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 writes: > 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: > >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----- > > > From: pic microcontroller discussion list > > > [mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Drew Vassallo > > > Sent: Saturday, June 15, 2002 10:51 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 > > > > > > > _________________________________________________________________ > > > Send and receive Hotmail on your mobile device: > http://mobile.msn.com > > > > > > > > > >-- > >http://www.piclist.com hint: PICList Posts must start with ONE > topic: > >[PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: > ->Ads > > -- Design Devices, http://www.designdevices.com > PIC microcontroller programmers & tools, motor controllers and more! > Ebay > Deals: > http://cgi6.ebay.com/aw-cgi/eBayISAPI.dll?ViewSellersOtherItems&userid=de signdevices > > -- > http://www.piclist.com hint: PICList Posts must start with ONE > topic: > [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: > ->Ads > > 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/ . ________________________________________________________________ GET INTERNET ACCESS FROM JUNO! Juno offers FREE or PREMIUM Internet access for less! Join Juno today! For your FREE software, visit: http://dl.www.juno.com/get/web/. -- http://www.piclist.com hint: The PICList is archived three different ways. 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