2 AA batteries are not going to cause magnetic coupling at 50 Hz. Faraday says it ain't so.
> From: [email protected] > Reply-To: [email protected] > Date: Tue, 29 Jul 2003 09:34:29 -0600 > To: <[email protected]>, <[email protected]> > Subject: RE: self blinking LEDs as EMI sources WAS: LED lamps > > > I wonder if the self blinking LEDs might have an oscillator running at roughly > 50 Hz. And, the signal pick up could be magnetic field coupling to the > telephone. > > Dave Cuthbert > Micron Technology > > -----Original Message----- > From: Wan Juang Foo [mailto:[email protected]] > Sent: Friday, July 25, 2003 9:37 PM > To: [email protected] > Subject: self blinking LEDs as EMI sources WAS: LED lamps > > > > Dear All, > I observe recently that some self blinking (and color changing) LEDs 'are' > what seem to be a substantial emitters of radiated emission/interference. > These LEDs are rigged up by hobbyists as decorative illuminators and acts > more or less like the blinking lights for Christmas trees. I observe that > each of theses circuits can be made to hung like Christmas tree ornaments. > > I came across a situation where the telephone lines were 'substantially > noisier' :-) when several sets of battery operated circuits was about 3 m > away from the telephone. It is not a very scientific method but I did a > quick check and found by the method of elimination ;-) or what some would > call systematic trials to find the source of the problem. It took me by > surprise that the LEDs had a substantial role to play in the interference. > LED circuits gets connected (on), hum gets louder. LEDs circuits gets > disconnected, hums gets quieter and so on and so forth... > > These are very simple circuits with a single resistor and the LED in > series. The 2 AA sized NiCad battery with holder, single resistor and LED > including wire, total length about 5", tip to tip. These circuits were > found to (well at any rate, seems to) emit interference that cause a > telephone to pick up (50Hz) hum! It looks like the mains hum was pick up > and modulated by the 'device' and reradiated or broadcasted... > > I can see that the blinking action at about 1 Hz have a duty cycle and that > may generate a lot of ringing but what is surprising is the interference > finding its way into the a telephone handset! I find it hard to believe > that how the 'carrier' of the mains hum can eventually gets demodulated a > puzzle. > > One wonders what can be observed if I get the circuits to a OATS? There > again, how do I recreate the 50 Hz environment to couple the mains into > these LED circuit? I had the Helmholtz coil in mind but can that be > 'treated' as part of a test setup? > > Did anyone here have similar observation? One wonders if there any 'product > specific standards' for such battery operated device that uses LEDs as > decorative illuminators. > > :-) > > One wonders what will happen if there are such gadgets line up to 'hit' the > market this Christmas... > > Looks like there will be a lot of testing work coming for EMC engineers! > > Tim Foo > > > > > > > ------------------------------------------- > This message is from the IEEE EMC Society Product Safety > Technical Committee emc-pstc discussion list. > > Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ > > To cancel your subscription, send mail to: > [email protected] > with the single line: > unsubscribe emc-pstc > > For help, send mail to the list administrators: > Ron Pickard: [email protected] > Dave Heald: [email protected] > > For policy questions, send mail to: > Richard Nute: [email protected] > Jim Bacher: [email protected] > > Archive is being moved, we will announce when it is back on-line. > All emc-pstc postings are archived and searchable on the web at: > http://www.ieeecommunities.org/emc-pstc > > > ------------------------------------------- > This message is from the IEEE EMC Society Product Safety > Technical Committee emc-pstc discussion list. > > Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ > > To cancel your subscription, send mail to: > [email protected] > with the single line: > unsubscribe emc-pstc > > For help, send mail to the list administrators: > Ron Pickard: [email protected] > Dave Heald: [email protected] > > For policy questions, send mail to: > Richard Nute: [email protected] > Jim Bacher: [email protected] > > Archive is being moved, we will announce when it is back on-line. > All emc-pstc postings are archived and searchable on the web at: > http://www.ieeecommunities.org/emc-pstc > This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: [email protected] Dave Heald: [email protected] For policy questions, send mail to: Richard Nute: [email protected] Jim Bacher: [email protected] Archive is being moved, we will announce when it is back on-line. All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
