Iwould be most grateful if your experts on using the C18 compiler could give me a pointer as to what I am doing wrong. To become familiar I started a simple thermometer project:- NTC thermistor --> 18F2520 --> HD44780.
After getting the chain debugged and producing the code to convert the AN0 input voltage , mid range 2.5V = 10000 ohm, all was well including the needed routines to get the TºC onto the LCD.
The above was bare bones but working nicely producing a new LCD dispay of TºC every second.
Next step was to become a little more sofhisticated,
At the beginning of the tcalc function I put in an out of range test. If as I had initially decided, the application was going to measure water temperature. Then Rntc greater than 28000 would be ice, (out of range above ) At the other end of valid values <1900 is getting almost to steam. The routine I was calling to give an error message was being igmored.
Here is the tcalc code to change Rntc into a temperature TºC
/**************************************************
Start tcalc
***************************************************/
void tcalc(unsigned char value) // does Rntc to T maths
{
// start read AN0 for ADRESH ADRESL
ADCON0 = 0x03;
while( ADCON0 == 0x03);// loop A/D 11 bits
// notes at end explain 11bit convert in 5 us
Delay10TCYx(20); // +20us saftey margin
ADRESH =0x02; //Dummy we use 512 as test value
ADRESL =0x00;// Dummy 0x200 = d512
Vin= ADRESH*256+ADRESL;
Rntc = (1024.0*Rref)/Vin -Rref;
// Rntc = 29000;//DUMMY test 2hi
/***********************************************
Rntc MUST be valid (in range) test above/below
***********************************************/
if ( Rntc>28000) // Rntc too high
{
Rntc_out; //jump to Show HIGH error message
}
dly1sec;
if (Rntc<1900) // Rntc too low
{
Rntc_out; //jump to Show LOW error message
}
/***********************************************
Pairing Rntc value, with T equation coefficients
***********************************************/
if (Rntc>14706) //case 1
{
a = 19.67,b = -1136.15, c = 27335.25 ;
goto Trange_1thru5 ;
}
if (Rntc>8310.8) //case 2
{
a = 9.228,b = -840.85, c =25236.82 ;
goto Trange_1thru5 ;
}
if (Rntc>4910.6) //case 3
{
a = 4.554,b =-567.886, c = 21246.2 ;
goto Trange_1thru5 ;
}
if (Rntc>3019.7) //case 4
{
a = 2.358,b = -373.486, c = 16941.29 ;
goto Trange_1thru5 ;
}
if (Rntc>1924.6) //case 5
{
a = 1.275,b = -245.047, c = 13131.885 ;
goto Trange_1thru5 ;
}
Trange_1thru5:
c= c-Rntc;
T = (-b - sqrt(-b*-b -4*a*c))/(2*a);
/* Quadratic T result chosen has to be lowest */
}
/******************************************************
END tcalc
*******************************************************/
The called routine 'Rntc_out' is as follows
/*******************************************************
****** Start Rntc_outofrange ******
********************************************************/
void Rntc_out (unsigned char value)
{
lcdcmd(0x80);//move to top line of LCD
// RntcHL =Rntc;
if (Rntc<1900) //Rntc too low
{
lcddata('R');
lcddata('n');
lcddata('t');
lcddata('c');
lcddata(' ');
lcddata('t');
lcddata('o');
lcddata('o');
lcddata(' ');
lcddata('L');
lcddata('o');
lcddata('w');
lcdcmd(0xC0);//Bottom line of LCD
T = Rntc;
float_to_char;
dly1sec;
dly1sec;
dly1sec;
dly1sec;
dly1sec;// Rntc low on screen 5 seconds
}
if ( Rntc>27500) // Rntc too high
{
lcddata('R');
lcddata('n');
lcddata('t');
lcddata('c');
lcddata(' ');
lcddata('t');
lcddata('o');
lcddata('o');
lcddata(' ');
lcddata('H');
lcddata('i');
lcddata('g');
lcddata('h');
lcdcmd(0xC0);//Bottom line of LCD
T = Rntc;
float_to_char;
dly1sec;
dly1sec;
dly1sec;
dly1sec;
dly1sec; // Rntc high on screen 5 seconds */
}
}
/*******************************************************
****** End Rntc_outofrange ******
********************************************************/
Basically my question is when testing for out of range Rntc. The code is skipped as if it were not there.
PS If I put the Rntc module's code as a Label : and goto the code, then yes the test for out of range is not ignored and the condition can be serviced.
Of course the 'goto' ploy has a little problem. The outof range reading means that after a few seconds, the thermistor has to be read again. meaning another goto to tcalc. meaning calling itself. C18 doesn't seem to like this.
I would be very happy if some kind soul could point out the error of my code at least in general.
