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Changing sample rate breaks impedance measurement #94

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bmartin427 opened this issue Dec 5, 2019 · 2 comments
Open

Changing sample rate breaks impedance measurement #94

bmartin427 opened this issue Dec 5, 2019 · 2 comments

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@bmartin427
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Changing the sample rate seems to clobber the LOFF register (0x04) of the ADS1299. This can be easily reproduced by using the sequence of serial commands ?, ~6, and ? following reset. The LOFF register has the value 0x02 prior to the sample rate command, and 0x00 afterwards. This value change configures the ADS1299 for DC lead-off detection instead of 31.2Hz AC, which is not what the GUI expects to use.

This issue is the underlying cause of OpenBCI/OpenBCI_GUI#653. However, no wifi board is required to reproduce this issue as described above. Wifi is involved in the original issue only insofar as the GUI only attempts to change the sample rate at startup when using the wifi interface, and not serial.

@wjcroft
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wjcroft commented Dec 5, 2019

Brad, thanks very much for tracking this down.

bmartin427 pushed a commit to bmartin427/OpenBCI_Cyton_Library that referenced this issue Dec 5, 2019
Previously, this was only done at initial board reset, but this state would
get clobbered any time the sample rate was changed.

Also, this commit bumps the firmware version to 3.1.3.

Addresses OpenBCI#94.
@bmartin427
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I have confirmed that PR #95 makes the 31.2Hz waveform show up in the GUI using the wifi interface when clicking the 'ohm' icons.

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