PWM Question

[Andrew Welch]

I want to use CCP1 in PWM mode to generate a 38khz pulse on an IR emitter. I'm using a 20mhz 16F877.

Is this possible? If so, what is the set up code? I'm having a hard time figuring that out.

Thanks...
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This message was ported from CCS's old forum
Original Post ID: 11465

[PCM programmer]

:=I want to use CCP1 in PWM mode to generate a 38khz pulse on an IR emitter. I'm using a 20mhz 16F877.
:=
:=Is this possible? If so, what is the set up code? I'm having a hard time figuring that out.
----------------------------------------------------

Try this:

#include "c:\program files\picc\devices\16F877.h"
#fuses HS,NOWDT,NOPROTECT,PUT,BROWNOUT, NOLVP
#use Delay(clock=20000000)
// #use rs232(baud=9600, xmit=PIN_C6, rcv=PIN_C7, ERRORS)

//===============================================
main()
{

output_low(PIN_C1);

setup_ccp1(CCP_PWM); // Configure CCP1 as a PWM

while(1)
{
setup_timer_2(T2_DIV_BY_1, 130, 1); // 38 KHz
set_pwm1_duty(65); // 50\% duty cycle

while(1);
}
___________________________
This message was ported from CCS's old forum
Original Post ID: 11482

[Neutone]

:=:=I want to use CCP1 in PWM mode to generate a 38khz pulse on an IR emitter. I'm using a 20mhz 16F877.
:=:=
:=:=Is this possible? If so, what is the set up code? I'm having a hard time figuring that out.
:=----------------------------------------------------
:=
:=Try this:
:=
:=#include "c:\program files\picc\devices\16F877.h"
:=#fuses HS,NOWDT,NOPROTECT,PUT,BROWNOUT, NOLVP
:=#use Delay(clock=20000000)
:=// #use rs232(baud=9600, xmit=PIN_C6, rcv=PIN_C7, ERRORS)
:=
:=//===============================================
:=main()
:={
:=
:=output_low(PIN_C1);
:=
:=setup_ccp1(CCP_PWM); // Configure CCP1 as a PWM
:=
:=while(1)
:={
:=setup_timer_2(T2_DIV_BY_1, 130, 1); // 38 KHz
:=set_pwm1_duty(65); // 50\% duty cycle
:=
:=while(1);
:=}

Do you want to use a PWM frequency that is 16 times the bit time? The part I use does.

<a href="http://www-s.ti.com/sc/ds/tir1000.pdf" TARGET="_blank">http://www-s.ti.com/sc/ds/tir1000.pdf</a>

bit time 1/(9600)
PWM would be 1/(9600*16)
or 153.6 KHz

bit time 1/(2400)
PWM would be 1/(2400*16)
or 38.4 KHz

It would also help to use a crystal that makes your baud rate and iRDA clocl without errors.

#define XTAL_FREQUENCY 19660800
#use delay(clock=XTAL_FREQUENCY)
___________________________
This message was ported from CCS's old forum
Original Post ID: 11485

[Andrew Welch]

:=:=I want to use CCP1 in PWM mode to generate a 38khz pulse on an IR emitter. I'm using a 20mhz 16F877.
:=:=
:=:=Is this possible? If so, what is the set up code? I'm having a hard time figuring that out.
:=----------------------------------------------------
:=
:=Try this:
:=
:=#include "c:\program files\picc\devices\16F877.h"
:=#fuses HS,NOWDT,NOPROTECT,PUT,BROWNOUT, NOLVP
:=#use Delay(clock=20000000)
:=// #use rs232(baud=9600, xmit=PIN_C6, rcv=PIN_C7, ERRORS)
:=
:=//===============================================
:=main()
:={
:=
:=output_low(PIN_C1);
:=
:=setup_ccp1(CCP_PWM); // Configure CCP1 as a PWM
:=
:=while(1)
:={
:=setup_timer_2(T2_DIV_BY_1, 130, 1); // 38 KHz
:=set_pwm1_duty(65); // 50\% duty cycle
:=
:=while(1);
:=}

Thanks very much! I'll give it a try. I wasn't sure of the right parameters for setup_timer.
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This message was ported from CCS's old forum
Original Post ID: 11504