According to ZigBee's automotive air conditioning control system design strategy
According to ZigBee's automotive air conditioning control system design strategy Abstract: Aiming at the real-time requirements of automotive air-conditioning system, an automotive air-conditioning control system based on ZigBee technology is proposed. The network structure of the control system, sensor nodes and main circuit of the system are given. The network protocol and sensors of the control system are designed. The program flow of the node and the main control node. Provides a new technology for automobile air conditioning control. Automobile air-conditioning system is a special device that realizes the adjustment of the air environment inside the vehicle, and is used to meet the requirements of the passengers on the comfort of the vehicle [1]. The comfort of the occupants in the car is related to many factors such as the relative humidity, temperature, air flow rate, and surface temperature of the objects in the car [2]. Therefore, the automotive air conditioning system needs to perceive various environmental parameters inside and outside the car, and adjust accordingly according to the requirements. The automotive air conditioning system is affected by factors such as vehicle space and vehicle operating conditions, and works in a harsh environment with a large workload. Therefore, it requires high anti-interference and stability of the control system. Generally, traditional automobile air-conditioning systems are controlled by manual or automatic methods, and the control lines of these control methods are all connected by wire. Due to many air-conditioning control functions, complex system control lines, and low control accuracy, and the disadvantages of high cost, complicated monitoring system, and poor anti-interference, the feasibility and control accuracy of the air-conditioning control system are still greatly affected . ZigBee technology [3] is an emerging smart sensor and control technology, which is a combination of sensor technology and wireless network technology, and is widely used in environmental monitoring and industrial control. Because of its low cost, small size, strong real-time performance, low power consumption, strong anti-interference, good embeddability, etc. [4], it is especially suitable for harsh working sites, small data transmission volume, strong real-time performance, short transmission distance And the wiring is inconvenient. In the automotive air-conditioning control system, the ZigBee technology is used to collect and transmit the environmental parameters of the air-conditioning system, and the transmission and control of the control signals, to avoid the interference and influence of the harsh industrial site environment on the wired transmission method (such as electromagnetic interference, humidity, vibration Etc.), which improves the reliability and anti-interference ability of the control system, and has certain significance for reducing the energy consumption of the automobile air-conditioning system and improving the passenger comfort. In this paper, a vehicle air-conditioning control system based on ZigBee is designed, which greatly reduces the cost and complexity of the control system, reduces the energy consumption of the system, and improves the control accuracy and feasibility of the system. 1 System design 1.1 Control system design The principle of the automobile air-conditioning control system is shown in Figure 1. The system consists of sensor nodes, system main control nodes, and action nodes. Sensor nodes include nodes such as temperature and humidity sensors inside the car, temperature sensors outside the car, CO2 concentration sensors, light sensors, and various damper sensors. Action control nodes include compressor control nodes, blower control nodes, defrost dampers, mixed damper circulation dampers and other damper control nodes, warm water valves and humidifier control nodes. The system will process the monitored temperature, humidity, CO2 concentration inside and outside the vehicle data through the processing of the sensor node, convert it into a digital signal and send it to the main control node. The main node will process it accordingly, and then send the corresponding instructions to the action node To keep the temperature, humidity and air quality in the car within the set range. 1.2 System circuit design The circuit design of the automotive air-conditioning control system includes: (1) Environmental data collection circuit, including interior temperature, humidity and CO2 concentration collection nodes, light collection nodes, exterior temperature collection nodes, damper position detection nodes, etc .; (2) air conditioning system work And control circuits, including compressor operation control node, evaporator and condenser fan control node, damper position control node, defrost control node, humidification control node, heating control node and other circuits; (3) Main control node circuit, mainly including Control and display circuits, operation control circuits, etc. The basic circuit of the environmental parameter sensor in the vehicle is shown in Figure 3. The sensor circuit is composed of CO2 concentration sensor, signal amplification circuit, temperature and humidity sensor, power supply circuit, CC2430 processor and so on. The power supply voltage is 5 V and 3 V, respectively. The CO2 concentration detection uses the TGS4161 sensor, which has the characteristics of small size, long life, good selectivity and stability, and also has the characteristics of high humidity and low temperature resistance. It can be widely used in automatic ventilation systems or for CO2 gas. Long-term monitoring and other applications [5]. The weak voltage output by the CO2 sensor is amplified by the amplifier U3 (LM386) and output to P0_2 of U5 for A / D conversion and stored in the storage unit specified by CC2430. PR1 adjusts the gain of the amplifier so that the concentration output signal voltage varies between 0 and 3 V. In order to keep the sensor at the most sensitive temperature, the heater needs to be supplied with a heating voltage for heating. The basic circuits of the evaporator, condenser, ventilation fan motor and compressor control node are shown in Figure 4. After U2 receives the control signal from the main controller, it calls the motor speed interruption program in the processor, and outputs a certain duty cycle control signal from P0_0 through the optocoupler U3 to control the conduction current of Q1 to control the air supply. The speed of the motor. 2 System software design 2.1 Network protocol and data frame design Through the analysis of the application of this system, in order to save the program storage space of the node, the ZigBee protocol has been simplified. The security mechanism is omitted in the system protocol. The device type of the FFD node is set to a full-function node with no security mechanism (FFDNS [5]), and the device type of the RFD node is a simplified function node with no security mechanism (RFDNS). Primitives unrelated to this application are omitted to improve protocol efficiency. Sensor and control node protocol and implementation primitives are shown in Figure 6. The data frame format for system data transmission uses ZigBee's MAC layer packet format [6], and its structure is shown in Figure 7. The definition of the frame load in the data packet is: slave node number + node type + detection parameter (or action instruction), where the slave node number is bound to the sensor or control node ID. Figure 7 Digital frame structure 2.2 System software design The control system programming uses a modular programming method, which is composed of a main control module and a wireless node module. The system software flow is shown in Figure 8, and the wireless network node flow chart is shown in Figure 9. 3 System test results and discussion After the design of each node of the system was completed, the system designed in this article was tested in a certain type of CMB bus. The test results are shown in Table 1. The test results show that the system parameters meet the requirements. Due to the existence of various electromagnetic interferences at the system work site, corresponding anti-interference measures need to be taken at each node, such as the system power supply to take corresponding anti-interference measures. As a new emerging monitoring technology in recent years, wireless sensor networks have been widely used in industrial automatic process control. The automotive air-conditioning control system based on ZigBee wireless sensor designed in this paper has the characteristics of low cost, reliable operation, strong real-time performance, and less wiring. System energy consumption has a certain significance. The air-conditioning control system based on ZigBee has good application prospects in automotive air-conditioning systems due to its low cost, good real-time performance and strong embedding.
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In the system design, the system network structure is a star topology structure, the system's main control node is the network controller, and the other nodes are all slave nodes. The network topology structure is shown in Figure 2. The main node is set to a full-function node (FFD), responsible for system management and control; the sensor and control node is set to a simplified function node (RFD), responsible for environmental parameter data collection and air-conditioning system control. 
The temperature and humidity detection uses the digital temperature / humidity sensor SHT75 [6] (U6). The sensor has the characteristics of small size, simple and reliable, low price, digital output, no debugging, no calibration and strong interchangeability. It integrates A / D The converter and memory can automatically calibrate the relative humidity during the measurement process. U6's DATA and SCK pins are connected to U5's P0_0 and P0_1 pins respectively. U5's P0_1 controls U6's SCK pin and decides to read temperature or humidity data from U6's memory, and then stores the temperature / humidity parameters CC2430 designated storage unit. The illuminance detection uses an illuminance measurement circuit composed of photodiodes, and the photosensitive element D1 is input to P0_3 of U5 through the U4 amplifier for A / D conversion. 
The main control node circuit of the system is shown in Figure 5. The circuit is mainly composed of the main node processor, control buttons and parameter display circuit. 
