We now have a new category in the IMU world: Bosch Sensortec has announced the first of what they call Application-Specific Sensor Nodes, or ASSNs. They have dubbed this particular device an Absolute Orientation Sensor. It looks strikingly like an all-in-one sensor hub, with an accelerometer, a gyro, a magnetometer, and a 32-bit ARM-based microcontroller (source not disclosed).
The difference is that a sensor hub per se leaves the software to be executed on the micro pretty wide open for the user to define. The BNO055, by contrast, is really intended to combine the motion sensors via built-in fusion on the micro so that it looks like a higher-level orientation sensor. It essentially bumps up the level of abstraction, burying the sensors and micro inside something more akin to a black box. Data is communicated pre-computed as quaternions rather than raw.
Power is addressed by allowing a stand-by mode where the gyroscope – always the power hog – can be put to sleep. When the accelerometer detects motion, it can then wake the gyro – which responds in a few nanoseconds – so that it can intercept any rotational motion. This assumes, of course, that any rotation missed during that wake-up is negligible. (Quick math sanity check says that if an object rotates, say, 6 degrees in 10 ns, then that’s 60 degrees in 100 ns or a full rotation in 600 ns… divide by 10 to get 60 ns, multiply by a billion to get 60 s, so that would be 100,000,000 RPM… yeah, not even Washington DC can spin anything that fast…)
So full power is around 11 or 12 mA; in motion-wakeable stand-by it goes down to 150 µA. If you put everything to sleep and wake it through I2C instead, you can get down to the 20-µA range.
You can find more on this device in their release…