BME280 sensor.

[HenrikOlsson]

Richard,
Out of curiosity, have you tried the PBP code you posted with negative temperature values?

The reason I ask is that my temperature compensation code was pretty much exactly like yours but it went belly up as soon as the temperature went below 0°C.
Reason mainly being the shift operations where potentially negative values (T2, T3 and therfor t_fine) are involved.

I see you're handling the compensation values quite differently, simply pushing them into the lower 16bits of a LONG no matter if they're positive or negative. With that said, both T2 and T3 are positive in my case, like in yours, but they could potentially BE negative and then I don't think simplt stuffing the "signed short" into the lower 16bits of our LONG will work properly.

I had to replace the affected shift operations with * and / at quite some cost for the execution time and for any compensation values specified as signed I'm doing this sort of thing:

    ' dig_T2, signed, read to temporary variable and cast to LONG to preserve sign of value
    SHIFTIN BME280_MISO, BME280_CLK, 6, [tmp_W.BYTE0, tmp_W.BYTE1]
        IF tmp_W.15 = 1 THEN
            dig_T2 = -ABS(tmp_W)
        ELSE
            dig_T2 = tmp_W
        ENDIF

/Henrik.

/Henrik.

[richard]

Out of curiosity, have you tried the PBP code you posted with negative temperature values?

sorry no, i never actually used pbp for these sensors after discovering the real potential of esp chips


if the upper word was set appropriately here maybe that would help , adc_t might need similar treatment but the calculation should be
then ok ,i think?

    T1.Byte0 = IIC_RX[0]                            ' Calibration data into Unsigned Word
       T1.Byte1 = IIC_RX[1]
    T2.Byte0 = IIC_RX[2]                            ' Calibration data into Signed Long
       T2.Byte1 = IIC_RX[3]
    if  IIC_RX[3].7 then 
      T2.Byte3=255
      T2.Byte4=255
    else
      T2.Byte3=0
      T2.Byte4=0
    endif
    T3.Byte0 = IIC_RX[4]                            ' Calibration data into Signed Long
       T3.Byte1 = IIC_RX[5]
    if  IIC_RX[5].7 then 
      T3.Byte3=255
     T3.Byte4=255
   else
      T3.Byte3=0
      T3.Byte4=0
   endif

[richard]

the calculation should be
then ok ,i think?

nah, pbp needs a signed shift right command too. too hard me thinks. pic chip in bin, esp wins

[HenrikOlsson]

For anyone who are still interested in using this sensor with PBP I've posted my code as an example in the Wiki:
http://www.picbasic.co.uk/forum/cont...BME280-Example

If any questions or suggestions should pop up I suggest we keep them in this thread.

/Henrik.

[richard]

excellent work henrik, way better than my fp attempt [nearly 10k in size] to get a result.
i confirm it gets same results temp and pressure wise as arduino calcs for same input data
not tried hum yet

[richard]

henrik
i made a little change

used this style
IF P2.15 = 1 THEN
p2.highWORD = 65535
ENDIF

for all the casts to long , it saves a worthwhile bit of code space

can't test humidity on pic yet , just discovered the dishonest ebayer has sold me 4 out of 5 bmp280's in lieu of bme280 boards.
i can't tell them apart with naked eye, must admit the temp seems more accurate in absolute terms for the bmp boards there is nearly a 3 deg difference between bme and bmp readings in the same aircon'ed room and thats closer to the mercury bulb . are cheap ebay things always a bit dodgy?

[towlerg]

"are cheap ebay things always a bit dodgy?" not in my experience, most seem surprisingly interested in protecting their feedback score. Try email seller thro ebay and explain the mistake.