NTC thermistor temperature sensing

**mackrackit** · - 15th January 2011, 15:52

Never trust a sim.
Try it in real life and come back.

**Acetronics2** · - 15th January 2011, 16:08

ADCIN 1,tb0
tb1=tb0-16170
tb1=tb1*tb3
tb2=Div32 634
tb0=tb2/100
tb1=tb2//100

see any difference between Tb0 value @ line 1 and Tb0 Value @ line 5 ???

really no ?

Alain

**pxidr84** · - 15th January 2011, 16:40

Originally Posted by mackrackit

Never trust a sim.
Try it in real life and come back.

In real life with the same code:

Originally Posted by Acetronics

see any difference between Tb0 value @ line 1 and Tb0 Value @ line 5 ???

really no ?

Alain

My updated code :

Code:

define OSC 20
DEFINE ADC_BITS 10
DEFINE ADC_SAMPLEUS 10
DEFINE LCD_DREG PORTC
DEFINE LCD_RSREG PORTC
DEFINE LCD_EREG PORTC
DEFINE LCD_EBIT 5 

ntc VAR WORD
tb0 VAR WORD
tb1 VAR WORD
tb2 VAR WORD

TRISA=%11111111     
ADCON1=%10000010   

PAUSE 4000

lp:

ADCIN 1,ntc
tb0=ntc
if tb0>=16170 then
tb1=tb0-16170 
ELSE 
tb0=0
ENDIF
tb1=tb1*100                                      
tb2=Div32 634
tb0=tb2/100   
tb1=tb2//100    
           
PAUSE 100

Lcdout $fe,$c0,"ITS: ",DEC (tb0 DIG 1),DEC (tb0 DIG 0),".",DEC (tb1 DIG 1),"°C"

goto lp

I was surprised because the previous code worked good.

**cncmachineguy** · - 15th January 2011, 16:46

Originally Posted by mackrackit

Never trust a sim.

But this time I think the sim is correct. I think you ment to set ADCON2, not ADCON1. ADCON 2 sets right or left justified. Default is left justified.

**pxidr84** · - 15th January 2011, 16:57

Originally Posted by cncmachineguy

But this time I think the sim is correct. I think you ment to set ADCON2, not ADCON1. ADCON 2 sets right or left justified. Default is left justified.

How do you right-justify bits?
tb0=ntc>>8?

Or there is an another command?

**cncmachineguy** · - 15th January 2011, 17:01

Originally Posted by pxidr84

How do you right-justify bits?
tb0=ntc>>8?

Or there is an another command?

Look at the datasheet for ADCON2. I feel like the setting you have for ADCON1 is really ment for ADCON2. ADCON1 only has 2 valid bits. Not the 2 you have set.

BTW, tb0=ntc>>8 will shift it 8 places. you would only need to shift 6 times. Yes this will work, but better to just set the registers up for what you want, then no un-needed code

**aratti** · - 15th January 2011, 17:07

Code:

From your code:

ADCIN 1,ntc
tb0=ntc
if tb0>=16170 then
tb1=tb0-16170 
ELSE 
tb0=0
ENDIF

Since ntc could be 0 or 1023 maximum, the condition if tb0>=16170 then is always false so tbo will be always zero and tb1 will be never setted with your required calculation tb1=tb0-16170.

Cheers

Al.

**pxidr84** · - 15th January 2011, 17:34

Originally Posted by aratti

Code:

From your code:

ADCIN 1,ntc
tb0=ntc
if tb0>=16170 then
tb1=tb0-16170 
ELSE 
tb0=0
ENDIF

Since ntc could be 0 or 1023 maximum, the condition if tb0>=16170 then is always false so tbo will be always zero and tb1 will be never setted with your required calculation tb1=tb0-16170.

Cheers

Al.

The code works for me because the value of my ADC varies from 0 to 65525 (it's a 10-bit ADC, but with bits shifted to a 16-bit value).

**Acetronics2** · - 15th January 2011, 17:43

Sorry ...

But my Easy Pic5 outputs " ITS : ...00.00°C " with all the processor settings I gave you in previous code, but 10 bits ADC ... ( Whistle and Bells ... )

I also asked for printing ntc Value ...

comprised between 0 and 1023 ...

try this :

ntc VAR WORD
tb0 VAR WORD
tb1 VAR WORD
tb2 VAR WORD
TRISA=%11111111

PAUSE 700
LCDOUT $fe,1

lp:
ADCIN 1,ntc
tb0 = ntc
if tb0 >= 16170 then
tb1 = tb0-16170
ELSE
tb1 = 0
ENDIF
tb1 = tb1*100
tb2 = Div32 634
tb0 = tb2/100
tb1 = tb2//100

LCDOUT $FE,2,DEC4 ntc
Lcdout $FE,$C0,"ITS: ",DEC3 tb0,".",DEC2 tb1,"°C"
goto lp

so ... take your own conclusions !!!

Alain

**pxidr84** · - 15th January 2011, 18:00

Originally Posted by Acetronics

Sorry ...

But my Easy Pic5 outputs " ITS : ...00.00°C " with all the processor settings I gave you in previous code, but 10 bits ADC ... ( Whistle and Bells ... )

I also asked for printing ntc Value ...

comprised between 0 and 1023 ...

try this :

so ... take your own conclusions !!!

Alain

Your code works, but it still show ADC values>1024... or less on my PIC (for exemple 1616 for 24,26°C)...
The temperature reading is correct.

**Acetronics2** · - 15th January 2011, 20:03

One more thing ...

The compiler doesn't like " ° " ( "Maj" + "=" ) character ...

better use

Code:

Lcdout $FE,$C0,"ITS: ",DEC3 tb0,".",DEC2 tb1, 223, "C"

where 223 ( sometimes 178 ) is supposed to be the ASCII code of " ° " ...

That said ... ADC value NEVER is > 1023 ...

from your firsts explanations ( post #1) ... I get That : ( 16F877A on EasyPic5 )

Code:

 
DEFINE ADC_BITS 10      ' Set number of bits in result
DEFINE LCD_DREG PORTB       ' Set LCD Data port
DEFINE LCD_DBIT 0           ' Set starting Data bit (0 or 4) if 4-bit bus .7
DEFINE LCD_RSREG PORTB      ' Set LCD Register Select port
DEFINE LCD_RSBIT 4          ' Set LCD Register Select bit 
DEFINE LCD_EREG PORTB       ' Set LCD Enable port
DEFINE LCD_EBIT 5           ' Set LCD Enable bit i.e, PORTE.4
DEFINE LCD_BITS 4           ' Set LCD bus size ot 4 bit Upper Nibble (4 or 8 bits)
DEFINE LCD_LINES 2         ' Set number of lines on LCD to 4 Lines
 
TRISA  = %11111111
TRISB  = 0
TRISC  = 0
 
CMCON  = 7
ADCON0 = %11000001
ADCON1 = %10000100   
 
ntc VAR WORD
tb0 VAR WORD
tb1 VAR WORD
tb2 VAR WORD
 
PAUSE 700
LCDOUT $fe,1
lp:
ADCIN 1,ntc
tb0 = ntc * 33 /92 
tb1 = tb0*721                                     
tb2 = Div32 255
tb2 = tb2 - 64
tb0 = tb2/10   
tb1 = tb2//10    
 
PAUSE 200
 
LCDOUT $FE,2,DEC4 ntc
Lcdout $FE,$C0,"ITS: ",DEC3 tb0,".",DEC1 tb1,178,"C"
goto lp

Gives me a 0 - 100°C scale for adc = 67 to 1023 ...

so, i suppose it to be " not so bad , but to confirm "
Alain

**pxidr84** · - 15th January 2011, 21:22

Originally Posted by Acetronics

One more thing ...

The compiler doesn't like " ° " ( "Maj" + "=" ) character ...

better use

Code:

Lcdout $FE,$C0,"ITS: ",DEC3 tb0,".",DEC2 tb1, 223, "C"

where 223 ( sometimes 178 ) is supposed to be the ASCII code of " ° " ...

That said ... ADC value NEVER is > 1023 ...

from your firsts explanations ( post #1) ... I get That : ( 16F877A on EasyPic5 )

Code:

 
DEFINE ADC_BITS 10      ' Set number of bits in result
DEFINE LCD_DREG PORTB       ' Set LCD Data port
DEFINE LCD_DBIT 0           ' Set starting Data bit (0 or 4) if 4-bit bus .7
DEFINE LCD_RSREG PORTB      ' Set LCD Register Select port
DEFINE LCD_RSBIT 4          ' Set LCD Register Select bit 
DEFINE LCD_EREG PORTB       ' Set LCD Enable port
DEFINE LCD_EBIT 5           ' Set LCD Enable bit i.e, PORTE.4
DEFINE LCD_BITS 4           ' Set LCD bus size ot 4 bit Upper Nibble (4 or 8 bits)
DEFINE LCD_LINES 2         ' Set number of lines on LCD to 4 Lines
 
TRISA  = %11111111
TRISB  = 0
TRISC  = 0
 
CMCON  = 7
ADCON0 = %11000001
ADCON1 = %10000100   
 
ntc VAR WORD
tb0 VAR WORD
tb1 VAR WORD
tb2 VAR WORD
 
PAUSE 700
LCDOUT $fe,1
lp:
ADCIN 1,ntc
tb0 = ntc * 33 /92 
tb1 = tb0*721                                     
tb2 = Div32 255
tb2 = tb2 - 64
tb0 = tb2/10   
tb1 = tb2//10    
 
PAUSE 200
 
LCDOUT $FE,2,DEC4 ntc
Lcdout $FE,$C0,"ITS: ",DEC3 tb0,".",DEC1 tb1,178,"C"
goto lp

Gives me a 0 - 100°C scale for adc = 67 to 1023 ...

so, i suppose it to be " not so bad , but to confirm "
Alain

Ok, my problem is largely solved, and if change my PIC, I'll be warn of ADC values. I think my PIC is a special case.
Thanks everyone.

**Acetronics2** · - 16th January 2011, 08:56

Epilog ...

for general knowledge ... a look at Microchip AN 942 may be valuable ...

Ok, my problem is largely solved

I think my PIC is a special case.

Alain

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