2 and D3 are installed in a position where they cannot directly illuminate each other. When there is no smoke caused by fire, the D2 output is 0; if there is smoke, the infrared light is scattered by the smoke, so that D2 can receive the scattered light and trigger the alarm.
In Figure 2, adjusting the values ​​of C2 and R13 can coarsely adjust the detection sensitivity; VB1 is the fine adjustment of the sensitivity; SW1 is the start button; the speaker uses a piezoelectric speaker; ⑦ pin is the I/O port, used to connect to external control circuits such as computers. .
The whole machine is powered by a 9V battery. When using manganese-zinc batteries, C4 is 22μF. When using alkaline batteries, C4 is 1μF.