bno085-multi

Run two or more BNO085 IMUs on one microcontroller, simultaneously, at full rate. The stock Adafruit library cannot.

tiny_bno085.h is a single-header, dependency-free, fully reentrant driver for the CEVA/Hillcrest BNO085 (also BNO086 / BNO080) that reads the rotation-vector quaternion over I2C. Because it keeps all protocol state inside each object (no globals), you can instantiate as many sensors as you have I2C buses or addresses and stream them all at once.

Bench-run on a Teensy 4.1: two BNO085s at the library's default 100 Hz report rate, polled in the same loop as twelve AS5600 encoder channels and logged at 50 Hz.

Why this exists

The popular Adafruit_BNO08x library wraps CEVA's sh2 driver, which stores its state in file-scope globals: one sh2 context, one sensor-value pointer, one callback. It is therefore single-instance by construction. The moment you poll a second sensor, the shared state is clobbered and the blocking read hangs the whole sketch. This is a commonly reported problem with no clean fix in the stock library.

bno085-multi sidesteps it entirely: it speaks the BNO085's SHTP protocol directly in ~150 lines, with every byte of state living inside the TinyBNO085 instance. Nothing is shared, so nothing collides.

Features

• Multiple BNO085s at once, each at full report rate (tested: two at 100 Hz reports).
• Single header; only dependency is Arduino Wire.h.
• Non-blocking, bounded poll() you can call every loop pass next to other sensors.
• Rotation vector (orientation quaternion), the field most projects actually need.
• Tested on Teensy 4.1; portable to any Arduino-compatible I2C.

Wiring

Each sensor needs VCC (3V3), GND, SDA, SCL, and I2C-mode straps (PS0 = PS1 = GND). Two ways to run several:

• Different addresses on one bus: strap ADO low (0x4A) or high (0x4B).
• One bus per sensor (recommended): the BNO085 clock-stretches aggressively, so giving each its own I2C peripheral removes bus-level contention as well. This is how the reference rig runs, on the Teensy's Wire1 and Wire2.

This library fixes the software single-instance limit. The clock-stretch contention is a separate, hardware-level issue; separate buses solve both at once.

Usage

#include <Wire.h>
#include "tiny_bno085.h"

TinyBNO085 imuA(&Wire1, 0x4A);   // e.g. hand
TinyBNO085 imuB(&Wire2, 0x4B);   // e.g. forearm

void setup() {
  Wire1.begin(); Wire1.setClock(400000);
  Wire2.begin(); Wire2.setClock(400000);
  imuA.begin();
  imuB.begin();
}

void loop() {
  imuA.poll();   // non-blocking; refreshes imuA.qw/qx/qy/qz when a report arrives
  imuB.poll();
  // use imuA.qw..qz and imuB.qw..qz  (unit quaternion, order w, x, y, z)
}

See examples/dual_bno085 for a complete sketch.

API

member	description
TinyBNO085(TwoWire* bus, uint8_t addr)	construct on a bus and address
bool present()	does the chip ACK on the bus?
bool begin(...)	drain boot chatter, then enable the rotation vector
bool poll()	read one pending packet, non-blocking; true if one was consumed
float qw, qx, qy, qz	latest unit quaternion (w, x, y, z)
bool fresh	a quaternion has arrived since begin()

Scope and limits

Rotation vector only: no raw accel/gyro/mag, no calibration or activity reports. This is deliberate; the file is small on purpose. If you need the full sensor suite on a single BNO085, use the Adafruit library. Use this one when you need several BNO085s at once.

Origin

Written for TAKTO, an open-source hand exoskeleton with four instrumented fingers (M.Sc. thesis, Sebastian Molano, Hochschule Anhalt), where a hand IMU and a forearm IMU must stream together with twelve joint encoders. If it helps you, a star is appreciated.

License

MIT, see LICENSE.