DS18B20 - Whole number only

[Gordon23]

Hi,

I have used the DS18B20 example project, with a PICF18855, i have not changed the code, or the driver ds18b20. (only included my header file to the top of the main.c file)

I have connected my PIC to a terminal program via my UART lead.

I have the following header for my device:-

#include <16F18855.h>
#use delay(internal=12MHz)
#use rs232(baud=9600,parity=N,xmit=PIN_C6,rcv=PIN_C7,bits=8,stream=PORT1,FORCE_SW)

I found i had to use 12mhz to make it work at all -

It is working, but i can only see whole results, i.e. temp=19C - it does vary when touch etc.

Am i doing something wron with the output?

Any pointers would be grateful.

Thanks.

[PrinceNai]

Hi,

the code should be so short you could post it complete. One question: why are you using software UART?

[temtronic]

comments..

'high' numbered PIC... does it have PPS ?
Peripheral Pin Select requires you to 'map' them before using them AND not all pins can be mapped to all perhipherals.

whole number only could be the 'print format' you're using. Do you send to a local LCD module or via RS232 to a PC running a terminal program ?

One Wire requires a certain speed to run properly.

As others have said, need to see your 'short' program to debug.
I've used that temp sensor a lot so I know it works with the PIC18F46k22, and others.

[Gordon23]

Is it OK to publish the CCS code?

I have used the digital therm example, and the ds18b20 driver, i have not modified them in any way. (just included my header).

I am using a terminal program, i must have the pin setup as i am received data, looks like i am seeing just one byte, not the remainder.

So i think i am not formatting or sending this correctly, the CCS example is for the e3 mini.

Thanks

[newguy]

Don't post any CCS header files.

Publish what you have written. A simple #include <ccs file> will suffice if you have not modified the CCS file.

Be sure to include your specific compiler version.

[Ttelmah]

You understand that you need to cast the returned value before you
divide it to give a fractional result.
So you have an integer value from the sensor as temperature *16.
If you are making a floating point degrees value from this you need to use:

degrees = temp/16.0;

or

degrees = (float)temp/16;

If instead you code as:

degrees = temp/16;

This will use _integer_ division, so you will only get integer degrees in
the result. Degrees must be a float.

[Gordon23]

Thank you Ttelmah.

This worked perfect, i think i perhaps picked the worng project to get started with, but i will take some time trying to undertand.

Thanks

[PrinceNai]

It's quite easy. You declare your Temp variable as int16. You read the sensor and get a 40 in Temp. Now you divide Temp/16 and get a 2. This is integer division that doesn't care about fractions, only whole numbers. You could declare Temp as a float at the start or use casting as Mr. Ttelmah wrote. In that case Temp/16 will give you a 2.5, which is the correct result or better, the result you are looking for.

[temtronic]

FWIW, found this 'somewhere' on this PC....

stuff I can kinda recall( it's been YEARS...)
reading is changed into *C scaled integers...
that's converted to *F ,cause I like *F...
LCD module display raw DStemp sensor bits
as well as temperature in *C and *F
I used 1 temp sensor per I/O pin

dsbits is the 16 bits from the DS temp sensor..

void display2() {
dscopy=dsbits; //save a copy of original dsbits
if(dsbits&0x8000)
{
dscopy=dsbits;
dsbits=~dsbits+1;
dstemp=dsbits;
dstemp =(dstemp>>4)& 0x00FF; //-ve *C rdg
}
else
{
dstemp=dsbits;
dstemp=(dstemp>>4) & 0x00FF; //+ve *C rdg
}
// scaled integer temperature
s=dstemp; //*C temp
s=s*10000; //scaled *C temp
//add on fractional part of raw temperature
if(dsbits&0x0001) s=s+625; //add fractions
if(dsbits&0x0002) s=s+1250; //as
if(dsbits&0x0004) s=s+2500; //required
if(dsbits&0x0008) s=s+5000; //1255000 = 125.500*C

sf=s;
sf=sf*9;
sf=sf/5;

if(dscopy&0x8000) {
sf=320000-sf;
if(sf<1)np='-';
}
else {
sf=320000+sf;
np=' ';
}
lcd_gotoxy(1,1);
printf(lcd_putc,"DS %4lx",dsbits);
lcd_gotoxy(1,2);
printf(lcd_putc,"current");
lcd_gotoxy(1,3);
printf(lcd_putc,"%c",np);
lcd_gotoxy(2,3);
printf(lcd_putc,"%7.4w",sf);