Build your own ODKI-VBT.
A handful of parts, a 3D-printed shell and some soldering. Everything is on GitHub; this page is the short version.
About €26 with the board bought from DigiKey Italy (Oct 2026); roughly €20–60 depending on where you buy the Seeed XIAO board, which is most of the cost. Batteries, magnets and switches often come in multipacks, so the first build costs more out of pocket. Check the BOM ↗.
Before you start: this is not a beginner-friendly first electronics project. Short-circuiting, puncturing or reverse-wiring a LiPo can cause a fire. The design and instructions are provided as-is, with no warranty, and you build at your own risk.
| Part | Qty | Notes | Approx. cost |
|---|---|---|---|
| Seeed Studio XIAO nRF52840 Sense | 1 | nRF52840 + onboard 6-axis IMU, USB-C, LiPo charging | ~€14–52 by seller (€17 at DigiKey Italy, Oct 2026) |
| LiPo battery, 400 mAh, size 602035 | 1 | Must have a built-in protection circuit | ~€3.65–4.50 (packs) |
| Neodymium disc magnet, 10 × 2.2 mm | 3 | ~2 kg pull each | ~€0.21 each (packs) |
| SPDT slide switch SS12D00-G3 | 1 | Power switch | ~€0.05 (packs) |
| Thin hookup wire | 2 × ~4 cm | 26–30 AWG | negligible |
Printed shell: case-top + case-bottom | 1 set | From the CAD files | about 10–12 g of PLA |
Costs from the public bom.csv ↗, read in October 2026.
01–02Wire the switch and the battery
Solder the switch between GND and D6 (the firmware's wake pin), then the battery to the B+ / B- pads. Double-check polarity first.
03–04Flash, then prepare the shell
Flash the firmware with the Arduino IDE. Glue the three magnets and the battery into the printed case-bottom.
05–06Mount the electronics, close provisionally
Seat the board in case-top and close the shell without glue for now.
07–08Test it, then close it for good
Pair it with the app and run the functional test. Only when everything works, glue the shell shut.
Over USB the sensor logs every sample at 100 Hz. The repo has a Python log viewer and a replay tool that runs the real tracking engine on your computer.
Built one? Finish it with a Founders case.
A zip case designed for the ODKI-VBT sensor, laser-engraved. €19, tracked EU shipping €9 Italy / €12 rest of the EU, max 3 per order, voluntary 14-day return (case price refunded; shipping is not).
Licences: hardware CC BY-NC-SA 4.0, firmware GPL-3.0 + Commons Clause. Build, modify and share for non-commercial use; selling assembled units is reserved to ODKI. Details.