Using K-Type Thermocouple with Arduino Nano 33 BLE

[jill1335]

Hello!

I am currently working on a project where I am trying to connect a K-Type thermocouple with an Arduino Nano 33 BLE. The current code I am using is pasted below. I have verified that the amplifier and board have been correctly soldered, and I have tried re-screwing in the thermocouple multiple times, tested every connection with a multimeter for faults, and tried a new BLE board, and tried a new thermocouple. For some reason, the code right now only outputs zero, as shown below:

<
Cold Junction Temp: 0.0
Thermocouple Temp: 0.0

I have attached pictures of the circuit. I am trying to figure out what might be going wrong here, as I have tried almost everything. Any advice would be greatly, greatly appreciated.

Thanks so much!

Code:

<#include <Adafruit_MAX31856.h>

// Use software SPI: CS, DI, DO, CLK
Adafruit_MAX31856 maxthermo = Adafruit_MAX31856(13, 14, 15, 16);
// use hardware SPI, just pass in the CS pin
//Adafruit_MAX31856 maxthermo = Adafruit_MAX31856(10);

void setup() {
Serial.begin(115200);
Serial.println("MAX31856 thermocouple test");

maxthermo.begin();

maxthermo.setThermocoupleType(MAX31856_TCTYPE_K);

Serial.print("Thermocouple type: ");
switch (maxthermo.getThermocoupleType() ) {
case MAX31856_TCTYPE_B: Serial.println("B Type"); break;
case MAX31856_TCTYPE_E: Serial.println("E Type"); break;
case MAX31856_TCTYPE_J: Serial.println("J Type"); break;
case MAX31856_TCTYPE_K: Serial.println("K Type"); break;
case MAX31856_TCTYPE_N: Serial.println("N Type"); break;
case MAX31856_TCTYPE_R: Serial.println("R Type"); break;
case MAX31856_TCTYPE_S: Serial.println("S Type"); break;
case MAX31856_TCTYPE_T: Serial.println("T Type"); break;
case MAX31856_VMODE_G8: Serial.println("Voltage x8 Gain mode"); break;
case MAX31856_VMODE_G32: Serial.println("Voltage x8 Gain mode"); break;
default: Serial.println("Unknown"); break;
}

}

void loop() {
Serial.print("Cold Junction Temp: ");
Serial.println(maxthermo.readCJTemperature());

Serial.print("Thermocouple Temp: ");
Serial.println(maxthermo.readThermocoupleTemperature());
// Check and print any faults
uint8_t fault = maxthermo.readFault();
if (fault) {
if (fault & MAX31856_FAULT_CJRANGE) Serial.println("Cold Junction Range Fault");
if (fault & MAX31856_FAULT_TCRANGE) Serial.println("Thermocouple Range Fault");
if (fault & MAX31856_FAULT_CJHIGH) Serial.println("Cold Junction High Fault");
if (fault & MAX31856_FAULT_CJLOW) Serial.println("Cold Junction Low Fault");
if (fault & MAX31856_FAULT_TCHIGH) Serial.println("Thermocouple High Fault");
if (fault & MAX31856_FAULT_TCLOW) Serial.println("Thermocouple Low Fault");
if (fault & MAX31856_FAULT_OVUV) Serial.println("Over/Under Voltage Fault");
if (fault & MAX31856_FAULT_OPEN) Serial.println("Thermocouple Open Fault");
}
delay(1000);
}>

[Paul_KD7HB]

I would have to go out to the shop to look in the thermocouple drawer to be sure. I think thermocouples have a red lead and a yellow lead. Have you tried reversing them?
Paul

[Ron_Blain]

In addition to what Paul has already posted you may want to look at your thermocouple board output. The board amplifier works as follows:

Temperature = (Vout - 1.25) / 0.005 V. So for example, if the voltage is 1.5VDC, the temperature is (1.5 - 1.25) / 0.005 = 50°C

Also if not labeled on the board TC Red is Neg and Yellow is Pos or in the case of bare wire or no color code with Type K TC wire the magnetic wire is the negative lead.

Anyway I would measure the board output using a DMM and see what you get and if you heat and cool the TC the value changes.

Ron