IR Images Come to Your Cellphone

In this article Brian uses a Melexis MLX90640 IR camera module coupled to an ESP32 controller. He streams the image data to a web browser running on a cell phone, tablet, or computer, eliminating the need for a dedicated color LCD. Together, this makes for a very low-price IR camera.

- By Brian Millier

Forward-looking infrared (FLIR) cameras are quite common today. These cameras detect infrared energy, which is a measure of how much heat an object is emitting. FLIR sensors were developed in 1963 by Kirby Taylor, while working at Texas Instruments and were originally designed for military purposes. At the time, they would have been expensive and thus only practical for the military, which spends heavily for technology. In time, however, the cost of these sensors dropped enough to make them practical for commercial/consumer use.

Infrared light falls into two ranges: long-wave and medium-wave. Long-wave IR sensors can pick up body heat as well as heat produced by electronic components. They only work over a limited distance, which is generally fine for their intended purpose. These sensors are often referred to a “thermopile IR sensors.” Medium-wave IR sensors have other uses as well but generally need to be cooled to cryogenic temperatures.

Many years ago, I worked for General Electric Medical Systems. I serviced an IR camera system they sold, called the Spectrotherm. It was used for mammograms on female patients to detect breast cancer. If my memory serves me correctly, its IR sensor was made by the military contractor Hughes. As already mentioned, this sensor had to be maintained at minus 195°C by being surrounded by a vacuum vessel (dewar) containing liquid nitrogen. This wasn't as inconvenient as you might think, since hospitals use liquid nitrogen for many other purposes. The Spectrotherm's IR sensor was not at all like the modern IR camera sensors as it produced only a single pixel. To get an image, the incoming IR energy making up the image had to be bounced off two moving mirrors. This allowed for the scanning of the incoming IR energy in both the vertical and horizontal planes. This is similar in principle to the fixed bar code scanners you see in the grocery store checkout line.