Non-contact body temperature measurement using MLX90614 sensor
In the previous two articles in this tutorial series, I demonstrated how to display data from analog sensors (such as POT, LM35, soil moisture sensor, etc.) or data from smart digital sensors (DHT11) on TFT LCD.
In this third article, I will explain how to display body temperature on a TFT LCD. It uses an MLX90614 non-contact temperature measurement sensor. It is a complete non-contact body temperature measurement system built using an MLX sensor, TFT LCD, button (for taking reading measurements), LED, buzzer (for indication), etc. The complete system is built around the Arduino NANO development board.
The circuit diagram is followed by its connection, functioning and operation.
Circuit Diagram
The figure shows that the circuit is built using an MLX90614 sensor, buzzer, button, Arduino NANO board and TFT LCD.
Circuit Connections
The MLX sensor has four interface pins (1) SDA, (2) SCL, (3) Vcc (4) Gnd. The SDA and SCL pins are for IIC communication. The sensor works on the IIC protocol, so these pins are connected to the IIC pins A4 (SDA) and A5 (SCL) on the Arduino board. The Vcc pin is connected to the Arduino's 5V pin and the Gnd pin is connected to the circuit's ground.
The TFT LCD has a total of eight pins. It works on the SPI protocol. Thus, its pins are connected to the SPI pins of the Arduino board.
An LED is connected to pin A2 of the Arduino board for indication. As shown in the figure, a button is connected to digital pin D2 and the buzzer is connected to pin D3 for audio indication.
The Arduino board provides 5V output to the MLX sensor and TFT LCD. A 9V battery powers the circuit. This 9V is supplied to the Vin pin of the Arduino board.
Circuit operation
The operation of the circuit is very simple. We must point the MLX sensor at anyone's forehead (5 cm away) and press the button. The sensor will measure the person's body temperature. The Arduino reads body temperature and calibrates it. It accurately displays body temperature value on the TFT LCD in Centigrade ( óC ) and Fahrenheit ( óF ). The LED flashes whenever a new value is read and displayed, and the buzzer beeps.
How the MLX sensor measures body temperature and how the Arduino reads this temperature from the MLX sensor is explained in my article here:
This temperature value is converted to a string and an array of characters. Finally, Arduino displays this body temperature as characters on the TFT LCD. Arduino has the TFT library “TFT.h” which is used here along with two other libraries, “SPI.h” and “wire.h”
The Arduino TFT library has direct functions to display TEXT, graphics, images, etc., in various colors on the TFT LCD. TFT LCD works in SPI. So to communicate with TFT LCD we need SPI library and wire library
Here is the software program on Arduino IDE to display body temperature on TFT LCD
Here is the summary of the circuit arrangement and its working.
Youtube video link for this article
In the next article in this tutorial series, I will explain and demonstrate a distance measurement system using TFT LCD and UDM HC SR04 sensor.