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PIC12F683 ADC and PWM issues

 
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Guest
PIC12F683 ADC and PWM issues
PostPosted: Sun Mar 04, 2007 5:08 am     Reply with quote
Hi, i'm having some issue in making work a really simple demo: read the voltage value from analog input and modify the PWM directly, here is the code:

Code:

void main()
{
long   value=0;

   setup_adc_ports(sAN3|VSS_VDD);
   setup_adc(ADC_CLOCK_DIV_16);
   set_adc_channel(3);    //read channel 0
   delay_us(10);
   
   setup_timer_0(RTCC_INTERNAL|RTCC_DIV_1);
   setup_timer_1(T1_DISABLED);
   setup_timer_2(T2_DIV_BY_4,24,1); //24+1*4 risoluzione pwm
   
   setup_ccp1(CCP_PWM);
   setup_comparator(NC_NC);
   setup_vref(FALSE);
   
   setup_oscillator(OSC_4MHZ);                                     

   // TODO: USER CODE!!
 
while (true)
   {
      value=(read_adc()*100)/1024; // 10 bits
      delay_ms(500);
      set_pwm1_duty(value);  //value must be long
      delay_ms(500);
   }
}


In the .h file i have:

Code:

#include <12F683.h>
#device adc=10
#use delay(clock=4000000)


The analog input is fed by a simple resistive divider (2-1Kohm around). The variable holding the read is "long", the ADC is set to 10 bit, timings and clock division should be correct... but the output isn't working as expected. From 1V to 3V the PWM works fine following the ADC value. After 3V the output fall back to 0V and starts increasing again... i've read previous post in the forum but i didn't find anything usefull. I think it's a stupid thing... but i can't find it ! :(
Ttelmah
Guest
PostPosted: Sun Mar 04, 2007 5:39 am     Reply with quote
What is the biggest value that can be held in a 'long'?. What does 100*1023 equal....

Use:

value=(read_adc()*25)/256; // 10 bits

Best Wishes
Guest
PostPosted: Sun Mar 04, 2007 4:41 pm     Reply with quote
IT works now ! you are right ! thanks !
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