Affordable Intelligent Contactless IR thermometer

Original idea is to use big 7-Segments display for better visibility and price. After revising design, I decide to use 8x8 dotmatrix display with driver MAX7219. These module are cheap and also good for displaying symbols, character.

So, revised design V1.2 is as follow.

MAX7219 modules can be cascaded easily to expand digits. There are a lot of Arduino driver to interface this module. I selected the following Lib science many functions and modules are supported.

Lib:

https://github.com/MajicDesigns/MD_MAX72XX

MAX7219  Connection:

• Vcc -  ESP32 3.3V
• GND - GND
• DATA - ESP32 23
• CLK - ESP32 18
• CS - ESP32 15

LED:

• NORMAL LED - ESP32 25
• WARNING LED - ESP32 26
• ALERT LED - ESP32 27
• BUZZER 14 - ESP32 14

Schematic :

Added LED and buzzer functions.

When I moved my finger near ir+distance sensor, the result is like that. Symbol C is not displayed full digit. Required additional display or tweak fonts?

V1.2 Code was added to my github, though I need to clean and touch code more.

https://github.com/oakkar7/AVCTV1

The first idea was to use MAX1719 display driver. But due to late delivery of my parts order, I have tested with inhand TM1637 4 Digits 7 segment display driver module. Quick google search and after test, temperature is shown successfully in Deg C. 

Lib use: https://github.com/avishorp/TM1637

Connection:

Vcc - 3.3V

GND - GNE

CLK - ESP32 18

DATA - ESP32 19

# Note : Need to find out a way to enable single dot for decimal point. (or) MAX1719 with 8x8 dot matrix display?

The idea of design V1 is automatic measurement when object is closed to sensor. MLX90614 sensor reading distance is 2~5mm. So, IR reflected sensor TCRT5000 is used to measure proximity distance. Circuit is simple. Analog out is connected to ESP32 pin 34 (ADC input).

Changed the code snip a little to measure if threshold ADC reading is changed. When the hand is closed to IR sensor and IR reflected sensor, temperature measurement is performed.

TCRT5000  Connection

Very rough test circuit for now :) 

The first step is to test MLX90614 sensor with ESP32 dev (Node MCU) board. Test is straignt forward. By using Adafruit Adafruit-MLX90614-Library, sensor was simply tested by UART output.

Lib Link: https://github.com/adafruit/Adafruit-MLX90614-Library

Connection :

VIN -> ESP32 3.3v
GND -> ESP32 GND
SCL -> ESP32 22
SDA -> ESP32 21

My first idea is to use Infrared Thermal array sensor like MLX90640 with powerful MCU.  But my DHL order is stuck and on hold on the way. Meanwhile waiting the main parts, I like to start the project V.1 with inhand parts.

The system design of V.1 is simple.

• Use ESP32 (may extend the Camera support later)
• MLX90614, single dot contactless IR thermal sensor which widely used by many arduino and DIY project
• Infrared distance sensor (pair of IR LED and Photo Diode) to measure target body distance under test
• 7-Segments LED display with MAX7219 driver (Rather than LCD or OLED, it is cheap, clearly visible under day light and durable)
• R, G and B Led , to alert normal, warning and critical temperature condition
• A buzzer to beep alert sound
• Used as wall mount or with a tripod stand

Working Principals 

When a target under test is closed to measurement range, ( measured with IR reflection sensor) temperature is measured and displays automatically

If temperature is normal, Green LED will light on with a buzzer single beep, if not  Warning Yellow or Red LED will be flashed depends on temperature and buzzer will beep noticeable tone.

Fig 2. Version-1 System Design