From mboxrd@z Thu Jan  1 00:00:00 1970
From: Christopher Cordahi <christophercordahi@nanometrics.ca>
Date: Thu, 04 Sep 2014 02:19:51 +0000
Subject: Re: [lm-sensors] How to compute a voltage that may be positive or negative
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To: lm-sensors@vger.kernel.org

Thank you Guenter for your quick response and apologies for my slow
response.

Turns out I was the one confused.


On Sat, Aug 23, 2014 at 3:11 PM, Guenter Roeck <linux@roeck-us.net> wrote:

> On Fri, Aug 22, 2014 at 06:31:22PM -0400, Christopher Cordahi wrote:
> > I'm wondering if this is a valid use case.  I need to perform both a
> > multiplication and a subtraction to compute an original voltage.
> >
> > lm sensors 3.2.0 is working fine on Linux 2.6.39.4 reading an ADS1115 ADC
> > chip that measures a voltage from 0 V to about 2 V.
> >
> > # uname -srmo
> > Linux 2.6.39.4 armv5tejl GNU/Linux
> > # sensors --version
> > sensors version 3.2.0 with libsensors version 3.2.0
> > # sensors --bus-list ads1115-i2c-2-4a
> > bus "i2c-2" "i2c-1-mux (chan_id 0)"
> > bus "i2c-1" "DaVinci I2C adapter"
> > # sensors --no-adapter ads1115-i2c-2-4a
> > ads1115-i2c-2-4a
> > in4:         +1.14 V
> > in5:         +1.14 V
> > in6:         +1.14 V
> >
> > My problem is that I'd like for the sensor utility to convert the ADC
> > voltages to the original voltage which are in the range from about -10 V
> to
> > about +10 V.
> >
> > If I modify the sensor configuration as follows, it appears to work
> > correctly.
> >
> > root@centaur-3_0009:~# tail -2 /etc/sensors3.conf
> > chip "ads1115-*"
> >     compute in4 @*10-10 , (@+10)*10
> > root@centaur-3_0009:~# sensors --no-adapter ads1115-i2c-2-4a
> > ads1115-i2c-2-4a
> > in4:         +1.41 V
> > in5:         +1.14 V
> > in6:         +1.14 V
> >
> > Unfortunately when I adjust the values to their more accurate values, it
> no
> > longer converts and reports the original ADC value instead.
> >
> > root@centaur-3_0009:~# tail -2 /etc/sensors3.conf
> > chip "ads1115-*"
> >      compute in4 @*9.72340425532-9.95823902214 ,
> > (@+9958.23902214)/9.72340425532
>
> Maybe the sensors command gets confused with the number of digits.
> Can you try with less accuracy ?
>
> Guenter
>



-- 
Chris
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