38Khz IR carrier - best way to turn it on and off

[ardhuru]

Hi,

Here's what had worked for me. Richard is right, you cant use HPWM for frequencies above 32.768khz.

Set the registers as follows.

TRISC.2 = 0 ' CCP1 (PortC.2 = Output)
PR2 = 25 ' Set PWM Period for approximately 38KHz
CCPR1L = 13 ' Set PWM Duty-Cycle to 50%
CCP1CON = %00001100 ' Mode select = PWM
T2CON = %00000100 ' Timer2 ON + 1:1 prescale

This would give you a continuous 38khz on the pwm pin, at 50% duty cycle.

Now, toggle TRISC.2 between an input and an output at 1ms.

Hope it works! If it does, thanks go to Bruce Reynolds. If doesnt, brickbats to me!

Regards.

[richard]

that would be for fosc=4
for my money I'd say :
CCPR1L = 52 ' Set PWM Duty-Cycle to 50%
{mister_e pic multi-calc}

[mark_s]

As Ardhuru said, credit to Bruce Reynolds for publishing some great projects.

Maybe you can gets some ideas here.
http://wayback.archive.org/web/20120...com/remote.htm

[andywpg]

Hi,

Here's what had worked for me. Richard is right, you cant use HPWM for frequencies above 32.768khz.

From what I understand of what was quoted, 32768Hz was maximum WITHOUT using longs. I'm using an 18F2550, and when I compile, I get the following message:

'[MESSAGE]pic18f2550.pbpinc(285): LONG Variables enabled (PBPL used)'

It seems like it used longs because of the frequency I specified, and it seemed happy. Anyway, the problem is solved, see my last post.

Thanks for the help!

[andywpg]

Thanks Everyone!

It worked!

The answer was a pull down resistor. It got rid of that slope. I tried a few, and worked out that 4.7K was the highest value I could use. That gave me a final voltage about 4.2V which should be fine.

Then I had to play with the frequency I specified to get exactly 38 pulses in 1mS. Even though the scope's measurement function still reports it as 38.46KHz - I told you it was a cheap scope!

Here are two images of what I have now.

Thanks again!

Andy

Attachment 8114

[richard]

- I told you it was a cheap scope!

the scope is actually correct.

38.462KHz is as close as you can get to 38KHz hpwm with a 4MHz osc

[andywpg]

the scope is actually correct.

38.462KHz is as close as you can get to 38KHz hpwm with a 4MHz osc

I'm using the 8Mhz internal oscillator. I'm curious how you figured that out though, could you educate me?

What if I used a 10 or 16Mhz crystal? I have both on hand.

[richard]

search the forum for PicMultiCalc by mistere

@8m you can get 37.736 KHz , 38.462 KHz
@16m 38.095 KHz , 38.462 KHz
@10 37.879 KHz , 39.063 KHz