Design of Intelligent Temperature Detection System Based on DSP

1 Intelligent temperature detection system

Intelligent temperature detection system plays an important role in smart agriculture and becomes an indispensable part of information collection in smart agriculture. Accurately obtaining temperature parameters in agricultural production or agricultural product management will help improve my country's agricultural management level and agricultural production efficiency, promote modern and precise management of agriculture, and accelerate the arrival of the era of smart agriculture.

1.1 System implementation overall solution

This intelligent temperature detection system is mainly composed of DSP main control unit, CPLD decoding unit, keyboard scanning unit, temperature detection unit, buzzer/LED alarm unit, GSM unit, and LCD display unit. When the temperature detected by the system is higher or lower than the set threshold, the system can alarm through the on-site buzzer or send the information remotely through the smart phone module. The temperature threshold and the mobile terminal number sent by the system can be set or modified through the keyboard scanning unit, and the LCD screen displays the operation process.

The system block diagram is shown in Figure 1.

1.2 DSP main control unit

This intelligent temperature detection system uses the TMS320C54x DSP chip as the main processor. TMS320C54x is a 16-bit fixed-point DSP processor produced by TI. It uses an enhanced Harvard structure with separate program bus and data bus. The storage space includes data storage space, program storage space, and I/O space. It has a dedicated hardware multiplier, uses pipeline operation, and provides special digital signal processing instructions. TMS320C54x uses a dual-voltage power supply mode with separate core voltage and peripheral voltage. It has a rich peripheral interface, a built-in watchdog timer, and provides a variety of program solidification methods. The choice of the main processor provides a guarantee for the system's low power consumption, function expansion, and product upgrades.

1.3 CPLD decoding unit

CPLD (Complex Programmable Logic Device) is a complex programmable logic device, which is a digital integrated circuit with logic functions constructed by users according to their own design requirements. Its basic design method is to use the integrated development software platform, use schematic diagrams, hardware description languages ​​and other methods to generate corresponding target files, and transfer the code to the target chip through a download cable ("in-system" programming) to realize the designed digital system. In this design, the XC95144XL-T0100 chip of XILINX is selected to complete the system hardware resource allocation, logic decoding, keyboard scanning and other tasks, and the decoding is realized by using the mixed mode of schematic diagrams and VHDL hardware programming language, and the compilation environment is Xilinx ISE 10.1 version software.

1.4 Smartphone Unit

The smart phone unit (GSM) uses Qisda's M33G module, which has an open 44-pin interface, which is convenient for users to carry out secondary development. M33G is a serial communication module. When designing the system hardware, the 16C450 chip is selected to realize the conversion from parallel port to serial port, so that the DSP processor can communicate with M33G quickly and efficiently. When designing the hardware, it is necessary to consider the fixing method of the M33G module antenna and the SIM card holder. This unit can realize the remote intelligent SMS alarm function. The connection between this unit and the system is shown in Figure 2. (Note: The +5 V, +3.3 V, and GND of each functional unit in the system are connected to the +5 V, +3.3 V, and GND of the system, which are not reflected in the figure, the same below.)

1.5 Keyboard Scanning Unit

The keyboard scanning unit is implemented by CPLD hardware description language VHDL programming, using a 4x4 keyboard, and self-defined key values. The scan input end requires four signal lines, and the scan output end requires four signal lines. The eight signal lines are connected to the I/O pins on the CPLD chip. The keyboard function is realized through CPLD software decoding. This design saves hardware resources and further improves the cost performance of the system. This unit can be used to realize the input, change, and deletion of remote mobile phone numbers. The connection between this unit and the system is shown in Figure 3.

1.6 LCD display unit

The LCD display unit uses AM-17622 LCD screen. AM-17622 is a 2.0-inch TFT-LCD screen produced by Taiwan Jingcai Optoelectronics Technology Co., Ltd. It has a white LED backlight and a driver chip HX8309. It supports 8/9/16/18-bit parallel interface design and has rich command functions. This system uses a 16-bit parallel interface design, and the connection with the system is shown in Figure 4. The LCD screen can display the monitored temperature value in real time. When the mobile phone number is entered, changed, or deleted, the LCD screen displays the current operation content.

1.7 Buzzer/LED light unit

The buzzer/LED light unit is responsible for the system alarm in this system. When the deviation between the system temperature and the set temperature is not within the set control range, the buzzer/LED light alarms. In the design, the XF and HD2 pins of TMS320C54x are used to control the operation of the buzzer and LED light through the current amplifier circuit respectively.

2 Temperature Detection Unit Hardware Design

The temperature sensor uses the DS18B20 chip with a high cost performance ratio. This chip is a single bus device produced by DALLAs, which can directly read the temperature value of the object being measured, and the applicable voltage range is 3 to 5 V. DS18B20 has strong anti-interference ability, high conversion accuracy, simple interface circuit, and can realize multi-point network temperature measurement, which brings great convenience to hardware design work.

2.1 DS18B20 Features

DS18B20 provides 9-12-bit precision temperature measurement, and the temperature measurement range is -55 to +125°C. In the range of -10 to 85°C, the measurement resolution is ±0.5°C, the minimum increment value can be 0.0625°C, and the power supply range is 3.0 to 5.5 V. It takes up to 750 ms to convert the measured temperature into a 12-bit digital quantity. DS18B20 has two power supply modes: external power supply and parasitic power supply. It uses signal line parasitic power supply and does not require additional external power supply. It is particularly useful in situations where remote temperature detection is required and space is limited. Each DS18B20 has a unique 64-bit serial number, which allows multiple DS18B20s to work on a single bus at the same time. 2.2 Hardware Circuit

The hardware interface connection between DS18B20 and TMS320C54x DSP processor is extremely simple. In the design, DS18820 is powered by an external 3.3 V power supply, which is consistent with the peripheral power supply voltage of TMS320C54x DSP processor; the key signal line of DS18B20 is connected to a GPIO port of TMS320C54x DSP, and the bidirectional input and output characteristics of GPIO port are used to complete the read and write functions of DS18B20 chip. The data pin HD1 of TMS320C54x DSP peripheral HPI host interface unit is selected to connect with it, and the HD1 pin is configured as a general input and output function to realize the timely temperature collection of DS18B20 chip: DQ signal line needs to add a 4.7 KΩ pull-up resistor to ensure the driving ability of HD1 data line. The GND end of DS18B20 can be connected to the GND of the system.

3 Temperature detection software implementation

The overall implementation process of the DSP-based intelligent temperature detection system is shown in Figure 6.

The DS18B20 chip has very high requirements for timing and electrical parameters. When writing software programs, its working timing must be strictly followed. If any link is wrong, the DS18B20 will not work properly. This system uses a DS18B20 chip, and the serial number reading can be ignored when writing software programs. When temperature node control is added to the hardware, it is necessary to collect temperature from multiple DS18B20s. The DS18B20 serial number can be read and matched with ROM instructions to access each sensor in sequence to achieve temperature collection for each sensor. When the DS18B20 chip is reset, if the chip reset is unsuccessful, the DS18B20 will not generate a response signal. A digital oscilloscope should be used to track and check whether its working timing is correct. The process of the temperature detection unit software implementation is shown in Figure 7.

4 Conclusion

The DSP-based intelligent temperature detection system has been verified by experiments to be able to detect the temperature value of the current environment in real time. The measurement results have small errors and high precision, and the measurement results can be displayed in real time on the display screen. When the system detects that the current temperature is greater than or less than the set temperature threshold range, the system will alarm through the on-site buzzer/LED light or through a remote intelligent SMS. The system can realize temperature measurement by networking multiple temperature nodes, eliminating the ZigBee networking communication technology, improving the cost-effectiveness of the system, and laying a certain technical foundation for the realization of intelligent management in agriculture. The intelligent temperature detection system has good economy and practicality.