Looks like one of the sensors broke:
That’s an IMU (Inertial Measurement Unit) with a dual accelerometer and a gyroscope. The gyro is the “big” one on the right. It senses rotation around the Z axis perpendicular to the board. The accelerometers are working fine, but the gyro appears to be toast. No matter what I try, it produces a noisy but fixed analog voltage. Connecting either of the self-test pins doesn’t doing anything.
Ouch, the gyro is also the most expensive part (in the €25..50 range). And this was a rather nice and sensitive one. Oh, well…
(that’s an Arduino with a battery pack by LiquidWare underneath, btw – so I can move this thing around and hook up the scope without having to attach power)