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ADC IN PWMMING

 
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lxc032



Joined: 12 Jul 2011
Posts: 5

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ADC IN PWMMING
PostPosted: Mon Jul 18, 2011 3:09 pm     Reply with quote
Dear All,

I'm doing a project about PWM Dimming using ADC. I'm using a variable resistor to do ADC but the dimming effect is not obvious. My code is shown as follows.

Code:


#include <16F877A.h>
#device adc=10
#use delay(clock=4000000)
#fuses XT,NOWDT,NOPROTECT,NOLVP, NOBROWNOUT,NOPUT



void main() {

int8 temp_res=0;
int8 temp_duty=0;
setup_timer_2(T2_DIV_BY_4,100,1);
set_tris_a(0xFF);*/
set_tris_c(0x00); // Set PORTC as an Output
setup_ccp1(CCP_PWM);

while(1){
set_adc_channel(0);
delay_us(20);
temp_res = read_adc(); // Get results of AD conversion
delay_us(20);                           // from channel 2 (RA2 pin)

temp_duty = (temp_res); // Convert the 10 bit value
set_pwm1_duty(50);
delay_us(10);
}
}





Should I change the mutiple of (temp_res) to make the effect more obvious?
PCM programmer



Joined: 06 Sep 2003
Posts: 21708

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PostPosted: Mon Jul 18, 2011 3:26 pm     Reply with quote
Here is a working program which reads the ADC and sets the PWM
duty cycle to dim an LED:
http://www.ccsinfo.com/forum/viewtopic.php?t=40007&start=1
lxc032



Joined: 12 Jul 2011
Posts: 5

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PostPosted: Mon Jul 18, 2011 3:46 pm     Reply with quote
Thanks for your program.

I'm trying to use a variable resistor to change the duty cycle of the PWM signals. Should I need to change the multiple of the "temp_res" ?
PCM programmer



Joined: 06 Sep 2003
Posts: 21708

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PostPosted: Mon Jul 18, 2011 3:51 pm     Reply with quote
You are not using the adc value to set the PWM duty. You are doing
nothing with it. Your PWM duty is set to a constant value of 50.

The program that I gave you in the link does use the ADC value
to set the duty. I suggest that you study it.
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