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newpic
Joined: 09 Aug 2005
Posts: 32
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| how to get PWM 40khz out |
 Posted: Fri Apr 29, 2011 1:34 pm |
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I use timer2, try to get 40khz out to drive an ultrasonic sensor.
Can anybody help?
| Code: | #include <16f877.h>
#fuses XT, NOWDT, NOPROTECT, NOBROWNOUT, NOPUT, NOLVP
#use delay(clock=4000000)
void main()
{
output_low(PIN_C1); // Set CCP2 output low
setup_ccp2(CCP_PWM); // Configure CCP2 as a PWM
setup_timer_2(T2_DIV_BY_16, 124, 1); // 500 Hz
set_pwm2_duty(31); // 50% duty cycle on pin C1
while(1)
{
}
} |
| Code: | | setup_timer_2(T2_DIV_BY_16, 124, 1); // 500 Hz |
what do I need to set here to get 40khz out? Explaination will helpful. |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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newpic
Joined: 09 Aug 2005
Posts: 32
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| 40khz pwm to drive ultrasonic |
| Posted: Fri Apr 29, 2011 2:15 pm |
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I got it. here is the new code
| Code: | #include <16f877.h>
#fuses XT, NOWDT, NOPROTECT, NOBROWNOUT, NOPUT, NOLVP
#use delay(clock=4000000)
void main()
{
output_low(PIN_C1); // Set CCP2 output low
setup_ccp2(CCP_PWM); // Configure CCP2 as a PWM
setup_timer_2(T2_DIV_BY_1, 24, 1); // 40kHz
/*
Crystal Frequency
PWM Freq = -----------------------------------------
(PR2 + 1) * (Timer2 Prescaler) * 4
** I need 40000 (40khz), so I need a number that 4000000 / x = 40000
so x is 100. I need to get a number (a+1)*4 = 100
a = is 24; which is (24+1)*4 = 100.
* to get duty cycle, .25 * 24 = 6,
*/
set_pwm2_duty(6); // 25% duty cycle on pin C1
while(1)
{
}
} |
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