The Wand Chooses the IMU - Open Source Hardware for Synchronising Wearables using Magnetometers

This paper presents the Synchronisation Wand, an open-source hardware solution which can be used to synchronise multiple inertial measurement unit sensors (IMU) using their onboard magnetometers. The wand is based on commercial off-the-shelf components with standard 4-layer PCB manufacturing and self-service assembly. The case can be 3D printed using any Fused Filament Fabrication (FFF) based printer. The system combines an ESP32-S3 micro-controller unit with an electromagnetic (EM) generator to create an encoded EM event which can be used to synchronise multiple IMUs. The hardware includes an onboard IMU allowing the user to track the motion of the wand as well as perform kinetic synchronising events. The device also includes an OLED display and 4 configurable tactile switches to enhance the usability of the system. We demonstrate the device's capability to generate an encoded EM pulse which can be used to reduce the maximum synchronisation error between two IMUs down to 10ms.