| View previous topic :: View next topic |
| Author |
Message |
Guest
|
| Newb to CCS compiler A2D conversion ? 0-255 <> 0-5.00V |
 Posted: Fri Dec 19, 2008 10:05 am |
 |
|
Hi, Yep I am new to PCD from CCS.
Could someone lend a hand.....?
The following code is blinking some leds and reading AN0 port of my protoboard and then sending the reading to the computer via RS-232.
Everything work so far except for the conversion....
0-255 resolution to 0-5.00 volts output.
The pot fprint to the screen yields 0.00 - 0.04
Am I on the right track?
| Code: |
#define yellowled PIN_B4
#define redled PIN_B1
#use rs232(baud=9600, xmit=PIN_C6, rcv=PIN_C7) // Preprocessor directive that includes RS232 libraries
main (){
unsigned int8 i, value, min, max;
int pot;
setup_adc_ports(AN0); //USES DEFAULT VDD,VSS REFERENCE VOLTAGES
setup_adc(ADC_CLOCK_INTERNAL); //THIS SETS UP THE ADC mode,SPEED, & SAMPLE TIME
set_adc_channel(0);
// while (TRUE){
printf(" LEDS BLINKING\n\r");
output_low (greenled);
output_low (redled);
output_low (yellowled);
delay_ms(1000);
output_high (greenled);
output_high (redled);
output_high (yellowled);
delay_ms(1000);
for (i=1;i<3;i++){
output_low (greenled);
delay_ms(100);
output_low (yellowled);
delay_ms(100);
output_low (redled);
delay_ms(100);
output_high (greenled);
delay_ms(100);
output_high (yellowled);
delay_ms(100);
output_high (redled);
delay_ms(100);
}
// }
for(i=0;i<20;i++){
output_low (greenled);
output_low (redled);
output_low (yellowled);
delay_ms(50);
output_high (greenled);
output_high (redled);
output_high (yellowled);
delay_ms(50);
}
printf(" A2D CONVERSION BEGINNING\n\r");
delay_ms(2000);
setup_adc(ADC_CLOCK_INTERNAL); // Built-in A/D setup function
set_adc_channel(0); // Built-in A/D setup function
for(i=1; i<=10; ++i) {
min=255;
max=0;
delay_ms(2); // Built-in delay function
value = read_adc(); // Built-in A/D read function
pot = (value*100)/51;
if(value<min)
min=value;
if(value>max)
max=value;
printf("\r\nMin: %u Max: %u\n\r",min,max);
printf("\r\nPot: %3.2w ",pot);
delay_ms(3000);
}
} |
|
|
 |
Guest
|
|
| Posted: Fri Dec 19, 2008 11:10 am |
|
|
Hi
In CCS int8 and int is only 8 bit, think your "pot" must be int16.
|
|
|
Guest
|
|
| Posted: Fri Dec 19, 2008 11:25 am |
|
|
Hi,
I changed the format to %Lu in printf and I changed to int16 pot;
still not working properly....
I am only seeing 0-3 volts
the min and max are working fine 0-255 when I adjust the pot so I know that pin AN0 is seeing 0 -5V.... |
|
|
Ttelmah
Guest
|
|
| Posted: Fri Dec 19, 2008 2:07 pm |
|
|
To get 10 bits from the ADC, requires two things:
int16 for the variable, and
#device ADC=10
Otherwise the default is 8bit operation.
Two more comments:
Don't use 'ADC_CLOCK_INTERNAL'. Read the data sheet. This is not recommended above 1MHz.
Then, your arithmetic will have problems. You have an int16. This can hold numbers up to 65536. You are taking the ADC value (0 to 1023), and multiplying this by 1000. This gives numbers from 0 to 102300. These _wont fit_ into an int16. You need to use an int32 value for this operation.
Best Wishes |
|
|
SherpaDoug
Joined: 07 Sep 2003
Posts: 1640
Location: Cape Cod Mass USA
|
|
| Posted: Fri Dec 19, 2008 3:12 pm |
|
|
Where are you getting this math from?
| Code: | | pot = (value*100)/51; |
If you want to turn A/D counts into voltage you want something like
volts = (counts * fullscalevolts)/fullscalecounts
or in your case
| Code: | | pot = (value*5000)/1023; |
to give an output in integer millivolts for a 10 bit A/D with a 5.000V reference.
_________________
The search for better is endless. Instead simply find very good and get the job done. |
|
|
Ttelmah
Guest
|
|
| Posted: Fri Dec 19, 2008 3:47 pm |
|
|
But will need to be:
pot = ((int32)value*5000)/1023;
to work.
Best Wishes |
|
|
|
FAQ 
Search
Register
Profile 
Log in to check your private messages 
Log in
