sensors and bias

John Watlington wad at
Fri Nov 27 01:38:54 EST 2009

The bias for port B is used for port F (the DC input).
Port F has no bias generator, and would have to use
another port's, regardless of whether it was DC coupled or not.


On Nov 26, 2009, at 7:18 AM, Daniel Drake wrote:

> Hi,
> On XO-1, we had an ALSA switch that enabled mic bias. This was used by
> measure when being put into resistance sensor mode.
> However, on XO-1.5, when Mitch Bradley suggested how to implement  
> sensor
> mode, his advice was "disable bias, enable the DC port and select  
> it as
> input"
> Also, our DC input port does not seem to have any bias options.
> It is NID 0x1e.
> The only nodes that have bias options are 0x1a and 0x1b (the analog
> microphone inputs).
> Not knowing much about this area, I'm confused. Is bias useful or not
> when dealing with sensors? Have we excluded the possibility to control
> it on XO-1.5?
> (The current XO-1.5 kernel has a switch to control "DC Input Bias" but
> this was an oversight, it doesn't do anything because NID 0x1e has no
> bias settings.)
> Daniel
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