Switching to 16 channels, the onboard accelerometer is multiplexed in firmware and clocked intermittently. How to recover it on the library side.
One detail traps those moving from 8 to 16 channels: the onboard accelerometer seems to vanish. Values drop to zero or freeze, and people assume a sensor failure. The hardware works, what changed is the allocation of the internal bus.
Why the sensor goes quiet
In 16 channels, each data frame must carry twice as many EEG samples in the same time window. The firmware no longer has room to insert the accelerometer axes on every sample. It switches to multiplexing: the axes are emitted intermittently, taking turns replacing auxiliary bytes in the frame.
The effective accelerometer rate therefore drops sharply and becomes irregular relative to the EEG stream.
Recovering it on the library side
The data is not lost, it is scattered. On the library side, you must decode the auxiliary channel by spotting the multiplexing markers, reassemble axes emitted across successive frames, then resample onto the EEG time base to obtain a continuous, usable stream.
The takeaway: in high-density mode, auxiliary sensors do not disappear, they go intermittent. Read the frame format before concluding a failure.