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A thermistor is a type of resistor whose resistance is dependent on temperature. Thermistors are widely used as temperature sensors namely positive temperature coefficient (PTC ) and negative temperature coefficient (NTC) in accordance with the temperature coefficient. With PTC, resistance increases with the increase of temperature. While with NTC, resistance decreases with the increase of temperature. We are using a NTC thermistor whose resistance decreases with the increase of temperature. Convert the voltage of CH0 into digital value via the ADC. And then convert the resistance of the thermistor into centigrade temperature or Fahrenheit degree through program processing. Specific process: 1. Read the analog value of CH0 in the following circuit and calculate the voltage of CH0 based on the property of ADC (refers to the voltage reference (Vref), which is 5V and the analog reference (Aref), which is 10 bit ADC for Arduino namely Aref=1023 and 8 bit ADC for ADC0832 namely Aref=255 )and the serial resistanceοΌcalculate the Voltage Vr of CH0: 2. Calculate the value of Rt through the geometric relationship between voltage and resistance. 3. Calculate the value of Kelvin temperature (Tk) of the thermistor based on the negative temperature coefficient formula of resistance (the governing equation is Arrhenius equation), which describes that an insulator’s resistance varies with temperature. 4. Then convert Tk into centigrade temperature or Fahrenheit degree The following is the specific process: 1. Build the circuit and read the analog value. If you are using a Raspberry board, you need to use an ADC chip to read the analog value since it is not capable of doing so. Here we take the ADC0832 for example. For Arduino, you can use the ADC chip inside it. Connect CH0 to any pin from pin A0 to pin A5 to read the value. Here the ππππ of Arduino board and ADC0832 are both 5V. ADC0832: π΄πππ = 255οΌ Arduino: π΄πππ = 1023. Here we regard the analog value as AT.The ratio of π΄ π and π΄πππ equals to that of ππ and ππππ ( the property of ADC). That is : π΄π ππ = π΄πππ ππππ Then ππ = π΄ π β ππππ π΄πππ ππππ and π΄πππ are the constants. Then the value of ππ can be calculated. 2. Calculate the value of Rt according to the following equation: ππ ππ = π π + π 1 π 1 ππ refers to the power supply voltage at the left, which is 5V. π 1 refers to the 10k resistor. Therefore, the value of RT can be calculated: π π = ππ β π 1 − π 1 ππ That is : π π = 5π£ × 10 000πΊ − 10 000πΊ ππ 3. Calculate the Kelvin temperature (Tk) based on π π : π΅ π π = π΄ β β― ππ A and B are the constants. Beta (B) is NTC. For the thermistor we are using, π΅ = 3950. Here π = 2.71828 … We use a 10k Ohm thermistor. When T0=25, π 0 = 10 000πΊ A= π π π΅ π ππ ∴ π 0 π΅ β― π0 = π π π΅ π ππ Then the value of ππ can be calculated through the given parameters οΌπ 0 οΌπ΅οΌ β―οΌπ0 οΌ π π οΌ Continue to change the equation: π π = π 0 β β― β― (− π΅ π΅ (− + ) π0 ππ π΅ π΅ (− + ) π0 ππ = π π π 0 π΅ π΅ π π + ) = ln ( ) π0 ππ π 0 π΅ π π π΅ = ln ( ) + ππ π 0 π0 π΅ ππ = π π΅ ln ( π π ) + π 0 0 Then the value of ππ has been calculated. 4. Convert ππ into centigrade temperature or Fahrenheit degree we are familiar with. Centigrade Temperature (ππΆ ) ππΆ = ππ − 273.15 εζ°εΊ¦οΌ Fahrenheit Degree (ππΉ ) ππΉ = (ππ − 273.15) × 1.8000 + 32.00 The above-mentioned process can be simplified as: 1. Read the value of π΄ π and calculate the value of ππ οΌππ = 2. Calculate the value ofπ π οΌπ π = 3. Calculate the value of ππ οΌππ = ππ ×π 1 ππ π΄π ×ππππ π΄πππ − π 1 π΅ π π΅ ln( π )+ π 0 π0 4. Calculate the value of ππΆ /ππΉ οΌ ππΆ = ππ − 273.15 ππΉ = (ππ − 273.15) × 1.8000 + 32.00 Now, we have learned how to convert the resistance of a thermistor into centigrade temperature or Fahrenheit degree. For more information, you can also refer to this link. https://en.wikipedia.org/wiki/Thermistor