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 > > Certainly a manual calibration is an option, but we will try to wait for > > the answer from Nathans and Jean-Baptiste before going that route. > > The method I have seen used is: > - Collect many bags of silica gel, those little packages of "dryer" that > come in shoe boxes. > - Put the device with all these in two layers of plastic bags and pull out > cables, glue or strap many layers around the bags to make it really tight > where the cables come out. > - Submerge this into a mixture of ice and water which is known to be > a calibration point for 0 degrees C, wait for some hour or so to > stabilize, add some ice if it all melts. > > Now measures should be 0 deg C so any deviance will be the constant > offset that need be added for the sensor. -- With Best Regards, Andy Shevchenko
