1K Temperature Probe and Node MCU

Using Arduino Sensors
1

I am trying to set up a Node MCU ESP-12E to a Thermistor probe I got on Amazon here
Bit Boss Replacement

It is reading as 1K olm resistance(I tried 2 of them) which I find odd as every example I find is for 10K resistance, but I am trying to use the following code use 1000K instead of 10000K but all the readings are way off. I know I am missing something, but can't seem to figure it out.

const double VCC = 3.3;             // NodeMCU on board 3.3v vcc
const double R2 = 1000;            // 1k ohm series resistor
const double adc_resolution = 1023; // 10-bit adc

const double A = 0.001129148;   // thermistor equation parameters
const double B = 0.000234125;
const double C = 0.0000000876741; 

void setup() {
  Serial.begin(9600);  /* Define baud rate for serial communication */
}

void loop() {
  double Vout, Rth, temperature, adc_value; 

  adc_value = analogRead(A0);
  Vout = (adc_value * VCC) / adc_resolution;
  Rth = (VCC * R2 / Vout) - R2;

/*  Steinhart-Hart Thermistor Equation:
 *  Temperature in Kelvin = 1 / (A + B[ln(R)] + C[ln(R)]^3)
 *  where A = 0.001129148, B = 0.000234125 and C = 8.76741*10^-8  */
  temperature = (1 / (A + (B * log(Rth)) + (C * pow((log(Rth)),3))));   // Temperature in kelvin

  temperature = temperature - 273.15;  // Temperature in degree celsius

  Serial.print("Rth Value = ");
  Serial.print(Rth);
  
  Serial.print("   Temperature = ");
  Serial.print(temperature);
  Serial.print(" degree celsius  ");

  Serial.print((temperature * 1.8) + 32);
  Serial.print("F");
  
  delay(500);
}

I have a 3.5mm female jack on the breadboard so it is easier to connect everything.

It is set up like this:

v+
|
thermistor
|
analog pin
|
1K resistor
|
GND

levels
levels1013Ă—418 29.6 KB

Any help would be appreciated

2

With a 1K thermistor, a 1K voltage divider resistor works best at around room temperature.

To get accurate results, the A, B and C constants used in the thermistor equation have to be matched to the thermistor itself.

You can do that by measuring the thermistor resistance at several known temperatures, and put them into this web page calculator: SRS Thermistor Calculator

Note that your program code states 1K series resistor, but your post claims that the circuit uses a 10K resistor.

1 Like
3

I suggest you start from the beginning and draw a schematic and label it as you go. You have a lot of mistooks and potentially have destroyed your micro. Show the voltages at each node. Generally the thermistor resistance is matched with the series resistor forming a 1/2 bridge. If you do not know the voltages get a multimeter and check them. A cheap one (less then $5 us will work).

4

Your diagram shows 10K for R2 but you use 1K in your program
Those A, B, C coefficients are probably not correct
The Steinhart–Hart equation uses ln not log

But MOST OF ALL, it's NOT a thermistor, It's an RTD

5

Jim-p im not sure what your mean by not a thermistor, but being mean really isnt very helpful

6

I wanted to make sure you knew it was not a thermistor.
It's an RTD not a thermistor.
You will need one of these

7

Thank you. I will try to redo the coefficients. I had done them a while ago and it made it worse so i started over. Ill do that and try again report back. I updated the schematic as well it was a misstype

8

You can change the coefficients all you want but it's still not a thermistor.

9

Ok sorry i misunderstood. I'm missing something though. I want this to be a meat sensor using the link i added to what i bought. How does the RTD connect to that? Sorry complete nubie

10

See post #6

11

What does your Ohm meter read with the probe in ice water?
In boiling water?

12

Please do not modify the original post, it makes the thread difficult or impossible to follow.

13

Ok sorry

14

Feeling cranky today?

Good luck convincing all the people who regularly use the term thermistor, including those who created the handy and popular web page entitled "SRS Thermistor Calculator" linked above.

The "Pit Boss Meat Probe" ad claims

This temperature probe uses precision high-temperature thermistors

15

Your topic has been moved. Please do not post in "Uncategorized"; see the sticky topics in Uncategorized - Arduino Forum.

16

I guess what I'm confused about is there are quite a few posts out there using this method without the RTD but have a 10k or 100k probe. I would have thought this would have been easier but adjusting that r2 variable, but now he is saying another part. What makes the most sense?

17

See the link in post #6 it explains everything

18

According to the ad, the Pit Boss replacement probe is NOT a platinum RTD, and the Adafruit tutorial for the platinum RTD amplifier is completely irrelevant to this thread.

19

Im sorry guys, but arguing over RTD verse a probe really doesnt help and is confusing me more as someone that is obviously lost.. yup I'm humble enoughto admit that. @jremington, is this issue more about the coefficients or this RTD? In simple terms.

20

Please use your multimeter to measure the resistance of the Pit Boss replacement probe at several different temperatures (say, ice water @ 0 degrees C, room temp and boiling water @ 100 degrees C) and report those in your next post.

That will help to decide what type of probe it actually is, and also allow estimating the coefficients needed to calculate temperature from resistance.