Need help programming MCU in Winavr

I’m learning MCU programming with Atmega32 & winavr. I need to convert ADC value to something else (say voltage=5*ADCvalue/1023) which needs to deal with floating point/double. Then to display on LCD I need to convert the calculated value to string/array (eg. Sprintf(….)). Both these (floating point number & print function) consumes large memory/code area of the microcontroller (even with the small versions made for MCU).

Can any one please help me with any alternative way. I goggled a lot but failed to figure out solution specific to my case (I’m not an expert in programming/MCU).
*****
ISR(ADC_vect)
{
uint8_t thelow=ADCL;
uint16_t adc10bit=ADCH<<2 |thelow>>6;

float adcvolt=4.8*((adc10bit)/1023);
char adcvoltstr[10];
sprintf(adcvoltstr,"%.2f",adcvolt); //sprintf() may not be used
PrintValuetolcd(adcvolt,2,1); //display ADC value
PrintStringtolcd(adcvoltstr); //display volt

_delay_ms(50);
ADCSRA |=1<<ADSC; //start the next conversion
}
****

I program PIC's.. But they also have a problem with sprintf..


See if your compiler has an ftoa() function..

All else fails.... Swap to fixed point math..

ie.. 4.678 * 1000 = 4678.... then insert your own decimal point...

polashd said:

Can any one please help me with any alternative way.

Click to expand...

The alternative way is not to use floating point. Just display the raw ADC value.

Ian Rogers said:

I program PIC's.. But they also have a problem with sprintf..


See if your compiler has an ftoa() function..

All else fails.... Swap to fixed point math..

ie.. 4.678 * 1000 = 4678.... then insert your own decimal point...

Click to expand...

I tried with this solution. but its i get unexpected value . Is it because of data type.
If so, what variable type i should use?
---
uint8_t thelow=ADCL;
uint16_t adc10bit=ADCH<<2 |thelow>>6;

uint16_t adcvolt=5*((adc10bit*1000)/1023);


Printlcdval(adc10bit,1,1); //display the value
Sendastring(" "); //clear 0 of previous display
Printlcdval(adcvolt,2,1);
--
how to impliment fixed point math (sorry, I'm a newbie).

Just cast it after you have done the calculations..



Or you can miss out the floating part altogether.



Then insert your own decimal point...

polashd said:

uint8_t thelow=ADCL;
uint16_t adc10bit=ADCH<<2 |thelow>>6;

Click to expand...

Are you sure you have the ADLAR bit set? Otherwise it should be adc10bit=ADCL | (ADCH <<8);

Ian Rogers said:

ie.. 4.678 * 1000 = 4678.... then insert your own decimal point...

Click to expand...

can you please send me the code to insert decimal point (ie. within a string like 4.678)

Sure... Heres a small routine that will yield a four digit number with a decimal in position 1 with negative sign

You need to pass a string pointer with room for 7 characters...

You need to include the abs() definition ( pasted as well )