Overview:
In this paper, a temperature measurement system for solar water heater based on HT48R54A single chip microcomputer is designed. The system uses a negative temperature coefficient thermistor as the temperature sensing element, and realizes the temperature collection through the RC charge and discharge type temperature measuring circuit. According to the relationship between the thermistor temperature and the resistance value, the temperature table is established, and the current table is detected by the table lookup method. temperature. The system is simple in structure, low in price, and occupies very little system resources.
0 Introduction With the continuous improvement of people's living standards and environmental awareness, more and more consumers tend to choose solar water heaters. Solar water heaters with auxiliary electric heating function are especially favored by the market. Solar water heaters with auxiliary electric heating function can Automatic heating according to the temperature set by the user, the first prerequisite to complete this function is to accurately measure the water temperature of the water heater. At present, the methods for measuring the water temperature include: using the temperature sensor DS18B20, using a thermistor and converting the resistance value into a frequency by a voltage frequency conversion circuit, etc. The temperature sensor DS18B20 is used to measure the water temperature, and the interface circuit is simple, but the price is relatively expensive. The thermistor is used and the water temperature is measured by a voltage-frequency conversion circuit, which increases the system cost due to the introduction of the voltage-frequency conversion circuit. In this paper, the author proposes a simple and inexpensive method for measuring temperature using a thermistor, and occupies very few microcontroller I/O interfaces. This method can also be applied to other temperature measurement systems.
1 Solar water heater temperature measurement circuit and principle Solar water heater temperature measurement circuit shown in Figure 1, the thermistor in Figure 1 is a negative temperature coefficient thermistor (10 kΩ / 25 ° C), that is, as the temperature increases, The resistance value is reduced. By identifying the size of the resistor, the purpose of detecting the temperature is achieved. PA0, PA4 and PA5 are the I/O ports of the HT48R54A microcontroller. PA0, PA4 and PA5 can set their input/output status in real time through software instructions according to actual needs. 
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