2017 REVIEW | 'IoT & Embedded MAKER SPACE - MKE' Group

MAX6675 Temp Module & Arduino

2017 OCTOBER | by Gene Casanova

Senior Systems Engineer

K Thermalcoupler & Arduino

Thermocouples are an industrial standard for accuracy measuring temperature.   Thermocouples are made in a wide range of physical configurations and measuring capabilities.

Cold junction compensation and detection of a very small voltage change, for every degree in change of temperature, are parameters required to get accurate measurements.

The MAX6675 IC chip, offers K type thermocouple functionality with an Arduino system.  The IC has been designed to measure the output from a K thermocouple, and output the data through a 'SPI' interface.  This SPI interface is ready to use on an Arduino systemboard.

The MAX6675 performs cold-junction compensation and digitizes the signal from a type-K thermocouple.  The data is output in a 12-bit resolution, SPI™-compatible, read-only format.  This converter resolves temperatures to 0.25°C, enabling readings as high as +1024°C, and exhibits thermocouple accuracy of 8LSBs for temperatures ranging from 0°C to +700°C.

Applications ● Industrial ● Appliances ● HVAC

● Direct Digital Conversion of Type -K Thermocouple Output

● Cold-Junction Compensation

● Simple SPI-Compatible Serial Interface

● 12-Bit, 0.25°C Resolution

● Open Thermocouple Detection

MAX6675ISA -20°C to +85°C, 8 SO package.

MAX6675 Specifications

CGI Computer Wares MAX6675 Module Pinouts

SO

Serial Output

CS

Chip Select. Set 'LOW', selects the module and triggers an output synchronized with a clock.

SCK

Serial Clock. Provided by an Arduino systemboard.

VCC

5 VDC. Typically provided by 5V output pin on Arduino systemboard.

GND

Ground. Provided by an Arduino systemboard.

-

Negative terminal of K Thermalcoupler.

+

Positive terminal of K Thermalcoupler.

K Thermalcouplers Color Code

BEWARE: Most K thermocouples come with a red lead and a yellow lead.

The red lead is normally the negative (-) connection; the yellow lead is positive (+); as an thermalcoupler-industry standard.

Thermalcoupler connections test - increase the temperature at the thermocouple tip.  Correct lead connection polarity, will provide an increase in temperature indication.  An incorrect (reversed) lead connection polarity will indicate a decreasing temperature.

CGI Computer Wares MAX6675 Module Arduino Sketch (C Source Code)

An Experimental Arduino Sketch and connection configuration:

Arduino  ---> Module

pin 10 ---> SCK

pin 9   ---> CS

pin 8    ---> SO

5V       ---> VCC

GND   ---> GND

/* EXPERIMENTAL
 * MAX6675 Arduino Termperature Reading
*/
#include "max6675.h"
int ktcSO = 8;
int ktcCS = 9;
int ktcCLK = 10;
MAX6675 ktc(ktcCLK, ktcCS, ktcSO);
void setup(){
   Serial.begin(9600);

   // Delay, enabling the MAX6675 establish steady data
   delay(500);
}
void loop(){
   // Basic Serial Output Test:
   Serial.print("Deg C = ");
   Serial.print(ktc.readCelsius());
   Serial.print("\t Deg F = ");
   Serial.println(ktc.readFahrenheit());
   delay(500);	// Delay.
}

Use The Technology Wisely & Keep It Simple

- Cheers!

Gene Casanova