We use an infrared camera of the type MLX90460 with a 50mm lens for three purposes:

• temperature cool cylinder
• temperature warm cylinder
• the flame burning

It'll take four components to build this sensor

A Housing for the Sensor (the Rocket)

The camera has to be placed 7 to 10 cm from the flame.

The camera has to have a fixed position in relation to the Stirling engine. The software will have to pick two rectangles out of the image. This is a static software configuration.

The Sensor

The MX90460 with a 50 mm lens It has a 32x24 pixel array. I got it from here.

The connector 3.0V does not get used. The camera gets powered with the VON cable.

Connector to the Camera and extension Cable

The wires to the camera can be directly soldered on. I decided to buy a small plug (4 Pin Dupont female). This cable is 150mm long. This is not long enough to connect it to the Raspberry. I had to put a 300mm long male-female 4 wire extension cable in between. This allows me to change the camera without having to solder. I have to switch colors in the wiring plan to connect to the Raspberry.

The information flow starts from 4 contacts from the camera. I pick it up with with 4Pin Dupont plug. I extend it with a male-female cable. This cable gets connected with the GPIO pins of the Raspberry.

The Wiring Schema

MLX90460	Connector Cable Color (arbitrary)	Cable Color (arbitrary)	Raspberry Pin	GPIO
VIN	Green	Green	1	3.3V
SDA	Purple	Purple	3	GPIO 2
SCL	Blue	Blue	5	GPIO 3
GND	Yellow	Yellow	14	GND
3.0V	-	-	-	-

 

Enable the Operating System

The sensor is using the I2C protocol. It needs to be enabled. Use the interactive "Raspberry Pi Configuration" tool and enable it in the "Interfaces" section. Reboot the Raspberry.

An alternative is to update /boot/config.txt with the following two parameters

dtparam=i2c_arm=on
dtparam=i2c_arm_baudrate=1000000

The first parameter will do the same as the interactive tool. The second parameter is a safety precaution to avoid bottlenecks on the bus.

Testing the Sensor

The took i2cdetect needs to be installed upfront:

pi@raspberrypi:~ $ sudo apt-get install -y python3-smbus
pi@raspberrypi:~ $ sudo apt-get install -y i2c-tools

Then use the command

pi@raspberrypi:~ $i2cdetect -y 1

It should list a table. The table has to have an entry "33" somewhere. The is the identifier of an MLX90640 sensor on the bus.

Enabling Greengrass V2 to access the Sensor

The Python scripts run as user ggc_user in Greengrass. Use the following command to allow ggc_user to access i2c:

sudo usermod -a -G i2c ggc_user

Enabling the Calibration of the Camera

The camera will be in different positions depending on the physical setup. The Greengrass component will install a a calibration program as well. This calibration will have to be run as root. The calibration program is written in Python3 and it will need a number of Python libraries. Install them with the command:

At this point, the MLX90640 is ready to be read by the Raspberry Pi. However, since the Adafruit library is being used, a few other libraries need to be installed:

pi@raspberrypi:~ $ sudo pip3 install RPI.GPIO adafruit-blinka
pi@raspberrypi:~ $ sudo pip3 install adafruit-circuitpython-mlx90640
pi@raspberrypi:~ $ sudo pip3 install matplotlib