A design of remote intelligent automobile temperature control system based on GSM

The system uses the GSM remote communication system to control the operation of the air conditioner and other equipment in the car. Users can achieve human-computer interaction through text messages, overcoming the problem of short distance of infrared, wireless and other remote control, and can also monitor the status of the car in real time, providing convenience for car owners.

1 System Principle and Structure

1.1 System Function Introduction

The system can automatically collect the ambient temperature and light intensity of the scene at a speed of 10 times/s, collect the opening and closing status of the air conditioner and curtains, and display them in real time on the LCD screen. The temperature sensing range is -55～+125℃, with an accuracy of ±0.5℃. The light intensity range is divided into 5 levels: strong, relatively strong, medium, relatively weak, and weak. The status of the air conditioner and curtains is open or closed.

Users can use mobile phones or PHS terminals to communicate with the system connected to the GSM module. The communication range is the entire range covered by the mobile network, achieving a truly infinite communication range. Specific communications are:

1) When the system detects that the temperature and light intensity exceed the set standard values, it will automatically send a Chinese reminder text message to the user's mobile phone.

2) Users can send Chinese text messages to the system to check the temperature, light intensity, air conditioning and curtains in the car in real time.

3) The user can send control signals to control three actions in the car: ① Close and open the curtains. The MCU gives a high level to LG9110 to drive the motor, and the motor rotates forward and reverse to achieve the action of closing and opening the curtains. ② Start and stop the air conditioner. The MCU gives a high level to LG9110 to drive the fan blades on the DC motor to simulate the start and stop of the car air conditioner. ③ Start and stop the engine. The engine is simulated by an electric motor, and the MCU controls its rotation and stop to simulate the start and stop of the car engine.

1.2 System Solution

The hardware circuit of this design consists of seven parts: power module, control module, temperature module, light intensity module, display module, motor drive module and GSM communication module. The relationship between each module is shown in Figure 1.

1.2.1 Main control system module

The main control system module adopts the STC89C516RD+ microcontroller based on the 51 core produced by Hongjing Technology to complete signal acquisition, control and communication functions. It has 64K on-chip FLASHROM and 1280B on-chip RAM resources, and has a 51 core, strong encryption, and the ISP download method is simple and easy to use. It has a large storage capacity and is very suitable for development and design.

In this design, the STC89C516RD+ microcontroller serves as the control core. It first collects data from various external sensors through the forward channel, then analyzes and compares it with the internal reference data through different adaptive algorithms of each input module, and then sends warning text messages to car users through the GSM/CDMA network. Car users can also send various query and control information to the system through the GSM/CDMA network.

1.2.2 Temperature module

The temperature module uses the DS18B20 one-line digital temperature sensor produced by DALLAS, USA. The DS1820 digital thermometer provides a 9-bit (binary) temperature reading to indicate the temperature information of the device, which is sent to the host CPU through a single-line interface. The measured temperature value is -55 to +125°C. The interface circuit between the temperature module and the main control CPU is shown in Figure 2.

1.2.3 Light intensity module

The light intensity module converts the analog signal generated by the photoresistor sensing the light intensity into a digital signal through ADC0832 and samples it to the microcontroller to collect the light intensity data inside the car.

1.2.4 LCD display module

The display module uses the LM6029 LCD display with Chinese character library for display output. The LM6029 dot matrix graphic LCD display module uses the S680724 controller, with a dot matrix of 128x64, a built-in Chinese character library, and an 8-bit parallel interface to connect to the main control CPU. The interface circuit between the display module and the main control CPU is shown in Figure 3.

1.2.5 Motor drive module

The DC motor is driven by the LG9110 driver chip, which can drive the DC motor in forward and reverse rotation through the control line, thereby controlling the action of the external output device. The interface circuit between the motor drive module and the main control CPU is shown in Figure 4.

1.2.6GSM module

The GSM module uses TC35 produced by Siemens, which has the function of sending and receiving Chinese and English text messages. TC35 is a new generation of wireless communication GSM module launched by Siemens. It has its own RS232 communication interface, which can be easily connected to PC and single-chip computer for communication. It can quickly, safely and reliably realize the data, voice transmission, short message service (Short Message Service) and fax in the system solution. The working voltage of TC35 module is 3.3~5.5V, and it can work in the two frequency bands of 900MHz and 1800MHz. The power consumption of the frequency bands is 2W (900M) and 1W (1800M) respectively.

TC35 uses RS232 level interface and can be directly connected to PC. In this design, a TTL to RS232 level circuit is required between the UART of the main control CPU and TC35.

1.2.7 Power Module

The power module uses the LM2576DC/DC step-down switching power supply, which can reduce the +12V cigarette lighter DC voltage to multiple DC voltages such as +5V and +3.3V to supply power to other modules.

1.3 Software Process

The system software is divided into four parts. The first part is the DS18B20 temperature sensor, which needs to set the correct timing to read and output information; the second part is the light sensor, which uses ADC0832 to convert the analog voltage value sensed by the photoresistor into a digital signal and transmit it to the microcontroller; the third part is the LM6029 display screen, which is controlled by the microcontroller to display the status of the car; these three parts constitute the main program. The fourth part is the GSM module, and the microcontroller receives and sends the information of the GSM module communication through the serial port interrupt. The system flow chart is shown in Figure 5.

2 System Testing

2.1 Test plan

The system test adopts the method of debugging and testing each module. First, use a multimeter to test whether the output of the power module is 3.3V and 5V designed by the system; then download and test the minimum system of the microcontroller through ISP; then connect the LCD module to test whether it can display normally; then connect the light intensity sensor and temperature sensor to test whether the temperature and light intensity are proportional to the collected value; then test whether the curtain, air conditioner, and engine simulation system can work normally when the power module is working normally; finally, use the serial port of the PC to debug the serial communication between the GSM module.

Connect the whole system, connect the power module to the power supply, repeat the above steps, send information to the GSM module through the mobile phone, send query instructions, and observe whether the information data received by the mobile phone and the data displayed on the LCD screen are consistent with the data displayed. Send control instructions to observe whether the system rotates the simulated engine and air conditioner according to the user's requirements, and whether the curtains are automatically pulled up and closed. Through the above tests, you can judge whether the whole machine is running normally.

2.2 Test Data

The test data consists of the following 4 parts:

1) The output of the power module is normal when tested by a multimeter. The error between +5V and +3.3V is within ±0.1V. After connecting all loads, the output current reaches +2A.

2) By setting different standard status values, it is tested that the system automatically sends SMS messages to the terminal when the value exceeds the standard.

3) Send query commands to the system through the terminal, and test that the information data received by the mobile phone is completely consistent with the data displayed on the LCD screen;

4) Send control information to the system through the terminal, and test that the actions of the air conditioner and curtains controlled by the motor are the same as the instructions.

2.3 Results Analysis

After various performance tests, the system's indicators and parameters have basically achieved the expected results. If the interfaces of the air conditioner and engine on the actual car can be taken into consideration, the system will be more perfect and worthy of large-scale promotion.

3 Conclusion

The features of this project are as follows:

1) The system can automatically transmit the excessive information in the car to the user terminal through the GSM network, and can also be queried and controlled remotely by the user outside the car, overcoming the operational inconvenience caused by the distance between the user and the car;

2) The system can automatically collect various parameters in the vehicle, automatically compare them with the standard parameters set by the user, automatically notify the user when they exceed the standard, automatically identify the query information and control information sent back by the user, send real-time status based on the query information sent back, and automatically convert the control information sent back into control instructions. The entire system has the characteristics of artificial intelligence.