Jee Labs Talk

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1. smihai
   

   Hello,
   

        I've just got the pressure plug outside where it's ~ -10 Celsius but i've not manages to get the reading accordingly ... i think it need a little hacking or work with the data-sheet (the example in the sketch just gets all messy when it goes below 0)
   
        Any ideas.. ?

   Posted 22/01/2010 19:26:39

2. jcw
   

   Are the pressure readings still correct?

   Posted 22/01/2010 19:30:07

3. smihai
   

   yes (the pressure is still ok).
   when i take it outside they just get lower and lower and when they go below 0 they get started from a large value. it's a unsigned thingie i guess

   Posted 22/01/2010 19:34:53

4. jcw
   

   I understand temp is wrong, but is the pressure value still ok, even when the temp is wrong?

   Posted 22/01/2010 19:36:55

5. smihai
   

   about half an hour, 45min. later it went under 0 with a -2 reading.
   might it be the sensor response time... :-?

   Posted 22/01/2010 19:37:00

6. smihai
   

   yes. the pressure is ok even when the temp is wrong

   Posted 22/01/2010 19:39:07

7. jcw
   

   Ok, try this - in Ports/PortsBMP085.cpp, change line 41 from:
   

       int32t ut = meas[TEMP], up = meas[PRES];
   
   to
   
       int32t ut = (int16t) measTEMP], up = meas[PRES];
   
   I'm not sure that'll fix it, though. I can't easily test here, it's not freezing right now...
   Something else to try, print out the temperature in HEX and let me know what comes out:
   
       Serial.println(tval, HEX);

   Posted 22/01/2010 19:47:09

8. smihai
   

   Here's what i've got:

   BMP 29828 44023 -19 101606
   raw temp in hex: 7484
   temp calculated in hex: FFFFFFED

   and there aren't -19 more like -8 at most now
   and it keeps going down, -57 and going even lower now...

   Posted 22/01/2010 19:58:27

9. jcw
   

   Doesn't "-19" mean -1.9°C ?

   Posted 22/01/2010 20:12:36

10. smihai
    

    YES YES YES :)) jeez it was an easy one, i really forgot about it. THANKS A LOT !

    i've attached another pressure probe in another place just to see if there is something to do with local conditions

    Posted 22/01/2010 20:16:42

11. smihai
    

    it's a bit wired, i think that at times it does not have the value that is supposed to be after the dot.
    any idea on how i can split the value so that i can print it like a floating value, i remember something like shifting bits that i learned in college :-?

    another bad point for this sensor is that it takes a rather long time to get to the ambient temperature when shifting through big temperature differences, maby it is it's internal algorithm

    Posted 22/01/2010 20:21:19

12. smihai
    

    hmm. now i get some funky values again, something like
    BMP 33247 42676 -2669 51876
    BMP 33222 42692 -2670 51880

    And it's indoor and it's around 23degrees. when i try to heat it with my hand it goes down a bit, and when i blow air on it it gets to -1000 and the pressure get around the normal value...

    Any thought... any chance it broke during last night freezing temperatures?
    The funny thing is that i've tried a couple sensors with a couple of different boards and they all have this behavior :-?

    Posted 23/01/2010 13:14:58

13. smihai
    

    apparently when i uploaded the Ports library i entered one with a file that had some modifications made by me and they were not working. now it words all like a charm :))
    --any idea if i can delete older comments ?

    Posted 23/01/2010 14:06:05

14. jcw
    

    On this forum? No - you can't turn back history :)

    I was going to suggest undoing the change to line 41 which I proposed earlier, since that probably caused the problem.

    Posted 23/01/2010 16:06:48