Hello All,

=20

I=92m a newbie, hobbyist, nonprofessional and retired.  I make these

declarations up front so you might take my query with a grain of salt.

I=92m still working on my 1st PIC project, though at this point I feel I =
have

learned a lot (for me anyway). I bought a PICkit-1 after seeing it at one=
 of

our robot club meetings.  As many of you know it comes equipped with a

12F675.  I have become obsessed with using it for my project idea, and al=
so

to program it with assembly language.  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 flashing.

My confusion comes in as follows:  I=92m trying to use the internal RC os=
c

(  _INTRC_OSC_NOCLKOUT  ) which I believe ends up at 1 us

execution cycles.  To achieve a 38KHz flash rate I need an interrupt ever=
y

26.3 us.  This calculates to loading the TMR0 with something like

decimal 242 +/- 4 cycles for a half cycle at 38KHz.  This does not leave =
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 fraction KH=
z.

At this point I am wondering if I need to use a crystal osc. And run it a=
t

10 MHz instead of the 4Mhz of the internal?  I have followed the PICLIST

for several months and am very impressed with the expertise and graciousn=
ess

of the membership.  Up front: any and all comments and guidance you might

offer will be greatly appreciated.

=20

Best Regards and Thank You,

=20

Tom Wrighton

Crystal Lake, IL, USA



__________________________________________________
Do You Yahoo!?
Tired of spam?  Yahoo! Mail has the best spam protection around=20
http://mail.yahoo.com=20
--=20
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist