Design of embedded temperature control system based on ARM microprocessor

Aiming at the problem of color temperature control in shadowless lighting system, this paper designs an embedded temperature regulator based on ARM microprocessor. The whole intelligent temperature controller consists of microcontroller, digital display module, temperature sensor, PWM heating module, clock circuit and other components. The PID adjustment circuit, serial communication circuit, microcontroller peripheral communication interface, PWM heating control circuit and software module are designed, and the whole hardware and software system is built. Finally, experiments and verifications are carried out. The results show that the embedded PID temperature controller can meet the design requirements, has good adjustment accuracy, and maintains constant temperature control characteristics, and can be put into practical application.

The temperature controller is an important control device. In household appliances with sensitive performance requirements, the temperature controller is one of the necessary control systems. It has broad application prospects in large-scale industries and daily life. Many application fields require high-precision constant temperature control. For example, according to external changes, the corresponding LED brightness can be adjusted at any time to achieve the required color temperature value, which can achieve better lighting and decorative effects. Introducing PID control in the temperature controller can obtain a more ideal control effect, and the temperature fluctuation can be controlled within 0-125℃. This technology has been applied to products such as timed temperature control fermenters and health pads, and it runs well and has achieved good social and economic benefits. Therefore, how to introduce PID temperature control system in the color temperature control of shadowless lighting system has become one of the current research topics. Moreover, with the development of modern computer technology, communication technology, and digital technology, it has become a trend to introduce embedded systems in temperature control systems. It has the advantages of strong scalability, high integration, and precise control.

1 Overview of Embedded Temperature Control System

1.1 Embedded Overview

From the perspective of the composition of an embedded system, an embedded system is a computer system that integrates software and hardware and can work independently; from the appearance, an embedded system is more like a "programmable" electronic component; from a functional perspective, it is a controller that precisely controls the execution object, making it "intelligent".

Embedded systems are mainly used to complete signal control functions. They are small in size and compact in structure. They can be embedded as a component in the controlled device. They provide user interfaces, manage information input and output, monitor equipment operation, and make equipment and application products more intelligent and cost-effective. According to the definition of IEEE (Institute of Electrical and Electronics Engineers), embedded systems are devices that control, monitor or assist equipment, machines or factory operations. It can be seen that this definition is mainly considered from the application aspect. The main difference between embedded systems and general-purpose computers is that their application purposes are different. Whether in terms of hardware or software, each embedded system is "tailor-made" for different applications or for specific functions, and more factors such as space cost need to be considered.

Embedded systems are highly specialized, real-time and reliable, easy to customize, and have low power consumption. Temperature controllers based on embedded technology are easy to expand and powerful. They can not only simplify the system in terms of hardware structure, but also improve performance, thereby reducing system costs for more flexible deployment of applications. Embedded is the development direction of temperature control controllers.

1.2 PID regulation principle

The proportional, integral, and differential controller is the most widely used regulator in engineering practice, referred to as PID regulator. PID control appeared in the 1950s and became one of the main technologies of industrial control, mainly because of its simple structure, reliable operation, good stability, and easy adjustment.

2 System Design

2.1 Overall hardware design

The embedded ARM temperature regulator designed in this paper mainly consists of the following modules: display module, temperature sensor, clock circuit module, alarm module, ARM core S3C2440, PID control module, PWM heating control module, and reset circuit. The overall hardware design of the system is shown in Figure 1.

2.2 PWM heating module design

The PWM heating module is composed of a 3524 chip and some peripheral components. The rectangular wave is generated by the internal oscillator of the 3524 chip, and its frequency is:

f≈1.30/(RT-CT) (1)

The potentiometer RT is used to adjust the frequency, and the pulse width modulator is composed of the differential amplifier, comparator, oscillator, etc. inside the 3524 chip. The duty cycle of the rectangular wave output is controlled by the output voltage of the differential amplifier.

2.3 PID circuit

The purpose of designing a PID regulator is to adjust the actual value of the controlled object to correspond to the new set value, which can reduce or eliminate the influence of interference. In the field of automatic control, due to the requirements of control stability and reliability, analog PID control technology is simple and reliable, low cost, and widely used and mature. Figure 2 is a block diagram of the composition of a PID regulator.

In the control unit, the input signal Vi is subjected to PID operation through PI and PD circuits to obtain Vo.

The working principle of PID regulator is: Vi is the deviation between the signal detected and amplified by the temperature sensor and the set signal. The regulator performs proportional, integral and differential operations on the deviation, thereby outputting an appropriate control signal Vo to the next level circuit, prompting the measured value signal to return to the given value, and achieving the effect of automatic control. The three parameters (P, I, D) of the regulator are independently adjustable. In practical applications, the engineering setting method is used to determine the P, I, and D parameters. This method is directly carried out in the test of the control system, and the method is simple and easy to master, and is widely used in engineering practice.

2.4 Software Design

Software modules are very important in temperature control and regulation systems. In this paper, since there are many software systems, a modular design scheme is adopted, that is, the entire software is composed of many independent small software modules, which are connected and communicated through specific software interfaces to form a modular structure according to their functions. Its main workflow is shown in Figure 3.

First, the controller parameters are initialized, and then the temperature set value is read. If it is successfully obtained, the PWM heating module is controlled to execute; the temperature sensor module obtains the actual temperature and compares it with the set value. If they are the same, the process ends; if they are different, the heating module is adjusted through PID control until they are the same.

3 Experiments and Verification

According to the overall hardware design block diagram 1, connect the functional blocks, download the software to the ARM system, connect the temperature sensor DS18B20 to the ARM controller through the serial interface, and build an experimental environment for experimental verification. When the set temperature is 50 ℃, the running results are shown in Figure 4.

When the set temperature is 90 ℃, the operation results are shown in Figure 5.

4 Conclusion

This paper designs an ARM-based PID temperature controller, uses DS18B20 as the temperature sensor, communicates with the microprocessor via a serial port, the microprocessor uses ARM S3C2440, and the heating module uses PWM. The overall hardware circuit and software workflow are given, and finally experiments and verifications are carried out. The results show that the controller has high adjustment accuracy and can be used in industrial sites.