On Wed, Apr 21, 2021 at 10:05 PM Andy Shevchenko <andy.shevchenko@xxxxxxxxx> wrote: > > On Wed, Apr 21, 2021 at 1:14 PM Linus Walleij <linus.walleij@xxxxxxxxxx> wrote: > > > > On Tue, Apr 20, 2021 at 11:26 PM Dmitry Osipenko <digetx@xxxxxxxxx> wrote: > > > > > I found a non-kernel example > > > which uses a similar equation [1], but in a different form. The main > > > difference is that the Arduino code interprets a raw temperature value > > > as a signed integer, while upstream assumes it's unsigned. > > > > > > [1] > > > https://github.com/blaisejarrett/Arduino-Lib.MPU3050/blob/master/MPU3050lib.cpp#L111 > > > > Oh that's nice. Room temperature as mentioned is 20 deg C > > I think? > > > > The divide by 280 part seems coherent in all examples. > > > > > Still, even if assume that the raw temperature is a signed s16 value, it > > > gives us ~35C in a result, which should be off by ~10C. > > Actually here [1] it says in chapter 3.1 that room temperature is 35°C. > > Range: -30°C .. +85°C > Sensitivity: 280 LSB/°C > Room temperature offset: 35°C = -13200 LSB > > [1]: https://www.cdiweb.com/datasheets/invensense/mpu-3000a.pdf So, if I'm reading this and the register description right the value is in the range -32768..32767. -13200 defines 35°C 50000 as mentioned by Dmitry is actually -15536. So, it means that the more negative a value is the higher temperature is shown. Since it's linearized scale, now we can see that (13200 -15536)/280 + 35 gives us 26.66. Does it make sense? -- With Best Regards, Andy Shevchenko
