MAX6675 Thermocouple Temperature Module

Description

The MAX6675 Thermocouple Temperature Module is a digital converter that has a range of 0°C up to 1024°C when paired with a suitable K-Type thermocouple.

PACKAGE INCLUDES:

• MAX6675 Thermocouple Temperature Module

KEY FEATURES OF MAX6675 THERMOCOUPLE TEMPERATURE MODULE:

• Module uses MAX6675 IC which can handle readings from 0°C to 1024°C
• 0.25°C resolution, ±3°C accuracy
• Compatible with K-Type thermocouples that use spade lug connections
• Uses 3-wire SPI interface
• 3.0 – 5.5V operation

This module utilizes the MAX6675 IC which is a cold-junction-compensated K-Type thermocouple to digital converter.  The MAX6675 has a maximum measurement range of 0°C to +1024°C depending on the thermocouple it is paired with.

Thermocouples work on the principal that dissimilar metals that are welded together at a single point will create a small voltage that will vary with the temperature. The main advantage of thermocouples over typical thermal sensing electronics such as the DS18B20 is that the sensing range can go much higher since a robust metallic probe is used to sense the temperature while the electronics hang back in a safe location.  The flip side is that the reading may not be quite as accurate using a thermocouple.

Thermocouples come in many different varieties from very fine wires if you want to measure a small object, to very thick metal sheathed wires with very high temperature ranges.

The module interfaces with a microcontroller via a 3-wire SPI interface.  There are libraries available that make interfacing very easy as shown in our example below.

Module Connections

When hooking up a thermocouple, the red lead of the thermocouple typically attaches to the ‘+’ terminal on the module.  If the reading goes down when temperature increases, then the leads should be reversed.

1 x 5 Header

• GND =  Connect to system ground.  This ground needs to be in common with the MCU.
• VCC =   Connect to 3.0 – 5.5V.  Typically connected to MCU operating power.
• SCK =   Serial Clock Input.  Connect to any digital pin on MCU.
• CS =      Chip Select.  Connect to any digital pin on MCU.
• SO  =     Serial Data Output.  Connect to any digital pin on MCU.

OUR EVALUATION RESULTS:

This is a commonly used module for temperature measurement.

We measured a typical current draw of the module at 500-700uA and the MAX6675 chip max spec is 1.5mA.  A common misconception is that the module draws up to 50mA.  That spec comes from the max current the SO pin can deliver, so that high current would never be seen under normal operation.  Since the module draws very little power (<1.5ma), it can even be powered from a digital output pin on the MCU if desired.  If this approach is taken and the power is turned off to the MAX6675 between reads, the power should be allowed to stabilize for a couple of seconds once power is applied before a reading is attempted.

Also keep in mind that though the reading resolution is 0.25C, the overall accuracy is ± 3C.  This is typically fine for most applications when measuring higher temperatures as thermocouples are typically used for, but if you are trying to measure basic ambient temperature, the reading may be off by a couple of degrees.

Once the MAX6675 library is installed, using the device is fairly simple as shown in the code snippet below.  This library uses software SPI, so you do not need to connect to hardware SPI interface pins.  Just hook up 3 digital pins to use as the SPI interface (we are using pins 8,9,10 in the example) and provide power and ground.  You will also need a suitable K-Type thermocouple hooked up to the screw terminals.

This program just takes readings every second and reports the temperature in degrees Fahrenheit and Celsius to the Serial Monitor window.

MAX6675 Thermocouple Temperature Module Example Program

/*MAX 6675 Thermocouple Module Test

Basic code for reading the MAX6675 chip via SPI interface
Requires installation of 'max6675.h' library
*/
#include "max6675.h"

int const SO_PIN = 8;   // Can use any digital pins for these assignments
int const CS_PIN = 9;
int const SCK_PIN = 10;

MAX6675 ktc(SCK_PIN, CS_PIN, SO_PIN);  // Create an instance of MAX6675 control
//===============================================================================
//  Initialization
//===============================================================================
void setup() {
  Serial.begin(9600);  // Set comm speed for debug window messages
  delay(1000);        // give the MAX6675 a little time to settle
}
//===============================================================================
//  Main
//===============================================================================
void loop() {
  // Read and print the values from the module in both degrees C and F
   Serial.print("Deg C = "); 
   Serial.print(ktc.readCelsius());
   Serial.print("\t Deg F = ");
   Serial.println(ktc.readFahrenheit());
 
   delay(1000);
}

BEFORE THEY ARE SHIPPED, THESE MODULES ARE:

• Sample inspected and tested per incoming shipment.

Notes: 

1. None

Technical Specifications