PM2.5 monitoring equipment system circuit module design

　　This detection equipment PM2.5 environmental monitoring system is inexpensive and can solve the problem of capital investment. In the monitoring area, the PM2.5 detection of each node is composed of PM2.5 sensors and detection boards, and the data is transmitted to the cloud monitoring center through wireless communication. Among the wireless long-distance data transmission methods, the general packet radio service (GPRS) provides an efficient and low-cost way for remote monitoring data transmission. Users are charged according to traffic online, which greatly reduces the operating cost of the system. The global wireless access to the Internet provided by GPRS makes data transmission via GPRS and the Internet faster and more efficient.

　　Clock circuit

　　The internal clock mode is used in the figure, that is, the internal oscillator circuit of the chip is used. When the timing element is connected to the pins of XTAL1 and XTAL2, the internal oscillator can generate self-excited oscillation. Generally speaking, the crystal oscillator can be selected between 1.2 and 12MHz, and can even reach 24MHz or higher, but the higher the frequency, the greater the power consumption. The 11.0592M quartz crystal oscillator used in this experimental kit. The size of the two capacitors connected in parallel with the crystal oscillator has a slight effect on the oscillation frequency and can play a role in fine-tuning the frequency. When using a quartz crystal oscillator, the capacitor can be selected between 20 and 40pF (30pF is used in this experimental kit); when using a ceramic resonant device, the capacitor should be appropriately increased to between 30 and 50pF. Usually, a 33pF ceramic capacitor is sufficient. It is also worth mentioning that if the reader designs the printed circuit board of the microcontroller system by himself, the crystal and capacitor should be as close to the microcontroller chip as possible to reduce the parasitic capacitance of the lead and ensure the reliable operation of the oscillator. To check whether the crystal oscillator is oscillating, you can use an oscilloscope to observe the beautiful sine wave output by XTAL2, or you can use a multimeter to measure (set the gear to DC, then the effective value is measured). When measuring the voltage between XTAL2 and ground, you can see a voltage of about 2V.

　　Reset Circuit

　　In the single-chip microcomputer system, the reset circuit is very critical. When the program runs away or crashes, it needs to be reset. When the reset pin RST of the MCS-5l series single-chip microcomputer appears high level for more than 2 machine cycles, the single-chip microcomputer performs the reset operation. If RST continues to be high level, the single-chip microcomputer is in a cyclic reset state. Reset operation usually has two basic forms: power-on automatic reset and switch reset. At the moment of power-on, the voltage across the capacitor cannot change suddenly. At this time, the negative pole of the capacitor is connected to RESET, and the voltage is all added to the resistor. The input of RESET is high, and the chip is reset. Then the +5V power supply charges the capacitor, and the voltage on the resistor gradually decreases, and finally equals to 0, and the chip works normally. The reset button is connected in parallel to both ends of the capacitor. When the reset button is not pressed, the circuit realizes power-on reset. After the chip works normally, the RST pin is pressed to make a high level to achieve the effect of manual reset. P0 port external pull-up resistor 51 The P0 port of the single-chip microcomputer is an open-drain output, and there is no internal pull-up resistor. Therefore, when used as a normal I/O to output data, since V2 is cut off, the output stage is an open-drain circuit. In order to output the "1" signal (i.e. high level) normally, an external pull-up resistor must be connected, as shown in the figure.

　　LCD12864 Display Module

　　Based on the large amount of information displayed in this design, this design chooses LCD12864 liquid crystal display screen with large amount of liquid crystal information display, low power consumption, small size, light weight, ultra-thin and other functions as the component to realize the display function. FYD12864-0402B is a dot matrix graphic LCD display module with multiple interface modes of 4-bit/8-bit parallel, 2-wire or 3-wire serial, and internally contains national standard first-level and second-level simplified Chinese character libraries; its display resolution is 128×64, with 8192 16*16 dot Chinese characters and 128 16*8 dot ASCII character sets built in. Using the flexible interface mode and simple and convenient operation instructions of this module, a full Chinese human-computer interactive graphical interface can be constructed. It can display 8×4 lines of 16×16 dot matrix Chinese characters. Graphic display can also be completed.

　　Buzzer alarm module

　　The monitoring values ​​collected by the temperature and humidity sensor are transmitted to the single-chip microcomputer. When the single-chip microcomputer compares and monitors values ​​that exceed the set threshold, the fan is driven. If the cooling effect of the fan is lower than the speed of temperature increase, when the temperature exceeds the set maximum temperature limit, the buzzer starts to work and alarms until the temperature reaches the safe temperature range and stops beeping and alarming. Similarly, when the humidity reaches the set maximum humidity limit, the buzzer also starts to work and alarms until the humidity reaches the normal humidity range and stops beeping and alarming.

　　Temperature and humidity control module

　　Temperature and humidity regulation is mainly divided into heating module, cooling module, drying module and humidification module. The temperature and humidity regulation of the system is realized by controlling the electric heater to heat up, the fan to cool down, and the humidifier to humidify the air through the single-chip microcomputer. This design mainly realizes the fan cooling function. The main component of the cooling module is composed of a small motor, which is cut into a fan blade shape with plastic sheets and installed on the small motor. When the current temperature measured by the temperature and humidity sensor is higher than the set limit value, the system automatically starts the small motor to cool down until the temperature returns to the normal value range. The system automatically stops the rotation of the motor to adjust the temperature and refrigerate.

　　The AT89C52 single-chip microcomputer is used as the control center, the DSM501 dust sensor measures the air dust concentration, and the LCD12864 display shows the current air dust concentration. When the dust concentration in the air reaches the set limit, the buzzer automatically alarms. Practice has proved that the system has a simple circuit, stable operation, high integration, convenient debugging, high test accuracy, and has certain practical value.