Weight Based Intrusion Detection

As a bit of a swerve from my usual foray into automotive parts, I was asked by a previous employer if I could design a retrofittable solution for their range of security products to include a weight based detection system. They had been working on a solution for a year prior trying to detect people climbing onto the unit using a range of sensors, however weren’t able to get a reliable data output that was required to inform the security system if someone was actually attempting to climb onto, or over the gate.

In the overall scheme of things there were only a few design requirements:

• Be retrofittable to a specific range of access gates
• Require little to no modification to the existing gate chassis to ensure fitment in already installed locations
• Have a triggerable output to the gates main controller contact input
• Be able to reliably detect within a configurable weight range

As mentioned, the company did have some previous investigatory work into making a product, but the sensor accuracy wasn’t reliable enough, and the sensing solution itself required a lot of trial and error into perfecting the setup. A misalignment of 1° was enough to cause the system to not detect someone walking right in the path of the sensors, or more annoyingly, continuously detect false positives which would render the whole thing useless as it would be turned off within 5 minutes at that rate.

Rather than use a mix of ultrasonic and LIDAR sensors to detect presence of something on the gate, it was both easier to use pressure sensitive elements both from sourcing and retrofit aspects. After suitable locations were found on the gate chassis to mount the sensors, a small PCB and wiring loom were made up to complete the project.