1. Program design, comparison and argumentation
1.1 Sensor selection
Solution 1: In order to achieve the function of tracking the heat source, the temperature sensor DS18B20 is used for real-time temperature acquisition. The value of the internal register is read by the 51 MCU, and the read temperature is compared with the set temperature. Exceeding the microcontroller will perform related actions. This solution has the advantage of simple hardware circuit, but the cost is high, and the programming is complicated. The extreme temperature of the DS18B20 is 125 degrees, which is very easy to burn out and cannot realize related functions.
Solution 2: The thermistor and the AD conversion chip are used for tracking the heat source. The voltage change is caused by the change of the thermistor, and the AD chip replaces the voltage analog quantity into a digital quantity, and the digital program reads the digital quantity to execute the relevant program to control the stepping motor. Although this scheme is feasible, the electrical signal processing circuit before AD is relatively complicated and costly. So give up using the program.
Solution 3: Using the thermistor and the dual voltage comparator LM393 for the acquisition and processing of electrical signals, the SC89F516 microcontroller is used to judge the high and low levels, and the stepper motor is realized by programming the ULN2803 chip with low cost, low power consumption and large driving current. Control, thus enabling automatic search of heat sources. The solution has the advantages of low cost, low power consumption, simple structure, and convenient program writing.
After various tests and experiments, we adopted the third option as the final solution.
1.2 The choice of the main control chip
Solution 1: Adopt STC89C52 single-chip microcomputer, STC89C52 single-chip microcomputer is an 8-bit single-chip microcomputer introduced by ST company. The MCU has the advantages of simple programming and low price, and has a high-performance CMOS 8-bit microcontroller with 8K in-system programmable Flash memory. However, its memory is too small to run larger programs. This project requires encryption of the program, which cannot be implemented by the microcontroller. Therefore, it will not be used.
Solution 2: Using STM32C8T6 MCU, STM32C8T6 MCU is a relatively high-end MCU. The MCU has powerful functions and is rich in built-in. It is a 32-bit MCU with cortex M3 core, clock frequency up to 72MHz, 32 bits in the same class. The power consumption in the machine is the smallest. Due to its powerful features, its programming is relatively complicated. Moreover, the cost is relatively high, and it is difficult to implement the function of preventing the program from cracking and blocking the loophole.
Solution 3: Adopt SC89F516 single-chip microcomputer produced by Shenzhen Hualian Company. This single-chip microcomputer is a high-speed and high-efficiency 8-bit single-chip microcomputer. This single-chip microcomputer is compatible with all the advantages of the traditional 51 single-chip microcomputer. The microcontroller contains ADC and SPI modules. Is a very cost-effective microcontroller. The biggest advantage of this MCU is the function of preventing the program from cracking and blocking the vulnerability. It is also the highlight of the design of this project.
After comparison plan 3 is the best choice.
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