Reading 4 - 20 mA on LCD using PIC16F876A

be80be · Jun 15, 2011

I now remember why i quit using mikroc. The newer 8.6 pro is great but the older was like a C of it's own

aljamri · Jun 18, 2011

Hi Eric,
If you remember:

ericgibbs said:
You could remove the bottom end +1V offset in the program, give you a Span of 4V.

ericgibbs said:
I would do it in software, its cheaper and 4V is good enough.

I spare your suggestion until I got the circuit working, now I would like to know how to do it.

Thank you

aljamri · Jun 18, 2011

be80be said:

This should work for you

Code:

 char message1[] = "ADC Value= ";
 
 char *value = "0000";
 
 unsigned int ADC_Value;
 
void main() {
  ADCON0 = 0b11000000;
  ADCON1 = 0b10001111;
  TRISA  = 0xFF;              // PORTA is input
  TRISB  = 0;                 // PORTB is output
  Lcd_Init(&PORTB);                 // Initialize LCD
 
 
  do {
       adc_value = ADC_Read(0);
 
   value[0] = adc_value/1000 + 48; // Add 48 to get character value
 
   value[1] = (adc_value/100)%10 + 48;
 
   value[2] = (adc_value/10)%10 + 48;
 
   value[3] = adc_value%10 + 48;
 
   Lcd_Out(1,11,value);
 
   Delay_ms(2000);
  } while(1);
}

Hi be80be,

I let myself to play with your code as per your recommendations .

I tried to change the range 0 to 5 volts indication into 0 to 100 %, I did part of that by adding '.' and % sign but failed to change the range.

Here is Your/my code:

Code:

 char *value = "0000";
 unsigned int ADC_Value;
void main() {
  ADCON0 = 0b11000000;
  ADCON1 = 0b10001111;
  TRISA  = 0xFF;              // PORTA is input
  TRISB  = 0;                 // PORTB is output
  Lcd_Init(&PORTB);           // Initialize LCD
  do {
       adc_value = ADC_Read(0);
   value[0] = adc_value/1000 + 48; // Add 48 to get character value
   value[1] = (adc_value/100)%10 + 48;
   
   value[2] = '.';
   value[3] = (adc_value/10)%10 + 48;
   value[4] = adc_value%10 + 48;
   LCD_RETURN_HOME;
   
   Lcd_Cmd(Lcd_CLEAR);       // Clear display
   Lcd_Out_Cp(" VALVE POSITION ");
   Lcd_Out(2,5,value);
   
   Lcd_Out_Cp("%");
   
   Lcd_Cmd(Lcd_CURSOR_OFF);  // Turn cursor off
   Delay_ms(2000);
  } while(1);
}

be80be · Jun 18, 2011

The code gives a value of 0 to 1023 you have to change it to read volts

aljamri · Jun 18, 2011

Thank you be80be, I've managed to change the reading into 0-100 % range.
I'll use this as Motoroized Valve Opening Indicator. Now I'll try to raise the zero reference from 0v into 1v. Eric told me once it can be done in the software, or shall I make the hardwaew Ref- = 1v instead of 0v ? which will give me range of 1 to 5volts.

my latest resutl is attached

be80be · Jun 18, 2011

Change the part

Code:

adc_value = ADC_Read(0);

To

Code:

adc_value = ((ADC.Read(0) + 1) * 500 / 1024);

aljamri · Jun 19, 2011

It works fine using OS simulator ( see attachment in post #25 ) but in real circuit, it shows just black blocks filling the first raw of the LCD. Tried to play with the delay but not succeded. BTW, all the fuses desabled excpt for WRT which set to WRT_HALF and the oscillator set to HS.

and here is the final code:

Code:

char *value = "0000";
 unsigned int ADC_Value;
void main() {
  ADCON0 = 0b11000000;
  ADCON1 = 0b10001111;
  TRISA  = 0xFF;              // PORTA is input
  TRISB  = 0;                 // PORTB is output
  Lcd_Init(&PORTB);           // Initialize LCD
  Lcd_Cmd(Lcd_CLEAR);         // Clear display
  Lcd_Cmd(Lcd_CURSOR_OFF);    // Turn cursor off
  do {
       adc_value = ADC_Read(0);
   value[0] = adc_value/100 + 48; // Add 48 to get character value
   value[1] = (adc_value/10)%10 + 48;
   value[2] = '.';
   value[3] = (adc_value/1)%10 + 48;
   value[4] = adc_value%10 + 48;
   Lcd_Out_Cp(" VALVE POSITION ");
   Lcd_Out(2,5,value);
   Lcd_Out_Cp("%");
   Delay_ms(2000);
  } while(1);
    }

aljamri · Jun 19, 2011

The problem was a Hardware issue. The R/W has to be connected to ground, the -Vref (pin#4) has to be connected to the voltage bottom Ref ( in my case Gnd ) and +VRef ( pin# 5) has to be connected to Voltage High Ref. ( In my case 5V ), everything went fine.

I'll post some pictures as soon as I BlueTooth them from my mobile into PC.

Thank you be80be, Eric for your patient and help.

Reading 4 - 20 mA on LCD using PIC16F876A

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