CCS :: View topic - Simple question on how to calculate duty for pwm to motors

FAQ

Forum Help

Official CCS Support

Profile Log in to check your private messages Log in

CCS does not monitor this forum on a regular basis.

Please do not post bug reports on this forum. Send them to CCS Technical Support

Simple question on how to calculate duty for pwm to motors

CCS Forum Index -> General CCS C Discussion

View previous topic :: View next topic

Author

Message

PCM programmer

Joined: 06 Sep 2003
Posts: 21708

Posted: Sun Jul 25, 2010 4:31 pm

Here's an example program. When I turn the trimpot from 0 to +5v,
the PWM duty cycle goes from 0 to 100%.

This line calculates the duty cycle value for the set_pwm1_duty() function:

Quote:

duty = (adc_result / 255.0) * (PR2_VALUE +1);

The expression shown in bold changes from 0 to 1.0, when I turn the
knob on the trimpot. In terms of a percentage, that's from 0 to 100%.

If you want to use a percentage number (1 to 100), you will need
to divide it by 100 (to get 0 to 1.0) so it would be the same range as
the expression shown in bold above.

Code:

#include <16F877.H>
#device adc=8
#fuses XT, NOWDT, NOPROTECT, BROWNOUT, PUT, NOLVP
#use delay(clock=4000000)
#use rs232(baud=9600, xmit=PIN_C6, rcv=PIN_C7, ERRORS)

#define PR2_VALUE 254

//==========================================
void main()
{
int8 adc_result;
int8 duty;

setup_adc_ports(AN0);
setup_adc(ADC_CLOCK_DIV_8);
set_adc_channel(0);
delay_us(20);

setup_ccp1(CCP_PWM);
setup_timer_2(T2_DIV_BY_1, PR2_VALUE, 1);
set_pwm1_duty(0);

while(1)
{
adc_result = read_adc();
duty = (adc_result / 255.0) * (PR2_VALUE +1);
set_pwm1_duty(duty);
}

}

Display posts from previous:

	CCS Forum Index -> General CCS C Discussion	All times are GMT - 6 Hours
Page 1 of 1

You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum