Herb Peyerl Puts Location-Tracking AprilTag Fiducials to Work as a Motorized Gate Key System

Roboticist Herb Peyerl has turned to a somewhat unusual security mechanism for a motorized gate, in order to allow friends to gain access quickly and easily: an OpenMV-powered AprilTag recognition system.

"As part of some tinkering I was doing with my robotics team, I was learning about AprilTags," Peyerl explains in a blog post brought to our attention by Adafruit, referring to the visual fiducial system developed at the University of Michigan and commonly found in robotics projects. "Coincidentally, I had also recently installed a gate opener at the front gate and was struggling with how to organize guest access."

The solution, Peyerl decided, was to combine the two. Using an OpenMV smart camera module placed inside a recycled housing from an Axis surveillance camera, to provide weather-proofing, Peyerl created a simple authentication system: Wave a smartphone with an image of an authorized tag on the screen in the direction of the camera and the gate opens.

"I played with the QR Code recognition and various families of AprilTag," Peyerl notes. "While the QR Code recognition worked fine and allowed me some nice flexibility in terms of content, it was more fallible under varying light conditions. AprilTags are more robust and recognized pretty quickly from a few feet away."

"Obviously this isn't super secure," Peyerl admits, "but most people who are breaking into houses aren't sophisticated enough to know about fiducials. Most people will assume the camera is for someone in the house to remotely activate a switch."

The full Python source code for the project is available on Peyerl's blog under an unspecified open source license; source code for generating the AprilTags themselves can be found on the AprilRobotics GitHub repository.