DS18S20 displays wrong temperatures

I am a newbie to this forum.
I have DS18S20 displaying problem. My system uses LCD (16x2, Hitachi 44780 controller-based SC1602BSLB), PBP v.2.45 and 16F877 with 4MHz ceralock. At a room temp. of 19 degrees C (by mercury thermometer), for example, I get 155.18 degrees C on LCD. If I touch DS18S20 chip with my fingers, it gradually rises up to about 220.xx degrees C. If the chip is heated by soldering iron, when the display reaches to somewhere around 650.xx degrees C, it suddenly drops to 0.xx degrees C and begins to rise again. I cannot solve this wrong-temperature displaying problem. I need your help. Pin connections and the codes I used are as follows. Thank you.

'Pin 1 - Vdd (+5V)
'Pin 2 - Vss (GND)
'Pin 3 - Vo
'Pin 4 - RS to RD2 (PIC)
'Pin 5 - R/W (GND)
'Pin 6 - E to RD3 (PIC)
'Pin 11 - RD4 (PIC)
'Pin 12 - RD5 (PIC)
'Pin 13 - RD6 (PIC)
'Pin 14 - RD7 (PIC)
'DS18S20 - DQ pin to RC2(PIC), DQ pin to Vdd pin via 4.7 k r, GND pin to GND

Define LCD_DREG PORTD
Define LCD_DBIT 4
Define LCD_RSREG PORTD
Define LCD_RSBIT 2
Define LCD_EREG PORTD
Define LCD_EBIT 3
Define LCD_BITS 4
Define LCD_LINES 2

DQ var PORTC.2
temperature Var Word
count_remain Var Byte
count_per_c Var Byte

ADCON1 = 7
pause 100

Main: OWOut DQ,1,[$CC,$44]
Waitloop: OWIn DQ,4,[count_remain]
If count_remain = 0 Then Waitloop
OWOut DQ,1,[$CC,$BE]
OWIn DQ,0,[temperature.LOWBYTE,temperature.HIGHBYTE,Skip 4,count_remain,count_per_c]

temperature = (((temperature >> 1) * 100) - 25) + (((count_per_c - count_remain) * 100)/count_per_c)
Lcdout $fe,1,DEC (temperature/100),".",DEC2 temperature," C"

Pause 1000
Goto Main
End


'Shozo Kanamori (Tokyo)

My temperature sensor provided by Maxim was actually DS18B20 instead of DS18S20. I found this by carefully observing the sensor's surface with a magnifying glass. I never had doubts about this. The resemblance between "B" and "S" made me spend many hours of frustrating time. Sorry for the viewers.

Shozo Kanamori
It's not easy for hobbyists to get DS18S20 here in Tokyo.

Shozo,
here I found a well done prg. for 18B20 that maybe can help you.
http://www.rentron.com/PicBasic/one-wire3.htm

bye

Hi Lotondo,

The article you introduced me seems to be very helpful. I have browsed a lot of webpages but never come across this article before. I will soon start my experiment using DS18B20.

Thank you.

Shozo Kanamori

Nice to read that my link maybe helpful.
By the way, I have trouble using ds18S20 with temperature below 0° celsius
if you see some code regarding how to use it, pls link it to me.
Thanks
Bye

Darell Taylor has some very nice temp conversion routines here http://www.pbpgroup.com/ you might also find very useful.

Thanks Bruce!

I was talking with someone else off forum that had problems using the conversion routines with a DS1820 and negative temperatures, so I came up with this.

Code:

---

Sign  VAR  BIT
TempC VAR  WORD

Sign = temperature.15
TempC = ABS(temperature)
TempC =(TempC>>1)*10 + (TempC.0 * 5)
IF Sign then TempC = 0 - TempC

---

He said it worked, but I haven't tried it myself.

HTH,
  Darrel

I will post code and you will see where is (I will note it) added change which resolve problem and working 100%
This example was coded for PIC16F84A for my job.

Code:

---


Define        LCD_DREG        PORTB
Define        LCD_DBIT        4
Define        LCD_RSREG        PORTB
Define        LCD_RSBIT        2
Define        LCD_EREG        PORTB
Define        LCD_EBIT        3

TempR        var word    'DS1820 read Temperature
TempNeg      var byte    'temperature sign -/+

'*****DS1820 VARS AND SETTINGS*******
count_remain var byte  'DS1820 coumter of remain bits
count_per_c  var byte  'DS1820 counter per C bits
symbol DQ = PortA.3    'OneWire data pin
'**********************************

TrisA        =        %11111
PortA = 0
TrisB        =        %00000000
PortB = 0

Main:
  gosub Read_Temp
  if TempR=$FFFF then Error
  gosub Disp_Temp
  pause 100
goto Main

'******DS1820 READING******
Read_Temp:
  OWOut DQ, 1, [$CC, $44]                ' Start temperature conversion
  waitloop:
  OWIn DQ, 4, [count_remain]                  ' Check for still busy converting
    If count_remain = 0 Then waitloop
  OWOut DQ, 1, [$CC, $BE]                  ' Read the temperature
  OWIn DQ, 0, [TempR.LowByte, TempR.HighByte, Skip 4, count_remain, count_per_c]

if TempR = $FFFF then return
    if (TempR.HighByte = $FF) and (TempR.LowByte <> 0) then
      TempNeg = "-"
      TempR = TempR ^ $FFFF
      TempR = ((TempR >> 1)*100) - 25 + ((count_per_c + count_remain) * 100) / count_per_c     
      else
    if (TempR.HighByte < $FF) and (TempR.LowByte <> 0) then 
      TempNeg = "+"
      TempR = ((TempR >> 1)*100) - 25 + ((count_per_c - count_remain) * 100) / count_per_c
      else
'************************************************
      TempR=$0000    ' THIS IS ONLY NEED TO DEFINE !!!
'************************************************
    endif
endif
return

Disp_Temp:
        Lcdout $fe, 1, "Temperature: " TempNeg, DEC (TempR / 100),".", DEC2 TempR, 223, "C "
return

Error:
  Lcdout $fe, 1, "!!!ERROR!!!", $fe, $C0, "Reading Temp."
goto Main
end

---

Now I think that this thread (I am not find any fresh thread with solved problem) was solved :)
This code measure temperature with extended resolution (DEC2).


Regards.