Nano RP2040 temperature value not changing

Official Hardware Nano Family Nano RP2040 Connect
1

Hi,

I have a Arduino Nano RP2040 Connect utlising a 10K thermistor & 10K resistor. Its input is on A0. The MicroPython code I'm using continously displays 24C (varying only +/- 0.02C) in Thonny's serial monitor. It does this even when I completely disconnect the thermistor.
(As a test, I'm able to get good temperature readings with an Arduino sketch on an identical ciruit on another Nano RP2040.)

My programmer is conversant in Python, but new to MicroPython, and microcontrollers.
We're a bit baffled. Any suggestions of what's wrong?

TIA

The code is:

from machine import ADC, Pin
import math
import time

adc = ADC(Pin(26))  # create ADC object on ADC pin

RT0 = 10000
B = 3950
VCC = 3.3
R = 10000
T0 = 25 + 273.15


while True:
    # read value, 0-65535 across voltage range 0.0v - 3.3v. equivalent to - VRT = analogRead(A0)
    VRT = adc.read_u16()
    VRT = (3.3 / 1023.00) * VRT  # Conversion to voltage
    VR = VCC - VRT
    RT = VRT / (VR / R) * -1
    ln = math.log(RT / RT0)
    TX = (1 / ((ln / B) + (1 / T0)))  # Temperature from thermistor
    TX = TX - 273.15  # Conversion to Celsius
    print("Temperature: ", TX)    
    time.sleep_ms(500)  # sleep for 500 milliseconds

Circuit:

image
image795×537 80.5 KB

Correction to circuit - its a 1/4 watt resistor. Not 1.4 watt.

2

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