On Tuesday 03 May 2005 06:44 pm, PicDude scribbled:
> 26us will give you ~38.5khz which works well with a 38khz IR receiver
> module, though I expect the range may not be as great as if you get
> 26.3khz.  I currently do this in a calculated loop (not in the ISR), bu=
t my

Oops -- meant 26.3us (not khz).


> app is a keyfob transmitter with only a few different signals.  If you =
plan
> to do much more in the PIC, you will probably need to run it at a highe=
r
> frequency.
>
> Cheers,
> -Neil.
>
> On Tuesday 03 May 2005 06:02 pm, Tom Wrighton scribbled:
> > ...  My project is to make a small IR
> > beacon as part of a robotic competition for navigation.  I would like=
 to
> > execute a small flashing LED countdown (one pulse each for 5 seconds)
> > and than modulate an IR LED for 20 seconds.  I think I have the TMR0
> > interrupt figured out and I can execute seconds timing and LED flashi=
ng.
> > My confusion comes in as follows:  I=92m trying to use the internal R=
C osc
> > (  _INTRC_OSC_NOCLKOUT  ) which I believe ends up at 1 us
> > execution cycles.  To achieve a 38KHz flash rate I need an interrupt
> > every 26.3 us.  This calculates to loading the TMR0 with something li=
ke
> > decimal 242 +/- 4 cycles for a half cycle at 38KHz.  This does not le=
ave
> > me very many cycles left for the ISR.  At this point I have tried to
> > measure the
> > frequency of the flashing LED with a Craftsman DMM that has a freq
> > measurement capability.  The best I can do so far is 32 and a fractio=
n
> > KHz. At this point I am wondering if I need to use a crystal osc. And=
 run
> > it at 10 MHz instead of the 4Mhz of the internal?  I have followed th=
e
> > PICLIST ...


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