Creating an infrared thermometer with a Wemos Mini and a MLX90614

In this example we will create a basic infrared thermometer using an MLX90614 and Wemos Mini (ESP8266) and an OLED

This was created basically of the current virus scare – not to make money but as hopefully a useful little electronic addition to check your temperature

Here is the human temperature range from Wikipedia

The MLX90614 is an infrared thermometer for non-contact temperature measurements. Both the IR sensitive thermopile detector chip and the signal conditioning ASIC are integrated in the same TO-39 can. Integrated into the MLX90614 are a low noise amplifier, 17-bit ADC and powerful DSP unit thus achieving high accuracy and resolution of the thermometer.

The thermometer comes factory calibrated with a digital SMBus output giving full access to the measured temperature in the complete temperature range(s) with a resolution of 0.02°C.

The user can configure the digital output to be pulse width modulation (PWM). As a standard, the 10-bit PWM is configured to continuously transmit the measured temperature in range of -20 to 120°C, with an output resolution of 0.14°C.

Features

• Factory calibrated in wide temperature range: -40 to 125°C for sensor temperature and -70 to 380°C for object temperature

• High accuracy of 0.5°C over wide temperature range (0..+50 C for both Ta and To)

• Medical accuracy of 0.1°C in a limited temperature range available on request

• Measurement resolution of 0.02°C

Schematic

I connected an OLED shield to the Wemos Mini and the MLX90614 breakout to the oled shield

Parts Required

No affiliate links – this is information in the time of a health crisis where even the ability to create an accurate thermometer could be important. Not cashing in on this.

You can find these parts on many sites

Code example 1

This first example uses the Adafruit MLX90614 library  and is the default example. You can add the library using the Library manager in the arduino ide

Source code

#include <Wire.h>
#include <Adafruit_MLX90614.h>
 
Adafruit_MLX90614 mlx = Adafruit_MLX90614();
 
void setup() {
  Serial.begin(9600);
 
  Serial.println("Adafruit MLX90614 test");  
 
  mlx.begin();  
}
 
void loop() {
  Serial.print("Ambient = "); Serial.print(mlx.readAmbientTempC()); 
  Serial.print("*C\tObject = "); Serial.print(mlx.readObjectTempC()); Serial.println("*C");
  Serial.print("Ambient = "); Serial.print(mlx.readAmbientTempF()); 
  Serial.print("*F\tObject = "); Serial.print(mlx.readObjectTempF()); Serial.println("*F");
 
  Serial.println();
  delay(500);
}

Here is the output in the serial monitor

Ambient = 25.81*C Object = 25.11*C
Ambient = 78.46*F Object = 77.20*F

OLED Example

Now as you will have seen from the description we are ultimately trying to display the temperatures on an OLED

You need https://github.com/sparkfun/SparkFun_Micro_OLED_Arduino_Library

Source code

#include <Wire.h>  // Include Wire if you're using I2C
#include <SFE_MicroOLED.h>  // Include the SFE_MicroOLED library
#include <Adafruit_MLX90614.h>
 
#define DC_JUMPER 0  // I2C Addres: 0 - 0x3C, 1 - 0x3D
#define PIN_RESET 255 
 
Adafruit_MLX90614 mlx = Adafruit_MLX90614();
MicroOLED oled(PIN_RESET, DC_JUMPER); // Example I2C declaration
 
 
void setup() 
{
  Serial.begin(9600);
  mlx.begin();
  oled.begin();
  oled.clear(ALL);  // Clear the display's memory (gets rid of artifacts)
  oled.display();  
}
 
void loop() 
{
  // Wait a few seconds between measurements.
  delay(2000);
 
  oled.clear(PAGE); 
  oled.setFontType(0); // set font type 0, please see declaration in SFE_MicroOLED.cpp
  oled.setCursor(1, 3);
  oled.print("Ambient: ");
  oled.setCursor(1, 12);
  oled.print(mlx.readAmbientTempC());
  oled.print(" %\t");
  oled.setCursor(1, 21);
  oled.print("Object :");
  oled.setCursor(1, 30);
  oled.print(mlx.readObjectTempC());
  oled.print(" *C ");
  oled.display();  
}

Here you can see the setup in action

You could design a box for this with an external power source, we will be looking at other sensors and other microcontrollers as well

Links

https://www.melexis.com/en/documents/documentation/datasheets/datasheet-mlx90614