Lego Sherlock Holmes figure focuses a light beam on a Lego criminal with a small magnifying glass.

LEGO Scanning Infrared Thermometer

A radiometer (see my blog post on LEGO Radiometer) can be configured to measure the temperature of an object without physical contact. Temperature is determined in this technique by measuring the level of infrared radiation emitted by the object. Handheld infrared thermometers can be purchased in the $100 range. Now there’s a Mindstorms compatible infrared thermometer available from mindsensors.com. I attached one of these new sensors to a motor to scan an area. To provide an indication of observed temperature, and create a new type of decorative table lamp, I used another new release from mindsensors.com of an LED light strip called EV3Lights. Mindsensors.com provides programming blocks that can be imported into the EV3 programming environment, making software control easy to implement. I wrote a program that compares observed object to ambient temperature (also measured by the IR Temperature Sensor as an added feature). The program changes color displayed on the EV3Lights, with warm objects tending to red and cold object tending to blue. Observed object temperature close to ambient temperature gives a green setting. In the video above, the device is scanning a scene that includes a cup of hot tea and a glass of ice water. The EV3Lights go red when scanning across the tea cup and blue when scanning across the water glass.

The IR Temperature Sensor works well, but it should be understood that the observed temperature can have some error due to assumptions made in converting infrared power measurements to temperature. This is not a flaw of the sensor, but subtlety in the physics involved with radiometry. The mindsensors.com programming block for the IR Temperature Sensor provides a way to recalibrate the sensor for better accuracy, if the radiometric property of emissivity is known for the object being measured. The EV3Lights sensor had problems with the first unit I purchased, but the company was responsive in fixing the issue. EV3Lights comes with 5-m length of LED strip that can be cut to the length needed, though the cut is permanent. The discarded length of LEDs can’t be used again.