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zonemikel
Joined: 13 Oct 2007
Posts: 53
Location: Texas
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| Cant cast or print float in printf |
 Posted: Thu Jul 29, 2010 2:14 pm |
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I'm trying to take the adc value and make it a float but every time i try and cast it It wont print. I've tried it several different ways but this is one, any idea why ?
| Code: | // global variables for this .h
int8 battVolts = 0;
int8 chgVolts = 0;
unsigned ChgSec = 0;
void chargeBattery(){
set_adc_channel(13); // vdivider hooked to battery (39/(47+39))*vin
// reset vars, if not it will hold the last value
battVolts = 0;
chgVolts = 0;
// turn off charge input and read battery
output_high(CHGPIN);
delay_ms( 900 );
// if negative delta v or one hour stop charging and go to idle state
if(battVolts < read_adc() || ChgSec > 3600){
printf("Battery Charged!, NDV detected in %u Seconds", ChgSec);
state = '0'; // return to idle state
}else{ // continue charging
battVolts = read_adc(); // latest battery voltage
// turn on charge input and read charge voltage
output_low(CHGPIN);
delay_ms(50);
chgVolts = read_adc();
printf("\f Chg: %u Batt: %u %f ",chgVolts,battVolts,(float)battVolts/255*5); // <<<-- this line !!!!
}
} |
I'm on a '887 and using #adc=8
Thanks for your time
_________________
Smart people know how stupid they are. |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Thu Jul 29, 2010 2:25 pm |
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Some versions of the compiler require that you put in a width and a
precision field for "%f". Also, the width field must be at least one
greater than the precision field. Try this:
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zonemikel
Joined: 13 Oct 2007
Posts: 53
Location: Texas
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| Posted: Thu Jul 29, 2010 2:36 pm |
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Nope that didnt work ... it just prints nothing where it should print the float
Chg: 183 Batt: 0 time:69
Chg: 183 Batt: 0 time:70
Chg: 183 Batt: 0 time:71
Chg: 183 Batt: 0 time:72
Chg: 183 Batt: 0 time:73
with
| Code: | | printf("\f Chg: %u Batt: %7.3u time:%Lu ",chgVolts,(float)(battVolts/255)*5/.453,ChgSec); |
never mind just saw the 'u' ...
ok now it just prints like it did before cutting off everything after the float
Chg: 182 Batt:
Chg: 182 Batt:
Chg: 182 Batt:
| Code: |
printf("\f Chg: %u Batt: %7.3f time:%Lu ",chgVolts,(float)(battVolts/255)*5/.453,ChgSec); |
_________________
Smart people know how stupid they are. |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Thu Jul 29, 2010 2:55 pm |
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| Code: | | (float)(battVolts/255)*5/.453 |
This is going to give you 0, most of the time. battVolts is an 'int8'.
So, say it's 100. Then 100/255 in integer math is 0. Then you
cast it to a float. But you're just casting a 0 to 0.0, and then multiplying
0.0 * 5 and doing the division still gives 0.
My advice is to make a little test program that only does the math and
displays it. Play around with it. Get it right, and then integrate it into
the rest of your program. Example:
| Code: |
#include <16F887.H>
#fuses XT, NOWDT, NOPROTECT, BROWNOUT, PUT
#use delay(clock=4000000)
#use rs232(baud=9600, xmit=PIN_C6, rcv=PIN_C7, ERRORS)
//===========================
void main()
{
int8 battVolts;
float result;
battVolts = 100;
result = (float)battVolts/255*5;
printf("result = %7.3f \r", result);
while(1);
}
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If this doesn't help, then post your compiler version. |
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