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

Mindstorm Microwave Motion Detection

DFRobot ( and available at produces a tiny 10-GHz Doppler radar called Microwave Sensor that offers interesting applications in motion detection. Most motion detectors (ultrasonic, passive infrared, lidar) sense the presence of something, but the Doppler radar senses things actually in motion. Moving objects create a Doppler shift that the microwave radar sensor detects. As in the video above, the radar can be connected to the Mindstorms EV3 Intelligent Brick. The Intelligent Brick supplies power to the radar and gives a light/audio indication when motion is detected. An advantage of using the radar is that it can see through surfaces like a door or wall to something moving on the other side of the surface. In the video below, motion through surfaces is detector with the radar wave passing through a cardboard box plus 2-centimeters of wood.

Detecting motion through a door is useful, as in the video below, noting that the alarm sounds as it detects motion through the door before the door opens. I might take this with me the next time I stay in a hotel for through-the-door security monitoring. The radar works well through wood, fiberglass, or glass. But one of the doors I tested was made with aluminum--the radar does not work through metal.

The connection of the microwave motion sensor is made as in my other blog post called “Reading Analog Voltage.” The software control is shown in the screenshot at the bottom of this page.

EV3 program for interface with Microwave Sensor.