Value of temperature

[Charlie]

You did not post enough code that we can answer your question. Post all of your code.

[cobuccit]

You did not post enough code that we can answer your question. Post all of your code.

 



define osc 4
adcon1.7=1
ANSEL = 0001 'Disable Inputs Tranne AN0
ADCON1 = 001110 
OSCCON = 100000 'Internal RC set to 4MHZ
TRISA =  000001 ' impostazioni INP/OUT
TRISB =  000000 ' delle porte
'----------------------------------------------------
DEFINE LCD_DREG PORTB       'Porta B DATA OUT 
DEFINE LCD_DBIT 4           '0 --> Bit 0-3 : 4 --> Bit 4-7 
DEFINE LCD_RSREG PORTB      'LCD register select port - Porta B --> RS
DEFINE LCD_RSBIT 2          'LCD register select bit  - Pin RS B2
DEFINE LCD_EREG PORTB       'LCD enable port - Porta B --> EN
DEFINE LCD_EBIT 3           'LCD enable bit - Pin EN B3DEFINE LCD_BITS 4           'LCD bus size 4 or 8 
DEFINE LCD_LINES 2          'Number lines on LCD DEFINE LCD_COMMANDUS 2000   'Command delay time in us 
DEFINE LCD_DATAUS 50        'Data delay time in us


Rele   VAR    PORTA.6     '                  Pin 15
'--------------------------------------------------------------
'---------Define ADCin Parameters   
DEFINE ADC_BITS 10      'set number of bits in result
DEFINE ADC_CLOCK 3      'set clock source (3=rc)
DEFINE ADC_SAMPLEUS 50  'Set sampling time in uS




'    RAM Assignments and Variables
'=========================================================================== 
temp var word
temperature var word
samples var word
sample VAR BYTE
quanta con 1250
Tmax VAR byte
Tmin VAR byte
'===========================================================================
Tmin=16
Tmax=30
 
START:
Lcdout $FE, 1


low rele


main:   
sample = 1
samples= 0
FOR sample = 1 TO 20 'Take 20 samples
ADCIN 0, temp 'Read AN0 into temp variable
samples = samples + temp
PAUSE 50 ' Wait 1/4 seconds per reading
NEXT sample
temp = samples/20 'Average over 20 samples (Every 5 seconds)
temperature= temp */ quanta


if temp > 675 then high rele  'Instead 675 write the correct RAW number for 30degC 
if temp < 675 then low rele   'Instead 675 write the correct RAW number for 30degC 


LCDOUT $FE, 2 ' ritorna al primo carattere
lcdout $FE, 2, "Temp ",dec2 (temperature/10),".", dec1 (temperature/10),"C"
'lcdout $FE, $C0, "Tmin ",#Tmin, " Tmax ",#Tmax            FOR NORMAL OPERATION UNCOMMENT LINE 
lcdout $FE, $C0, "RAW:",dec temp 'this show the ADC value  FOR NORMAL OPERATION COMMENT OR DELETE THIS LINE
'lcdout $FE, $C0, "RAW:",dec temperature

'When the display show 30,0 degC look at the RAW number on LCD and rewrite it in lines: if temp > 675 then high rele
'and if temp < 675 then low rele . 


goto main

[Dave]

I believe you are going wrong by not subtracting the zero degree C. offset before you calculated the final value of quanta. Here is what I calculate:

0 degrees C. = 273.15 degrees K.
273.15 degrees K. x .01 volts = 2.7316 volts @ 0 degrees C.
5 volts / 1023 counts = .004887586 volts per count
2.7315 volts / .004887586 volts per count = 588.86484 counts
588.86484 raw counts = 0 degrees C. = 273.15 degrees K.

After subtracting the 588.86 counts from the raw reading, you end up with:
.01 volts per degree C. / .004887586 volts per count which equals 1 degree C.