Please help with code for DS18B20

[Acetronics2]

Ok, Mel

You're talking resolution while I'm talking accuracy ...

DS already give .0625°C resolution ... but that do not mean anything because you only know you are inside the +/- 0.5 °C error gap.
LM 335 have your ADC resolution ... but always an "out of the box" +/- 0.5 °C precision

That is why I say ( and repeat ... ) you can't get a better reading WITHOUT a calibration ... or comparison with a known reference.

Even the MS5534 ( 16 bits! ) which comes with its calibration coeffs ... is given for a GUARANTEED +/- .8°C accuracy ...

For NTC's the problem is the +/- 5 to 20% value tolerance ... that need an individual curve adjustment to each sensor ( only 1 point ... yes... but one point calibration ! )


The only **predictable** High accuracy sensors are Platinium RTD's ... But , ... How much to pay for a class A probe ??? ...

Temp and Thermal measurements are always funny ... and make you humble !!!

Alain

[fratello]

Thank you for replays !!!
I wish to all a happy NEW YEAR 2009 !

I think I go crazzy with this little thermostat probleme ; I write ( based on Yours great codes) four routines ; everyone display a different temperature. Which of them is -in yours opinion - the best ?

1.OWOut DQ, 1, [$CC, $BE]
OWIn DQ, 2, [Temperature.Lowbyte, Temperature.Highbyte]
Convert_Temp:
Dummy = 625 * Temperature
TempC = DIV32 10
TempC = (Temperature & $7FF) >> 4
Float = ((Temperature.Lowbyte & $0F ) * 25 )>>2
Temperature = TempC*100 + Float

2.OWOut DQ, 1, [$CC, $BE]
OWIn DQ, 2, [RAWTEMP.Lowbyte, RAWTEMP.Highbyte]
Convert_Temp:
dummy = RAWTEMP * 625
TempC = DIV32 100
Temperature = TempC

3.OWOut DQ, 1, [$CC, $BE]
OWIn DQ, 2, [Temperature.Lowbyte, Temperature.Highbyte]
Convert_Temp:
TempC = (Temperature & $7FF) >> 4
Float = ((Temperature.Lowbyte & $0F ) * 25 )>>2
Temperature = TempC*100 + Float

4.OWOut DQ, 1, [$CC, $BE]
OWIn DQ, 0, [Temperature.LowByte, Temperature.HighByte, Skip 4, Count_Remain, Count_Per_C]
Convert_Temp :
Temperature = (((Temperature >> 1) * 100) - 25) + (((Count_Per_C - Count_Remain) * 100) / Count_Per_C)
if Temperature > 32767 then '32767 check if BIT12=1
Temperature= ~Temperature
temperature=temperature>>3 ; divide by 8

Thanks in advance for your support ; I hope I don't became boring !!!!

[Acetronics2]

Hi, Fratello

Too wide a question ... It's on your own now.

Here it's yours to take :

1) your Datasheets, and do not mix different sensors ( ! ), see how values are coded for each.

2) your PbP Manual, and look at how PbP can calculate and see where roundings can lead to ( small ...) outputted value differences.

...

Alain

[fratello]

I use the same sensor, the same circuit, just I re-write the code...the results are never the same...

[Gabestarting]

I intend to start tomorrow with the same project, using the same sensor DS18S20. May i use it without changing the code?

[Gabestarting]

Sorry, reading the text again i observed that i have the right sensor, i was lucky...So, the thermostat works fine, i am happy for the bas-file, however it is easier to understand than assembler. I made the circuit on a stripboard. Have a nice evening!

[fratello]

I want now to try to read the temperature with two sensors DS18B20 ; one for IN and other for OUT. It is possible ? How can I display both temperatures ?
Help, please !