> Well, 1.142 * 9.72340425532 - 9.95823902214 is 1.145. So I think the > value is properly scaled, just it happens that for your specific value, > the scaled value is almost the same as the original value, and that > confused you. Thank you very much Jean, that explains everything. I was incorrectly assuming the hidden least significant digit was 0, i.e. that the input was 1.140 V rather than 1.142 V, so I was expecting the conversion to result in 1.13 (1.1264). I should know better than to rely on tests performed on a Friday evening. > The limited resolution of "sensors" admittedly does not help here, try > "sensors -u" to see the 3rd digit. With my sensors version 3.2.0, the -u option changes the output format, but doesn't provide additional information. # sensors --no-adapter ads1115-i2c-2-4a ads1115-i2c-2-4a in4: -3.16 V in5: +0.70 V in6: +0.69 V # sensors -u --no-adapter ads1115-i2c-2-4a ads1115-i2c-2-4a in4: in4_input: -3.16 in5: in5_input: 0.70 in6: in6_input: 0.69 I assume it is supposed to print the raw information obtained from /sys # sensors --help | grep -- -u -u Raw output (debugging only) # cat /sys/bus/i2c/devices/2-004a/in?_input 699 696 692 > Note that you have a wrong factor in the second half Thanks for catching. When I first read http://www.lm-sensors.org/wiki/VoltageLabelsAndScaling I thought the value was in mV, after using it, I correct its use in first half, but not the second. On Tue, Sep 2, 2014 at 4:34 AM, Jean Delvare <jdelvare@xxxxxxx> wrote: > Hi Christopher, > > On Fri, 22 Aug 2014 18:31:22 -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. > > I tried but could not reproduce the bug here. I also looked at the > source code and there is no arbitrary limit to the number of digits. > > > root@centaur-3_0009:~# tail -2 /etc/sensors3.conf > > chip "ads1115-*" > > compute in4 @*9.72340425532-9.95823902214 , > > (@+9958.23902214)/9.72340425532 > > Note that you have a wrong factor in the second half here, even though > that's not related to your problem. > > > root@centaur-3_0009:~# sensors --no-adapter ads1115-i2c-2-4a > > ads1115-i2c-2-4a > > in4: +1.14 V > > in5: +1.14 V > > in6: +1.14 V > > Well, 1.142 * 9.72340425532 - 9.95823902214 is 1.145. So I think the > value is properly scaled, just it happens that for your specific value, > the scaled value is almost the same as the original value, and that > confused you. > > The limited resolution of "sensors" admittedly does not help here, try > "sensors -u" to see the 3rd digit. > > -- > Jean Delvare > http://jdelvare.nerim.net/wishlist.html > -- Chris _______________________________________________ lm-sensors mailing list lm-sensors@xxxxxxxxxxxxxx http://lists.lm-sensors.org/mailman/listinfo/lm-sensors
