ADC to LCD charater conversion concept

[Sahil_khan]

Dear Guys

I am new to PIC Microcontroller and just started working on an example i.e. to read ADC value and convert it to ASCI and then display on LCD. I am using mikroC compiler.

Can some body explain what does the following code do ?

unsigned char ch;
unsigned int adc_rd;
char *text;
long tlong;

tlong = (long)adc_rd * 5000; // covert adc reading to milivolts
tlong = tlong / 1023; // 0..1023 -> 0-5000mV
ch = tlong / 1000; // extract volts digit
LCD_Chr(2,9,48+ch); // write ASCII digit at 2nd row, 9th column
LCD_Chr_CP('.');

ch = (tlong / 100) % 10; // extract 0.1 volts digit
LCD_Chr_CP(48+ch); // write ASCII digit at cursor point

ch = (tlong / 10) % 10; // extract 0.01 volts digit
LCD_Chr_CP(48+ch); // write ASCII digit at cursor point

ch = tlong % 10; // extract 0.001 volts digit
LCD_Chr_CP(48+ch); // write ASCII digit at cursor point
LCD_Chr_CP('V');

specifically, I can not understand the highlighted BLUE text.

Thank you all.

Regards
Sahil Khan

 

[alexxx]

I don't use PIC, but obviously it uses a 10 bit ADC (because of 1023). So you must first calculate mVolts per LSB, I suppose 5000 is the reference voltage used. So If the maximum ADC value is 1023 and the reference voltage is 5000mV, then 5000/1023 is the ADC resolution in mV. Multiplying this with the ADC result, you will get the value in mV of the ADC voltage (tlong variable in this sample program). I am not sure though, if this is the right division with 1023. Maybe 1024 is the right value, I am sure that the datasheet clarifies that in the ADC section.

 

[jayanth.devarayanadurga]

If yo use mikroC then you can use this code.

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Code C - [expand]
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unsigned char str_tlong[17];
 
//Put the below code after the line tlong = tlong / 1023; // 0..1023 -> 0-5000mV
LongToStr(tlong, str_tlong);
LCD_Out(1,1,tlong);

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The code you mentioned is extracting each digit of tlong and converting it to ascii characters and displaying it on LCD using LCD Character display function.

 

[Sahil_khan]

Thank you for your reply.

The problem is that, my reference voltage is 5V so based on that if I modify my code as follows;

tlong = (long)adc_rd*5/1023;
ch = tlong / 1; // extract volts digit

It gives me 5.005V instead of 5.000V (assuming adc_rd = 1023);

- - - Updated - - -

kindly Note the difference in the modified code i.e. 5000 is changed with 5 and 1000 is changed with 1 with reference to my initial post.

 

[jayanth.devarayanadurga]

It is better if you use float instead of long like below

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Code C - [expand]
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unsigned char str_adc_val[17];
float adc_val = 0.0, old_val = 0.0;
 
void main(){
 
 
    //TRISx setting here
    //ADCON1 setting here
 
    while(1){
 
        adc_val = ADC_Read(0);
        if(old_val != adc_val){
 
            old_val = adc_val;
            adc_val = adc_val * (5 / 1023);
            FloatToStr(adc_val, atr_adc_val);
            LCD_Out(1,1,str_adc_val);
        }
    }
}

---

 

[alexxx]

It gives me 5.005V instead of 5.000V (assuming adc_rd = 1023);

Even if there is a cast problem from the code, this doesn't seem reasonable. You get this 5005 value from the ADC read, or you see this result on the LCD? Maybe there is a problem with the LCD code, that's why I'm asking.

 

[Sahil_khan]

No actually for debugging perpose I am assigning the value instead of measuring on the pin and then debugging in Proteus.
i.e. adc_rd = 1023;

 

[jayanth.devarayanadurga]

You are getting wrong values because ADCON1, TRISx, CMCON, ANSEL, ANSELH has to be set properly. Which PIC are you using and which pin is your adc input pin?

 

[Sahil_khan]

@ Jayanth I am using PIC16F887 and I have configured all the required registers. Thank you very much.


Thank you all guys for your concern. I could not fix the problem yet but I hope it would be soon.

 

[jayanth.devarayanadurga]

Post you Circuit and Code.