Down convert 10 bit to 8 bit

[zulkifliaziz]

Hi all,

I'm having a problem to understand how to convert 10 bit data to become 8 bit.

First of all, what i want to implement is to use an ADC from analog data (0-5V).

So, from my understanding,

10 bit data = 1024 (max)

in this case, if 5V=1024 and if 2.5V=512

But, to communicate with rs232, we have to use 8 bit = 1 byte each data being sent plus start bit and stop bit.

char temp_res;
char temp_text[7];

void main() 
{
  Uart1_Init(9600);
  ADCON1 = 0x80;
  TRISA  = 0xFF;
  TRISB = 0;
  PORTB = 0B00000000;
  for(;;)
     {
        temp_res = ADC_Read(1);
        if(temp_res>125)
           {
               ByteToStr(temp_res,temp_text);
               PORTB=0B00000001;
               Delay_ms(100);
               PORTB=0B00000000;
               Delay_ms(100);
               Uart1_Write(temp_text);
               Delay_ms(100);
           }
       }
 }

From the code above, do u see any wrong doing. pls help. What i want to know is that, why the number for this chattared keeps alway changing itself.

 

[Tahmid]

Hi,
Firstly 10 bit data = 1023 max (0-1023, that's 1024 numbers)
5v = 1023

In your code, you use the function ByteToStr, but temp_res is not a byte.
So, have another variable as "temp_res_byte" and convert "temp_res" to byte.
Try this:

char temp_res;
char temp_text[7];
unsigned char temp_res_byte;

void main() 
{
  Uart1_Init(9600);
  ADCON1 = 0x80;
  TRISA  = 0xFF;
  TRISB = 0;
  PORTB = 0B00000000;
  for(;;)
     {
        temp_res = ADC_Read(1) >> 2;
        temp_res_byte = temp_res;
        if(temp_res>125)     -------------------------------------->  //Why is this here?
           {
               ByteToStr(temp_res_byte,temp_text);
               PORTB=0B00000001;
               Delay_ms(100);
               PORTB=0B00000000;
               Delay_ms(100);
               Uart1_Write(temp_text);
               Delay_ms(100);
           }
       }
 }

To convert 10-bit to 8-bit, you need to divide by 4, ie >>2 (bitshift 2 to the right, which essentially means the same as divide by 4).

Hope this helps.
Tahmid.

 

[zulkifliaziz]

it doesn't work. Infact, that the character doesn't change when i give different voltages for the adc. this is what i got from the usart terminal of the microC