Drew,

You're getting flicker at 1Mhz!?  Perhaps you've got
sections with too much happening in a single stretch
w/o changing the displayed digit?  To reduce flicker
in some of my pet feeder code (at a much lower
131.072khz) I deferred some routines to a later point
to break things up.

For example, during the ISR, after some frequency
division, I get and process the buttons, but that
could mean some calculations and some EEPROM writes.
Instead, I now grab and store the button values and
set a flag that these need to be processed.  The main
code loop checks for that flag and does the processing.
Other flags notify of data to be saved to EEPROM, or
that the 7-segment pattern for the display (stored in
registers for the mux routine to pick up and dump to
the ports) need to be regenerated, etc.

And it's set up so that if there are multiple tasks
queued up to be performed, they won't all be done in
a single stretch -- only one thing will happen during
each loop cycle.

Cheers,
-Neil.





-----Original Message-----
From: pic microcontroller discussion list
[mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Drew Vassallo
Sent: Saturday, June 15, 2002 9:51 PM
To: PICLIST@MITVMA.MIT.EDU
Subject: [PIC]: FCC exempt!


Ok, I've reduced the operating speed of my model airplane monitor down from
a 4 MHz crystal to a 1 MHz RC oscillator.  Looks like it works pretty well,
except the LED display flickers a LITTLE bit between updates because of the
overhead calculations.  No big deal, it's barely perceptible if you're not
looking for it.

So I gather that this means I'm exempt from FCC compliance, but do I still
have to perform any sort of formal testing?  Or do I just wait for the FCC
to complain and look into it on their own, only to find out that it's
exempt?

The only thing I'm at all concerned about is the fact that when I go to a
production PCB, the traces will be laid out slightly differently so the
capacitance might change the operating frequency.  I suppose I'll have to
try it and change the R value at that time.

--Andrew

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