Help with DS18B20 Code

Sassy · 2007-12-13 14:12

Hi All and Merry Christmas,

I have purchased a PicAxe one-wire Controller from Mr Anderson. I am using his example program to display Temperatures. The Code is fine for
displaying Temperatures above 32 Degrees, but when it gets below or at 32 Degrees Two things happen. SignBit for Negative Temperatures gets displayed at or Below·32 Degrees and the second problem I have is that when Temperatures are below 32 Degrees the Program starts Adding upwards as the Temperature decrease below 32 Degrees. I realize that Mr Andersons program is dealing with Degrees C, but I did insert x=x+3200 to try and convert to F. It does produce fairly accurate temperatures aboue 32 Degrees.... Any Help to solve these two problems would be appreciated.
Thank You in advance
Sassy

'Now do the Calculations

··· SignBit = X / 256 / 128
··· IF SignBit = 1 THEN ' its negative
······ X = X ^ $ffff + 1 ' take the two's comp
··· ENDIF
'Multiply by 11.25 - This is 100 * Tf
··· Y = X / 4··································································· '0.25
··· X = X * 11 + Y
··· x = x + 3200································································ 'Add 32 degrees·************
··· Whole = X / 100
··· Fract = X // 100

Chris Savage · 2007-12-13 17:59

Is this for a PICAXE or a BASIC Stamp?

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Chris Savage
Parallax Tech Support

Sassy · 2007-12-13 18:44

Sorry Chris,

The PicAxe is the remote 1-wire device. Here is the completes Code for a Basic Stamp that Ph Anderson uses as an example. Problem I have I want to be able to view below 32 degrees and negative Temperatures.

Basic Stamp (BS2) Routines

DS18B20_1.BS2

' {$STAMP BS2}' {$PBASIC 2.5}' DS18B20_1.BS2 (Basic Stamp 2)'' Illustrates the use of the ONEWIRE PIC in interfacing with a DS18B20 on' Channel 0.'' BS2-IC ONEWIRE PIC +5 VDC' |' P8 (term 13)

> "RX" (term 5) 4.7K DS18B20' P7 (term 12) <

"TX" (term 6) |' "0" (term 13)

DQ (term 2)' OPEN --- "BAUD" GRD ---- (term 1)' GRD ---- (term 3)'' 9600 baud.'' Copyright, Peter H. Anderson, Baltimore, MD, Nov 14, '06 BaudMode CON 84 '9600 True X VAR Word Y VAR Word SignBit VAR Byte Whole VAR Byte Fract VAR Byte DIR7 = 0 ' serial input DIR8 = 1 ' serial output OUT8 = 0 ' be sure SerOut pin is stable at zero PAUSE 1000 DOAGN: SEROUT 8, BaudMode, 10, [noparse][[/noparse]"P0", "W0cc", "S044"] 'perform temp meas ' note strong pullup PAUSE 1100 ' wait for conversion to complete SEROUT 8, BaudMode, 10, [noparse][[/noparse]"P0", "W0cc", "W0be"] ' send temperature data SEROUT 8, BaudMode, 10, [noparse][[/noparse]"R0"] ' fetch data SERIN 7, Baudmode, 1500, TimeOut, [noparse][[/noparse]DEC X.LOWBYTE] PAUSE 100 SEROUT 8, BaudMode, 10, [noparse][[/noparse]"R0"] ' fetch data SERIN 7, Baudmode, 1500, TimeOut, [noparse][[/noparse]DEC X.HIGHBYTE] PAUSE 100 ' now do the calculations SignBit = X / 256 / 128 IF SignBit = 1 THEN ' its negative X = X ^ $ffff + 1 ' take the two's comp ENDIF ' multiply by 6.25 - This is 100 * Tc Y = X / 4 ' 0.25 X = X * 6 + Y Whole = X / 100 Fract = X // 100 IF SignBit = 1 THEN DEBUG "-", DEC Whole, ".", DEC2 Fract, CR ELSE DEBUG DEC Whole, ".", DEC2 Fract, CR ENDIF PAUSE 3000 ' wait 3 secs LOOPTimeOut: DEBUG "Timeout Error", CR GOTO AGN

phil kenny · 2007-12-15 08:11

Hello Sassy,

Your initial code has problems below 32 deg. F and can be fixed by
adding the following snippet:

IF SignBit = 1 THEN ' its negative
X = X ^ $ffff + 1 ' take the two's comp
ENDIF

As well as changing the name of the raw temperature value read
from the DS18B20 from X to Temp_Raw

Change the code to read:

=====================================

'Now do the Calculations

' Note that the original raw temperature is stored in a variable named
' Temp_Raw and X is a completely different variable

SignBit = Temp_Raw/ 256 / 128

IF SignBit = 1 THEN ' its negative
Temp_Raw = Temp_Raw ^ $ffff + 1 ' take the two's comp to make it positive
ENDIF

'Multiply by 11.25 - This is 100 * Tf
Y = Temp_Raw / 4 '0.25
X = Temp_Raw * 11 + Y

IF SignBit = 1 THEN ' its negative
X = X ^ $ffff + 1 ' take the two's comp to make X negative, if needed
ENDIF

x = x + 3200 'Add 32 degrees ************
Whole = X / 100
Fract = X // 100

====================================

and it should work down to 0 degrees F.

phil kenny

Post Edited (phil kenny) : 12/15/2007 8:47:48 AM GMT

phil kenny · 2007-12-16 20:15

Hello Sassy,

Attached is code that works over the full range from -55 C to +124 C.

It has been tested using the values shown in Table 2 of the DS18B20
data sheet.

The code can be simplified, but I felt it would be easier to understand
the logic if it was more verbose.

Hope this helps.

phil kenny

Post Edited (phil kenny) : 12/16/2007 8:42:37 PM GMT

Tracy Allen · 2007-12-17 17:57

Phil and Sassy,

Here is a routine that reads the DS18B20 and calculates degC and degF in two lines. Note that the sign of each is defined as an alias to bit15 in each variable.

 ' ----------------------------------------------------------------------------------------------
' {$STAMP BS2pe}
' {$PBASIC 2.5}
' Tracy Allen, EME Systems
' DS18B20 (12 bit) program displays temperature, -55 to +125 Celsius +/- 0.1 degree
' For a single DS18B20 on the one-wire buss--the skip ROM command is used here.
' If more than one is on the buss, then the match ROM command must be used.
' Note that this routine is not good for the older 8-bit DS1820 nor the DS18S20.
degC VAR Word
signC VAR degC.bit15   ' alias for sign bit
degF VAR Word
signF VAR degF.bit15   ' alias for sign bit
DO
  OWOUT 0,1,[noparse][[/noparse]$CC, $44]
  DO : OWIN 0,4,[noparse][[/noparse]degC] : LOOP UNTIL degC  ' wait for done
  OWOUT 0,1,[noparse][[/noparse]$CC, $BE]
  OWIN 0,2,[noparse][[/noparse]degC.byte0, degC.byte1]
  degC = -signC ^ (abs degC */ 160) + signC   ' convert to degC*10, good for -degC too.
  degF = degC + 1000 * 9 / 5 - 1800   ' convert to F using offset trick
  
  DEBUG "degC=", REP "-"\signC, DEC ABS degC/10, ".", DEC1 ABS degC,TAB
  DEBUG "degF=", REP "-"\signF, DEC ABS degF/10, ".", DEC1 ABS degF, CR
  PAUSE 1000
LOOP

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Tracy Allen
www.emesystems.com

phil kenny · 2007-12-18 17:38

Tracy,

Thanks for showing the 'Offset trick'. Always looking for ways
to reduce the code, Nice technique.

phil

Dave-W · 2007-12-18 20:06

Tracy,
I tried your code today on a DS18B20 and the program runs fine. However the temp readings I am getting are not correct. At 67 degrees F I am reading 33 degrees F. I looked over the code 20 times and I do not see why the readings are off? Everything looks correct. Do you have an idea?
Dave

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
D. A. Wreski

Tracy Allen · 2007-12-19 02:52

Sorry, I forgot to add 320 for the degF*10 conversion. It should read,

' ----------------------------------------------------------------------------------------------
' {$STAMP BS2pe}
' {$PBASIC 2.5}
' Tracy Allen, EME Systems
' DS18B20 (12 bit) program displays temperature, -55 to +125 Celsius +/- 0.1 degree
' For a single DS18B20 on the one-wire buss--the skip ROM command is used here.
' If more than one is on the buss, then the match ROM command must be used.
' Note that this routine is not good for the older 8-bit DS1820 nor the DS18S20.
degC VAR Word
signC VAR degC.bit15   ' alias for sign bit
degF VAR Word
signF VAR degF.bit15   ' alias for sign bit
DO
  OWOUT 0,1,[noparse][[/noparse]$CC, $44]
  DO : OWIN 0,4,[noparse][[/noparse]degC] : LOOP UNTIL degC  ' wait for done
  OWOUT 0,1,[noparse][[/noparse]$CC, $BE]
  OWIN 0,2,[noparse][[/noparse]degC.byte0, degC.byte1]
  degC = -signC ^ (abs degC */ 160) + signC   ' convert to degC*10, good for -degC too.
  degF = degC + 1000 * 9 / 5 - 1800 + 320 ' convert to degF*10 using offset trick <---------
  
  DEBUG "degC=", REP "-"\signC, DEC ABS degC/10, ".", DEC1 ABS degC,TAB
  DEBUG "degF=", REP "-"\signF, DEC ABS degF/10, ".", DEC1 ABS degF, CR
  PAUSE 1000
LOOP

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Tracy Allen
www.emesystems.com

plankton · 2009-07-23 08:19

All,

Can you use the DS18B20 in 'power steal mode' where pins 1 and 3 are tied to ground?

Thanks

Scott

Tracy Allen · 2009-07-23 15:51

Scott,

The Stamp does not have the capability to switch over to the "strong pullup" needed during the conversion. This came up in another thread recently. PhiPi suggested an word-around for a two-wire implementation, where a diode and capacitor local at each node would store the necessary power to operate the sensor in 3-wire mode.

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Tracy Allen
www.emesystems.com

plankton · 2009-07-27 03:04

Tracy - I tried using the DS18B20 in 'power steal mode' but just wasn't stable no matter how much time I gave the sensor to 'recharge'. I ended up running 4-wire phone cable so I could provide +5VDC and that solved the problem. Your logic works perfectly and now I can read temp from two sensors.

Thanks as always for you help.

Scott

Yoshti · 2010-03-18 15:43

Hi all,
I got the DS18b20 working. Some site does not show the pull-up resister. Finally in the OWIN help file, it shows I must use
the pull-up 4.7k for the 1 wire. Yes got it working !

Now, I'll be using many 18B20, and trying to get the ID off of it.
I issue a OWOUT 0,1,[noparse][[/noparse]$33]
then OWIN 0,2,[noparse][[/noparse]serial]
and all i get is a (
hum... serial is defined as a var Word.
I'm using the BS2px ...

I'm totally lost here...

Sorry to bring that old thread.. but I'm way out of my league here...

Any help ..pretty please!
Cheers
Yosh

Yoshti · 2010-03-19 14:22

Hi all,
Ok found the solution! Not very clear but all sorted out!

On this thread: http://forums.parallax.com/forums/default.aspx?f=5&m=89924

A fairly well explained (not for a noob and old fart like me) post , that is giving the code for it.

For the noob , the file owsearch2 is only a part of what you need.

If you read carefully, you have to get the code on the nuts and volts provided in the same thread.

Be carefull ! for which BS you use, so modify your directive accordingly.
Mine had to be set to BS2px and pbasic 2.5 ..and the file extension was change to .BPX .
So, to help, my searchdemo.pbx directive was set to:
STAMP BS2px, OWSEARCH2.BPX,DSNAMES.BPX
PBASIC 2.5

So it works... finally
Just helping anyone who might be getting frustrated...

Cheers
Yosh

Help with DS18B20 Code

Comments