Trouble with LCD 2x8 and sequential display of values

[fratello]

Hello !
I try to build one volt/termometer with 16F684 and 2x8 characters display. I wrote the code, all works ...fine, the "IN" temperature is shown for 8 seconds, the "OUT" temperature for next 8 seconds, and so on, and so on (the voltage is on second line permanent)....
BUT : sometimes, the value of temperature "jump" to "0.0 'C", especially when the temperature decreases ?! I really don't understand why . I made many changes in "pause", in "Define LCD_COMMANDUS 2000" and "Define LCD_DATAUS 50" , I added/removed " WaitLoop1: While not DQ1 : Wend" , but without results...
Any clue ? Thanks in advance !
This is "the big part" of my code :

Main :
Gosub Get_Vbatt                           ' make a new measure
            TmpW = Vbatt * Vfs                    ' AD * 20480
          TmpW = Div32 1024                     '(AD * 20480) / 1024       
Gosub char_batt 
        LcdOut $FE, $c0, symb ," ", dec TmpW dig 4,dec TmpW dig 3,",",dec TmpW dig 2, " V" 

Gosub StartTimer
While seconds =< 8
Part1:
    ' Start temp.conv.Sensor1
     OWOut DQ1, 1, [$CC, $44] 
     OWOut DQ1, 1, [$CC, $BE]
       OWIn  DQ1, 2, [temperature1.byte0, temperature1.byte1]  
    
        If Temperature1.15 then       
              Temperature1= ~Temperature1 +1
              Twist1 = 1
        Endif
 
    Dummy1 = 625 * Temperature1
    TempC1 = DIV32 10 
    TempC1 = (Temperature1 & $7FF) >> 4
    Float1 = ((Temperature1.Lowbyte & $0F ) * 25 )>>2
    Temperature1 = TempC1*100 + Float1

        If Twist1 then
                V1= 10000 - Temperature1                 
              Twist1 = 0
         else
              V1= 10000 + Temperature1
        EndIf

        If V1 >= 10000 then                           
              Temperature1=V1-10000                   
         else                                   
              Temperature1=10000-V1                    
        EndIf

    GoSub SelectSign
           If (temperature1/100) =>10 then
                LcdOut $FE, $80, "I:", Sign1, DEC (Temperature1 / 100), ".", DEC Temperature1 dig 1, 0
            else
                LcdOut $FE, $80, "I:", Sign1, $14, DEC (Temperature1 / 100), ".", DEC Temperature1 dig 1, 0
            Endif
      Pause 500
Wend
'===================================================================================================================
While seconds >= 9 and seconds =< 17 
Part2 :    
      ' Start temp.conv.Sensor1
     OWOut DQ2, 1, [$CC, $44] 
     OWOut DQ2, 1, [$CC, $BE]
      OWIn  DQ2, 2, [temperature2.byte0, temperature2.byte1]  

        If Temperature2.15 then       
          Temperature2= ~Temperature2 +1
          Twist2 = 1
        Endif
 
    Dummy2 = 625 * Temperature2
    TempC2 = DIV32 10 
    TempC2 = (Temperature2 & $7FF) >> 4
    Float2 = ((Temperature2.Lowbyte & $0F ) * 25 )>>2
    Temperature2 = TempC2*100 + Float2

        If Twist2 then
              V2= 10000 - Temperature2               
              Twist2 = 0
         else
              V2= 10000 + Temperature2
        EndIf

        If V2 >= 10000 then                           
              Temperature2=V2-10000                   
         else                                   
              Temperature2=10000-V2                   
        EndIf

    GoSub SelectSign
            If (temperature2/100) =>10 then
                LcdOut $FE, $80, "O:", Sign2, DEC (Temperature2 / 100), ".", DEC Temperature2 dig 1, 0
            else
                LcdOut $FE, $80, "O:", Sign2, $14, DEC (Temperature2 / 100), ".", DEC Temperature2 dig 1, 0
            Endif
      Pause 500
Wend
Gosub ResetTime
Goto Main

I have in code "include elapsed.bas" of course...The internal osc is set to 4 MHz.

[fratello]

Even in Proteus I see this trouble, if "Out" temperature decreases verry fast ...
(Just remove final extension of files)

[fratello]

...or another way to display sequential values of temperature(s), while - on second line- display the voltage ?!
Have someone another ideea ? Thanks !

[Darrel Taylor]

... BUT : sometimes, the value of temperature "jump" to "0.0 'C", ...
I have in code "include elapsed.bas" ...

1-Wire and interrupts don't get along very well together.
1-Wire has some pretty strict timing requirements, and interrupts like to mess that up.

You can get good readings, but you have to plan on bad data occasionally.
Which means verifying the CRC, and checking for all 0's in the packet. The CRC will pass (incorrectly) with all 0's
You can use the CRC routines from Tom Estes ... http://www.picbasic.co.uk/forum/showthread.php?t=1672
If the CRC fails, just go back and read the temperature again, no need to do another conversion.

That of course means you need to read the sensor as a Packet, instead of individual variables.

You also need to wait for the conversion to complete, either by PAUSE'ING the required amount of time, or polling the busy bit.
Currently, you are not waiting at all after a conversion command.

[fratello]

Thank You for support !
...it's another way to do this ?
I don't think I have enough space for adding something like CRC routines in my code (using 16F684)...

[ScaleRobotics]

How about just throw away values that are outside of expected ranges? Like take a running average, and if the temp is way off, disregard it. That way, it can still be 0 deg C, but only if its close to the average temp.

[fratello]

Thank you all for support !
Since the "timming" it's not so important , I made this change :

    ' Start temp.conv.Sensor1      
OWOut DQ1, 1, [$CC, $44]       
OWOut DQ1, 1, [$CC, $BE]      
OWIn  DQ1, 2, [temperature1.byte0, temperature1.byte1]        
Pause 800 ; because DS18B20 need 750 ms for conversion         
If Temperature1.15 then                      
Temperature1= ~Temperature1 +1               
Twist1 = 1         
Endif
...

...and the display works fine now...despite the decrease of speed in display the changes of temperatures.

[fratello]

I rushed... still have, from time to time, "0.0 'c" on display, ONLY for sensor on DQ2 (out sensor) .... ....

[gadelhas]

I rushed... still have, from time to time, "0.0 'c" on display, ONLY for sensor on DQ2 (out sensor) .... ....

Why not you poll the busy bit, instead of the Pause 800 statment?

I don't know your application, but you can also disable interrupts before the 1-wire stuff, and then enable them again.

[fratello]

I don't know your application, but you can also disable interrupts before the 1-wire stuff, and then enable them again.

Thanks for help ! How can I make this ? The most part of code it's in post #1...