Valentyn's Watch-Like Open Source Full-Body Tracker Aims to Deliver Better VRChat Immersion

Designed for affordability and a long battery life, this STMicro STM32WB-based tracker could be made for just $25.

Pseudonymous electronic engineer "Valentyn" is working on a watch-like full-body tracker, designed with VRChat in mind, to provide better immersion in virtual reality — linking an inertial measurement unit (IMU) with an STMicroelectronics STM32WB microcontroller.

"Each tracker monitors its rotation in space, and the software uses your proportions and the coordinates of the VR headset to calculate joint angles and estimate limb positions," Valentyn explains of the core concept, which has already been proven in devices including the SlimeVR and HaritoraX. "Speaking more technically, the technology relies on absolute orientation sensors, a calibrated skeleton model, and forward kinematics."

Finding "certain shortcomings" in the SlimeVR, Valentyn set about building an alternative — targeting an active working time of 48 hours per charge. "As I plan to power the device from a battery, and a very small one at that, the [Espressif] ESP32, which consumes about 90mA even in Rx mode, is clearly not my choice," the maker explains."Having the most experience working with STM32, my choice fell on the STM32WB series. These are ultra-low-power MCUs [Microcontroller Units] that support the BLE [Bluetooth Low Energy] 5 standard, as well as wireless protocols [IEEE] 802.15.4."

Settling on the STM32WB15CCU6, thanks to its low price and ready availability, Valentyn paired the microcontroller with a TDK InvenSense ICM-42688-V six-axis MEMS inertial measurement unit, which combines a three-axis gyroscope with a three-axis accelerometer. With the addition of a MEMSIC MMC5983MA magnetometer, the sensor package was complete.

"[The PCB] is quite simple," Valentyn writes. "We have several sensors, DC-DC converters, a charging controller, etc. Just remember, the device is powered by a battery and we want to save as much charge as possible, so even for the resistor divider for measuring the battery voltage, I put MOSFET switches. The round board with a diameter of 40mm accommodates all components including the antenna, [and] a tiny OLED display with a resolution of 72×40 was added more for the sake of convenience in debugging."

Valentyn estimates that in a production run of 100 trackers, the parts — including a plastic housing and a strap to hold it to the user's body — would come to around $25 per unit. More details are available on the maker's page — but while Altium project files and software details have been promised, they had yet to be published at the time of writing.

Gareth Halfacree
Freelance journalist, technical author, hacker, tinkerer, erstwhile sysadmin. For hire:
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