Please help with code for DS18B20

[fratello]

I made the great project of "Digital thermostat (080090-11)" from Elektor july_august 2008 ; unfortunate I do not have DS1820 but DS18B20. The temperature show on display is like "xxx.xx 'C" !.
I read this : "In order to convert the HEX code to a temperature value, first you need to identify if you are using a DS18S20, or DS18B20 series sensor. The code to read the temperature needs to be slightly different for the DS18B20 (and DS1822), because it returns a 12-bit temperature value (0.0625 deg precision), while the DS18S20 and DS1820 return 9-bit values (0.5 deg precision)".
I try millions different routines, but the result is verry bad...because of this section, I think :
"DisplayTemp:
If V >= 10000 then ' Above 0 C.
Temperature=V-10000
Else
Temperature=10000-V ' Below 0 C.
EndIf
LcdOut $FE, $C0, Sign, DEC (Temperature / 100), ".", DEC2 Temperature, " ",223,"C "
Return"
All the codes I try change the Temperature set and Hysteresis, and the display show the temperature (ex. 24.56'C) , but useless function of thermostat...(Set temperature = 2000.00 and Hysteresis = 200.00).
And the temperature is different (+24.67 'C) by other device (DS18B20 + PIC 12F675 + LCD Nokia = 23.1'C ; LM35DZ + mV = 23.1 'C)
It is possible to increase the accuracy of this thermometer/thermostat ?
Can somebody help me to modify the source for using DS18B20 ?
Thanks in advance !

[Acetronics2]

Hi, Fratello

I played a bit with your program ... Elektor won't be anymore what it was ... -cries-

Note you'll have to comment the Easypic5/16F877A section and uncomment the Elektor section.

This way you will be able to use the 18B20 in any resolution you like ...

And OVERALL do not ask a +/- 0.5°C precision sensor to give 1/100° C .... !!!

Alain

[fratello]

THANK YOU VERRY MUCH !!!! You make me happy ! I will try the code and I will keep You informed. Thanks again !
****** A HAPPY NEW YEAR !!!! ******
******* TO ALL !!!! *******
LE : Now is great, even still remain the 1°C difference...but "OVERALL do not ask a +/- 0.5°C precision sensor to give 1/100° C .... !!!".
Thanks again !
B.t.w : what can I use instead of DS18B20 for more accurate measurement ?

[Acetronics2]

B.t.w : what can I use instead of DS18B20 for more accurate measurement ?

Hi, Fratello

I had a look to all the sensors you can find on the market ...

The best "out of the box" accuracy ( all including ) will be roughly +/- 0.5 °C ... don't be sad !!!

going further needs multipoint CALIBRATION ... with some really expensive devices.

Note linearity is "not so bad" in our measuring range ... so, with a two points calibration ( 0 and 100°C ) , you can reach +/- 0.1 °C without too much pain.

And remember ... DS18x20 in continuous measurement mode like here, without being fixed on a heatsink, has a 1°C self heating value ... ( a look at the Datasheet will confirm !!! )

Just have a look to the values displayed from the power up ...

Alain

[Melanie]

You missed some Alain.

We have Industrial Sensors that directly return 16-bit Temperature to two Decimal Places (in the range 0.00C-100.00C).

It is however a complete waste of time... just breathing in the vicinity, or even just walking nearby create air-currents which wildly change the readings - we just end up ignoring the last digit. If you're trying to distill some moonshine for the New Year festivities, you're not really bothered in monitoring the temperature to hundredths of a degree.

[Acetronics2]

Hi, Mel

Happy to read from you !!!

Of course, those sensors exist ... ( you have forgotten to give us the price ... lol ), but are totally out of our Hobbiysts galaxy ...

Have a Happy new Year

Regards
Alain

[mvs_sarma]

Hi, Fratello

I played a bit with your program ... Elektor won't be anymore what it was ... -cries-

Note you'll have to comment the Easypic5/16F877A section and uncomment the Elektor section.

This way you will be able to use the 18B20 in any resolution you like ...

And OVERALL do not ask a +/- 0.5°C precision sensor to give 1/100° C .... !!!

Alain

But DS18B20 is capable of giving a better resolution??

[Ioannis]

Its resolution (its step in other words) is 0.0625 but its accuracy is +/-0.5C

Ioannis

[lew247]

Hi, Fratello

I played a bit with your program ... Elektor won't be anymore what it was ... -cries-

Note you'll have to comment the Easypic5/16F877A section and uncomment the Elektor section.

This way you will be able to use the 18B20 in any resolution you like ...

And OVERALL do not ask a +/- 0.5°C precision sensor to give 1/100° C .... !!!

Alain

I've been playing with this all day today and it's a great piece of code.
I used this as I have an easypic 6*

I have one problem/question that perhaps someone could answer please

When I program the pic, the sisplay shows * at the end of the 1st line even when no buttons are or have been pressed, I thought the * was only to show a button had been pressed?

Also if I cycle through the button presses, ie set temp and set hysteresis they both work fine
however when I press the button again to show the actual temp that also works. but it never seems to update UNLESS I hold the button in, then it updates continually

I've been trying to get it to update at a regular interval or any interval but it just wont, am I doing something wrong or does it never update the temp?

[Acetronics2]

Hi,

That looks no pullups - or a Pulldown ! - on PORTA.0 input ... the " * " only appears when Porta.0 is tied to ground.

Everything fine here ...

Alain

[lew247]

Hi,

That looks no pullups - or a Pulldown ! - on PORTA.0 input ... the " * " only appears when Porta.0 is tied to ground.

Everything fine here ...

Alain

I thought that might be the problem, but where would I put
high portA.0

If I put it before the mainloop it displays the temperature all the time,
if I put it at the end of mainloop then it still displays the * and stays on set temperature.

I can't figure out where to put it, must be easy but I just cant see it.

[Acetronics2]

I thought that might be the problem, but where would I put
high portA.0

If I put it before the mainloop it displays the temperature all the time,
if I put it at the end of mainloop then it still displays the * and stays on set temperature.

I can't figure out where to put it, must be easy but I just cant see it.

May be you could place The pullup resistorS ( 3 x 47-100k ) between Porta.0,1 and 2 and VCC ...

No need to place it inside the Pic ... that won't work !

Alain