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'[PIC]: FCC exempt!'
2002\06\15@225125 by Drew Vassallo

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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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2002\06\16@023833 by Pic Dude

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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 removed}

2002\06\16@150443 by Paul Hutchinson

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There is no exemption from compliance, the exemption is from formal testing,
FCC filing and monetary penalties arising from creating the interference.

If one of your products is found to interfere with licensed equipment, the
user will be required to stop using the device. The FCC will contact you and
ask about the device. You will have to provide the FCC with enough details
about the hardware (schematics, etc.) to show that it is in an exempt class.
Your customer will not be allowed to use the device again until the
interference is reduced to a level that either satisfies the person who
filed the complaint or it meets FCC interference levels.

I've gotten the phone call from an FCC field engineer and was relieved that
the interfering product was one of our exempt devices. If it had been one of
our non-exempt products we would have been required to contact all our
customers and tell them to stop using the product until we could provide a
fix for the interference.

Paul

> {Original Message removed}

2002\06\16@204350 by Daniel Rubin

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Interesting thread...

So a PIC development board with a 20MHZ ceramic resonator may be a problem
with the FCC?   What is the solution?  Put the thing in a metal box?  Are
there tricks to keeping the radiation down such as using chokes, trace
length etc.?  Are metal can crystals less noisy than ceramic
resonators?  What type of device would a stray 20MHZ signal interfere?   Ok
enough with the 20 questions :)

Thanks
- Dan

At 03:01 PM 6/16/02 -0400, you wrote:
{Quote hidden}

> > {Original Message removed}

2002\06\17@074104 by Olin Lathrop

face picon face
> So a PIC development board with a 20MHZ ceramic resonator may be a problem
> with the FCC?   What is the solution?  Put the thing in a metal box?  Are
> there tricks to keeping the radiation down such as using chokes, trace
> length etc.?  Are metal can crystals less noisy than ceramic
> resonators?  What type of device would a stray 20MHZ signal interfere?
Ok
> enough with the 20 questions :)

EMI issues can get pretty tricky and require a lot more than 20 questions to
understand.

You have to think about everything in analog, and every wire and trace as an
antenna, including the shields of cables connected to your device.  There
are no easy answers, but a few basic strategies that should help.  A board
with a ground plane is probably the single most effective way to reduce EMI.
That way all the signal currents have an immediate low impedence return path
with a small loop cross section.  Shielding, if done right, is also very
effective although expensive.  This is usually considered the "last resort"
approach.  Note that some conducting boxes can actually cause problems by
creating slot antennas or resonant cavities.  You also have to make sure the
there is no current thru the shielding.  In other words, it is connected at
one point to the ground, preferably right where the external connections
enter the box.  Also watch external ground loops very carfully.  The list
goes on and on and on ...

If you're not comfortable with RF and the regulatory minefields, you should
consider bringing in a cosultant for those issues.


*****************************************************************
Embed Inc, embedded system specialists in Littleton Massachusetts
(978) 742-9014, http://www.embedinc.com

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2002\06\17@131304 by Dwayne Reid

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At 07:39 AM 6/17/02 -0400, Olin Lathrop wrote:
> > So a PIC development board with a 20MHZ ceramic resonator may be a problem
> > with the FCC?   What is the solution?

What about those PICs with built-in 4 MHz RC oscillators?  How does one
qualify a project built with, for example, a 12c508 and not much else.

dwayne

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2002\06\17@153451 by Drew Vassallo

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>What about those PICs with built-in 4 MHz RC oscillators?  How does one
>qualify a project built with, for example, a 12c508 and not much else.

The FCC requires that the operating frequency of the "circuit" be less than
1.7xx MHz to be exempt, I think.  Doesn't matter if it's integrated or not.
At least that's how it struck me when I read it.

Go to Harold's site and check out part 15.103  - it details everything
pretty plainly.

--Andrew

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2002\06\17@162005 by Daniel Rubin

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Are kits or boards that require some user assembly exempt... or is that
just related to UL?

- Dan

At 07:33 PM 6/17/02 +0000, you wrote:
{Quote hidden}

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2002\06\17@182112 by Harold M Hallikainen

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On Sun, 16 Jun 2002 15:01:33 -0400 Paul Hutchinson
<phutchinsonspamKILLspamIMTRA.COM> writes:
> There is no exemption from compliance, the exemption is from formal
> testing,
> FCC filing and monetary penalties arising from creating the
> interference.
>

       The low frequency battery operated exemption is an exemption from the
"technical standards and other requirements."  See
http://www.hallikainen.org/cgi-bin/section.pl?section=15.103 .

Harold

Sec. 15.103  Exempted devices.

   The following devices are subject only to the general conditions of
operation in Secs. 15.5 and 15.29 and are exempt from the specific
technical standards and other requirements contained in this part. The
operator of the exempted device shall be required to stop operating the
device upon a finding by the Commission or its representative that the
device is causing harmful interference. Operation shall not resume until
the condition causing the harmful interference has been corrected.
Although not mandatory, it is strongly recommended that the manufacturer
of an exempted device endeavor to have the device meet the specific
technical standards in this part.


Reach broadcasters, engineers, manufacturers, compliance labs, and
attorneys.
Advertise at http://www.hallikainen.com/FccRules/ .


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2002\06\18@100111 by Roman Black

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Drew Vassallo wrote:
>
> >What about those PICs with built-in 4 MHz RC oscillators?  How does one
> >qualify a project built with, for example, a 12c508 and not much else.
>
> The FCC requires that the operating frequency of the "circuit" be less than
> 1.7xx MHz to be exempt, I think.  Doesn't matter if it's integrated or not.
> At least that's how it struck me when I read it.


At first glance it might seem that a 12c508 running
at 4MHz (internal RC osc) is really running at 1MHz,
and the highest freq that can appear external to it is
1MHz. But this is not the case as the internals of
the PIC are very much driven at 4MHz, with different
processes operating on each 4MHz clock pulse. The
decoupling capacitor will be buffering current pulses
at 4MHz and the majority of the radiated energy will
be at 4MHz. :o)

Of course, for the cost of one R and one C you could
simply run the PIC at 1.5MHz with an external RC osc.
-Roman

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2002\06\18@101355 by Michael Rigby-Jones

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> -----Original Message-----
> From: Roman Black [SMTP:.....fastvidKILLspamspam.....EZY.NET.AU]
> Sent: Tuesday, June 18, 2002 2:59 PM
> To:   EraseMEPICLISTspam_OUTspamTakeThisOuTMITVMA.MIT.EDU
> Subject:      Re: [PIC]: FCC exempt!
>
> Of course, for the cost of one R and one C you could
> simply run the PIC at 1.5MHz with an external RC osc.
> -Roman
>
And the cost of using over 16% of the devices pins :o)

Mike

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2002\06\18@115157 by Harold M Hallikainen

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       In testing our products, we have generally had no problem with
radiation. The problems were with conducted EMI. So, the trick is to
filter every wire coming into the box and leaving the box. We also use
ceramic resonators with built-in capacitors and put the resonator right
next to the PIC pins it uses. Circuit boards have ground planes. All
chips have a power supply bypass capacitor at the power pin to the ground
plane. On some products, we've had to add a ferrite bead on a ribbon
cable carrying EIA422 to a rear panel connector to prevent high
frequencies from being radiated by the cable plugged in there.
       Most of our products are in metal boxes, or at least mostly metal (some
have plastic ends). One product has a PIC board inside a plastic
faceplate. There were no radiation problems until a remote control cable
was plugged in. That cable carried ground, +5V and bidirectional data on
3 wires. Bypassing ground and +5V to the chassis at the connector solved
the problem. It certainly seems the bypass capacitor to ground could have
been replaced with a short, but the test lab did not ask me before
finding the fix.
       This conducted versus radiated also seems to work as far as RF immunity.
Testing products at both AM and FM/TV transmitter sites, I've had no
problems with processor based systems operating with the cover open. Any
problems showed up when cables were plugged into the box (conducting the
RF into the box).

Harold


On Sun, 16 Jun 2002 20:36:18 -0400 Daniel Rubin <danspamspam_OUTDESIGNDEVICES.COM>
writes:
{Quote hidden}

> > > {Original Message removed}

2002\06\18@121717 by Harold M Hallikainen

picon face
       The only mention of kits I find in part 15 is
http://www.hallikainen.org/cgi-bin/section.pl?section=15.25 , which is
for "TV Interface Devices" that are kits.
       General part 15 digital device exemptions are listed at
http://www.hallikainen.org/cgi-bin/section.pl?section=15.103 .
       Home built digital devices are discussed in
http://www.hallikainen.org/cgi-bin/section.pl?section=15.23 . Note that
this does not apply to kits. In general, I believe kits must meet the
same requirements as a fully manufactured product.

Harold


On Mon, 17 Jun 2002 16:11:36 -0400 Daniel Rubin <@spam@danKILLspamspamDESIGNDEVICES.COM>
writes:
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FCC Rules Online at http://hallikainen.com/FccRules
Lighting control for theatre and television at http://www.dovesystems.com

Reach broadcasters, engineers, manufacturers, compliance labs, and
attorneys.
Advertise at http://www.hallikainen.com/FccRules/ .


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