how to display a float value to the lcd

Simply you muliply your analog value want to see how many digits after the comma.

For example : your analog vale = 1.856

analog value *= 1000 => analog value = 1856

and after this you need to send  this value character by character in a LCD

lcd_putch(volt/1000+48); // '1'

lcd_putch('.'); // '.'

lcd_putch((volt/100)%10+48); //'8'

lcd_putch((volt/10)%10+48); //'5'

lcd_putch(volt%10+48); // '6'

thanks for your suggestion and i successfully shown the float value to my lcd now the problem is if i varied the input analog voltage  the lcd displaying value is not getting varied instantly.. its updating the varied input voltage  after switch off and on  the microcontroller.. now i need to show the lcd value instantly while i changing the input analog voltage??..

what i have to do for this????

We don't know your ADC initialization code.

• Which clock source you use for ADC10 ? (ADC10CLK/MCLK/SMCLK/ACLK)
• Did you use frequency divider ?
• Sample and Hold value (SHS_?) (4x / 16x / 64x) ?

if you answer this question. Maybe this problem will solve.

below its my source code have a look and suggest me???

void main(void)
{
   
    unsigned int res[1];
    unsigned int volt,volt1,volt2;
     unsigned int i,x=0;
    WDTCTL = WDTPW + WDTHOLD;  // Stop watchdog timer
    BCSCTL1 = CALBC1_1MHZ;    // Set range
      DCOCTL = CALDCO_1MHZ;   
       
     
    ADC10CTL1 = INCH_1 + CONSEQ_3;
    ADC10CTL0 |= ADC10SHT_2 + ADC10ON + MSC+ADC10IE;; //sample and hold time, adc on, cont. sample
    ADC10AE0 |= 0x03; // select channel A0
    ADC10DTC1 = 0x02;
   
    //ADC10CTL0 &= ~ENC;
  //  while (ADC10CTL1 & BUSY);               // Wait if ADC10 core is active
  //  ADC10SA = (int)res;
   
    //ADC10CTL0 |= ADC10SC + ENC; // start conversions
       InitializeLcm();
    ClearLcmScreen();
   
    LcmSetCursorPosition(0x00,0x00);
    PrintStr("Analog volt1:");
    LcmSetCursorPosition(0x40,0x40);
    PrintStr("Analog volt2:");
    LcmSetCursorPosition(0x54,0x54);
    PrintStr("Avg volt:");
   
   
   
 while(1)
  {
      //ClearLcmScreen();
     
    ADC10CTL0 &= ~ENC;
  while (ADC10CTL0 & BUSY);
  ADC10SA = (int)res;                            // define data buffer start
  // start ADC10 conversion
  ADC10CTL0 |= ENC + ADC10SC;
 
    for(i=0;i<2;i++)                     //code from reading from res and adding the 5 analog inputs
    {
        x=x+res[i];
    }
  
    volt1=(float)((res[0]*0.0034897) * 1000);
     __delay_cycles(200);
    volt2=(float)((res[1]*0.0034897) * 1000);
     __delay_cycles(200);
   
     x= x/2;
    volt=(float)((x*0.0034897) * 1000);
     __delay_cycles(200);
    
   
    LcmSetCursorPosition(0x0d,0x0d);
    LCD_output_result(volt1);
    __delay_cycles(200000);
   
   
    LcmSetCursorPosition(0x4d,0x4d);
    LCD_output_result(volt2);
    __delay_cycles(200000);
   
    
    LcmSetCursorPosition(0x60,0x60);
    LCD_output_result(volt);
   
    __delay_cycles(100000);
    __delay_cycles(100000);
    __delay_cycles(100000);
   x=0;
  
  }    
}

 __delay_cycles(200000);

 __delay_cycles(200000);

 __delay_cycles(100000);

 __delay_cycles(100000);

 __delay_cycles(100000);

total = 700.000 uS = 0.7 Sec + some folating point calculations = ~1second

You could try reduce delays. And check your lcd library. Maybe some long delays may include...

And try reduce sample and hold time. You use ADC10SHT_2. This means 16x ADC10CLK.

If you use ADC10SHT_0 your A/D conversion will speed up for before.

For floating point calculations this is a good way.Thanks Jens.

Jens-Michael Gross said:

Ex : ADC10MEM  = 512
volt = (float) (512*0.0034799) = 1.781733...
volt = volt * 1000 => volt = 1781

A much, much faster (yet not as accurate, at least with these values)  version is

volt = (ADC10MEM*56)>>16; 
Gives 1792 for ADC10MEM=512 and is by several magnitudes faster and does not nead any floating point operation (and not the float multiplicaiton function).
What have I done? I have multiplied the factor by 16000 and then divided the result by 16 with a shift operation (takes only 4 clock cycles).
Since 56 is a 6 bit value and ADC10MEM is 10 bit at max, the intermediate multiplication result still fits into 16 bit.

A little bit slower (as it requires 32 bit multiplication) but more accurate is the following:

volt = (ADCMEM*228058L)>>16;  // now I multiplied the factor with 65536000, the multiplication result fits into a long (28 bit size max) and the shift just takes the upper word as result.
This gives teh expected 1781. (1781.703125, to be exact, the fraction in the lower word of the multiplication result) If you want rounding, simply add 32768 before applying the shift.

[/quote]

M.Fatih INANC said:

__delay_cycles(200000);

This way, i only have to wait until this variable has increased by 1000 for a 1s delay.
And if my system clock ever changes, all I have to do is to adjust the timer interrupt, while with __delay_cycles, every single statement of this kind needs to be properly adjusted.

M.Fatih INANC said:

try reduce sample and hold time. You use ADC10SHT_2. This means 16x ADC10CLK.

The S&H time acts as a low pass filter for spikes and noice on the signal. It also relaxes the (relatively) high inrush current to the conversion buffer capacitor during sample time. If the signal source has a high impedance, it is important to give this capacitor enough time to fill (see datasheet). On ADC12, I noticed that a S&H time of 4 ADC12CLK cycles signigicantly decreases the conversion quality on higher input signal frequencies or noise levels.
Well, it depends on the situation. If there were a general solution, no engineers were needed for doing the development. (and in this case, there were no need for any SHTx choice in the ADC10 config at all)

Jens-Michael Gross said:

volt = (ADC10MEM*56)>>16

Jens-Michael Gross said:

try reduce sample and hold time. You use ADC10SHT_2. This means 16x ADC10CLK.

A reduces S&H time migh talso influence the quality of the conversion.[/quote]

 

Jens,

Which Sample and Hold value is optimized for general ADC applications ?

Due to this influence, we must always use the ADC10SHT_3 (64x ADCCLK) ?

Or this parameter may change to our application ?

 

Thanks.

Regards.

M.Fatih INANC said:

hich Sample and Hold value is optimized for general ADC applications