SunFounder Thales Kit, Руководство пользователя

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SunFounder Thales Kit for Raspberry Pi Pico, Release 1.0
(continued from previous page)
thermistor = machine . ADC( 28 )
while True :
temperature_value = thermistor . read_u16()
Vr = 3.3
*
float (temperature_value) / 65535
Rt = 10000
*
Vr / ( 3.3 - Vr)
temp = 1 / (((math . log(Rt / 10000 )) / 3950 ) + ( 1 / ( 273.15 + 25 )))
Cel = temp - 273.15
Fah = Cel
*
1.8 + 32
print ( 'Celsius: %.2f C Fahrenheit: %.2f F' % (Cel, Fah))
utime . sleep_ms( 200 )
How it works?
Each thermistor has a normal resistance. Here it is 10k ohm, which is measured under 25 degree Celsius. When
the temperature gets higher, the resistance of the thermistor decreases. Then the voltage data is converted to digital
quantities by the A/D adapter.
The temperature in Celsius or Fahrenheit is output via programming.
import math
There is a numerics library which declares a set of functions to compute common mathematical operations and trans-
formations.
• math
temperature_value = thermistor . read_u16()
This function is used to read the value of the thermistor.
Vr = 3.3
*
float (temperature_value) / 65535
Rt = 10000
*
Vr / ( 3.3 - Vr)
temp = 1 / (((math . log(Rt / 10000 )) / 3950 ) + ( 1 / ( 273.15 + 25 )))
Cel = temp - 273.15
Fah = Cel
*
1.8 + 32
print ( 'Celsius: %.2f C Fahrenheit: %.2f F' % (Cel, Fah))
utime . sleep_ms( 200 )
These calculations convert the thermistor values into centigrade degree and Fahrenheit degree.
Vr = 3.3
*
float (temperature_value) / 65535
Rt = 10000
*
Vr / ( 3.3 - Vr)
In the two lines of code above, the voltage is first calculated using the read analoge value, and then get Rt (the resistance
of the thermistor).
temp = 1 / (((math . log(Rt / 10000 )) / 3950 ) + ( 1 / ( 273.15 + 25 )))
Note:
Here is the relation between the resistance and temperature:
RT =RN expB(1/TK – 1/TN)
• RT is the resistance of the NTC thermistor when the temperature is TK.
92 Chapter 3. For MicroPython User