DS18B20 ID saving To and Reading From EEPROM

[Heckler]

snuff28,

Sorry for my short reply... I tossed it out while at work.

'=============================================================
'           Read Temp Sensor and convert to deg F
'=============================================================
GetTemp:
    OWOUT  Comm_Pin, 1, [$CC, $4E, 0, 0, DS18B20_9bit]  'set resolution of sensor
Start_Convert:
    OWOUT  Comm_Pin, 1, [$CC, $44]' Skip ROM search & do temp conversion

Wait_Up:
    OWIN   Comm_Pin, 4, [Busy]    ' Read busy-bit
    IF     Busy = 0 THEN Wait_Up  ' Still busy..?, Wait_Up..!
    OWOUT  Comm_Pin, 1, [$CC, $BE]' Skip ROM search & read scratchpad memory
    OWIN   Comm_Pin, 2, [Raw.byte0, Raw.byte1]' Read two bytes / end comms

    '--------------  Convert_Temp: -----------------------
    Sign="+"
    IF Cold_Bit = 1 THEN    'it's below zero Celsius
      C=(ABS Raw>>4)*-10      'so shift the ABS value right and mult X -10
      ELSE
      C=(Raw>>4)*10           'else shift value right and mult X 10
    ENDIF

@ CtoF _C, _F             ; Convert Celsius to Fahrenheit
        'converted value will be X 10, ie. 756=75.6 deg F
        'so devide by 10 to get whole degrees

    IF f.15=1 THEN Sign="-" 'if converted value is below zero F then sign is "-"
    TempF = (ABS f)/10      'take tha ABS value and /10
    IF f//10 >4 THEN TempF=TempF+1 'check remainder, if >4 then round up
return      'with TempF containing current temperature

here is a snippet of code that I use in a little project. It's been a while since I wrote it (mostly borrowed from Bruce at Rentron and some help I think from Darrell) and I havent studied it lately either.

But it is agnostic of the device (DS18b20) serial number.
It works with any sensor I install.
I'm guessing that I am able to do that because I am only reading one sensor.

I suspect that if you are trying to read multiple sensors then you have to use the device serial number to address the specific sensor.

Unless you attach only one sensor to a given PIC pin. Then I think you could ignore the device ID.

[Charlie]

If you simply want to be able to swap devices in case of failure (talk to one device at a time only) then don't bother with the serial number at all. You can distinguish the temperature sensor from other types of one wire devices by the family code (if you are building a weather station or something). If you need to talk to a few devices, separate one wire busses on different pins will work for a small number of devices.

[Ioannis]

Maxim has an application note for searching serial numbers of unknown devices. Please see the attached pdf file. It includes the algo and C code (sorry no PBP code yet).

Hope this helps,
Ioannis

[Dave]

Ioannis, Attached is a routine I wrote some time ago that searches for any 1 Wire device and displays them no mater how many are on the bus. Enjoy....

[Ioannis]

Hi Dave,

nice job and thanks for posting. Snuff28 and others, I am sure will be happy!

Ioannis

[snuff28]

Thanks Dave! The routine is awesome! Hopefully I will have some time this weekend to play with it.

Ioannis: thanks for pointing out the AN187 Search Serial number.pdf, it‎ made Daves routine make sense.

[Charlie]

So suppose I want to make indoor/ outdoor thermometers for all my family and friends as gifts. I'll have 2 DS18B20's on a bus in the design. How do I resolve which is the indoor one and which is the outdoor one?