The Monitoring and Wireless Transmission System of PM2.5 in the Scenic

The system based on 89C51 single chip is composed of the data acquisition module, the key circuit, the alarm module and the GSM wireless transmission module. The structure of the system is shown in Figure 1.

Figure 1.

As shown in Figure 1, the system can collect the PM2.5 and the temperature data in a certain area through the dust particle sensor and the temperature sensor. Because the analog signal could not processed by the MCU, so using DS1820 AD conversion module to convert the analog signal to the digital signal and then transmit the data to the MCU and displayed on the LCD screen. At the same time, the MCU compares the collected data with the threshold, if the collected value is higher than the threshold, the buzzer will alarm and send the PM2.5 concentration and the current temperature information to the user with the short message[4].

The selection of the PM2.5 dust sensor affects the range and precision of the monitoring module directly. GP2Y1010AU0F dust concentration sensor was used in this paper. From Table 1, the working voltage of the dust concentration sensor module is the same with the single chip. Its high accuracy meets the requirements of the majority of users. The large temperature range can be applied to all kinds of bad environment. In general, more than 120mg/m3 of PM2.5 can cause harm to the human body, so this module’s range is sufficient.

TABLE 1.

Dust sensor is used to measure the dust concentration in the air by the reflection principle of dust. The internal structure of the dust concentration sensor is shown in Figure 2.

Figure 2.

The function and pin of the dust sensor is shown in Table 2. With the received pulse signal and the output voltage signal from the single chip, the dust sensor controls the receiving device PD (photo detector). The sending device IRED (infrared light emitting diode) feeds the MCU with the dust concentration in the form of voltage. There are two transistors IRED and PD inside the dust sensor. The IRED emits the light and the PD receives the light signals reflected back by the dust. When the module works normally, the IRED emits the light. If the dust particle is enough, the reflected light will received by PD, the intensity of the light signal will change the PD voltage. Then with the higher output voltage of the dust particles, the concentration of PM2.5 becomes higher.

TABLE 2.

A DSl820 digital thermometer provides nine bits (binary) temperature readings and the single chip can communicate with DS1802. Each DS1802 has a specific sequence number. Multiple DS1820 can work on the same bus without worrying lack of the bus. The pin of the DS1820 is shown in Figure 3:

Figure 3.

The measurement range of the DSl820 from -55°C to 125°C. Two eight bits temperature values were stored. The DS1820 has two power supply mode: data bus power supply mode and external power supply mode. The first mode uses less wire but less efficiency. The latter used a single wire but faster. The DS1820 interface specifications: pin one is the ground; pin two connects the single chip P2 for data transmission; pin three connects VCC.

DS1820 stored the with the nine bits temperature value. The highest bit is the symbol bit. The temperature storage of DS1820 is shown in Table 3. When the temperature is negative S=1, when it is positive S=0. Such as: 00AAH indicates +85°C, 0032H is 25 °C and FF92H is -55°C.

TABLE 3.

GSM (Global system of mobile) is the second generation of the mobile communication technology. It promotes the globalization of the world and makes the users use one mobile phone to communicate around the world. So they produced a unified standard of the mobile phone network, namely the GSM. GSM wireless communication module adopts the SIMCOM’s SIM900A module to realize the function of the short message.

The SIM900A module supports most 3G or 4G mobile communications services. The TTL serial port and the RS232 module can be used for debugging. The SIM900A module has the function of the power self-starter. Firstly, the SIM card is placed in the slot and then the working mode of the SIM900A is shown in Table 4:

TABLE 4.

GSM module realizes the function of SMS through SIM900A chip controlling the SIM card module and other modules. Nowadays it is widely used in China.

At first, the system initializes the flash, the port and the LCD etc[5]. Then the sensor begins work and the data collection is achieved. After the AD0832 converted, the data is displayed on the LCD1602. At this time, if the data is higher than the threshold, the buzzer alarms and the data is sent to the user’s mobile phone through the GSM wireless transmission module to complete the alarm function[6]. The software process is shown in Figure 4.

Figure 4.

The data collection of the dust concentration is the key of the software programming. The data collection and processing of PM2.5 concentration is introduced in Figure 5.

Figure 5.

When the power turns on, the dust monitoring sensor initializes[7]. Then the PM2.5 sensor is waiting for the instruction from the MCU. When it receives the instruction, the sensor turns on the IRED to data acquisition, PD (photo detector) will receive the reflected light signal, and the light intensity will affect the voltage across the PD, which is sent to the MCU[8]. After received the voltage signal, the MCU controls AD0832 begin A/D conversion and the collected information send to the LCD1602, so the data acquisition is completed.

The DS1820 temperature sensor collects the temperature and returns the digital information[9]. As shown in Figure 6, After initialization, the sensor reads the data in ROM: the serial number and the temperature information of DS1820[10]. The general delay 1s can read the temperature information, and then the pointer in the buffer is added to the next data reading[11].

Figure 6.