NTC sensor – RPI Pico

Table of Contents

NTC Readout (micropython)
MicroPython Code Example
Micropython code using ADS1115 and NTC 50K 3950
Products
Sources

NTC Readout (micropython) #

We wire the circuit on the Breadboard and connect it to the Raspberry Pi Pico device.

In the MicroPython code we need to do the following steps:

We measure Vout using the ADC on Raspberry Pi Pico
We calculate Rt using the Voltagee Divider Equation
Then we use Steinhart-Hart equation for finding the Temperature
Finally we convert from degrees Kelvin to Celsius

MicroPython Code Example #

from machine import ADC
from time import sleep
import math

adcpin = 28
thermistor = ADC(adcpin)

# Voltage Divider
Vin = 3.3
Ro = 10000  # 10k Resistor

# Steinhart Constants
A = 0.001129148
B = 0.000234125
C = 0.0000000876741

while True:
    # Get Voltage value from ADC   
    adc = thermistor.read_u16() >> 4 # Get original 12-bit value 0-4096
    print ("ADC Value:", adc)
    Vout = (3.3/4096) * adc
    
    # Calculate Resistance
    Rt = (Vout * Ro) / (Vin - Vout) 
    #Rt = 10000  # Used for Testing. Setting Rt=10k should give TempC=25
    
    # Steinhart - Hart Equation
    TempK = 1 / (A + (B * math.log(Rt)) + C * math.pow(math.log(Rt), 3))

    # Convert from Kelvin to Celsius
    TempC = TempK - 273.15
    
    #Correction for %5
    TempC = TempC - 7

    print(round(TempC, 1))
    sleep(1)

Micropython code using ADS1115 and NTC 50K 3950 #

(NTC connected to channel 0 on ADS 1115 with voltage divider)

from machine import I2C, Pin
from time import sleep
from ads1x15 import ADS1115
import math

i2c=I2C(0, sda=Pin(8), scl=Pin(9))
adc = ADS1115(i2c, address=0x48, gain=0)

def calculate_temperature(adc_value):
    # ADC Parameters
    ADCvccpow = 5.0
    ADCvccmax = 6.144  # ads1115 gain 0
    ADCmaxvalue = 32768  # signed 16-bit
    # Voltage Divider
    R1 = 50000  # Pull-up resistor
    # NTC Parameters
    Rntc = 50000  # Resistance at 25°C (Ohms)
    Beta = 3950  # Beta coefficient
    Tnom = 25  # Nominal temperature in Celsius
    T0 = 273.15 + Tnom  # Convert 25°C to Kelvin
    Vout = (ADCvccmax / ADCmaxvalue) * adc_value # Get Voltage value from ADC
    #print(f"Vout: {Vout:.3f} V") # Debugging print statement
    # Prevent division by zero or negative resistance
    if Vout <= 0 or Vout >= ADCvccpow:
        return None  # Ongeldige meting
    R_ntc = R1 * (ADCvccpow / Vout - 1) # Calculate Resistance
    #print(f"R_ntc: {R_ntc:.1f} Ohm") # Debugging print statement
    # Prevent log errors
    if R_ntc <= 0:
        return None  # Ongeldige waarde
    TempK = 1 / ((1 / T0) + (-1 / Beta) * math.log(R_ntc / Rntc)) # Calculate temperature using the Steinhart-Hart equation
    TempC = TempK - 273.15 # Convert from Kelvin to Celsius
    return round(TempC, 2)

while True:
   adc_value = adc.read(0, 0)
   temperature = calculate_temperature(adc_value)
   print(f"Temperatuur: {temperature} °C")
   sleep(.5)