We have a very paranoid customer, and have put beads on our LEDs to prevent serial data that may have coupled onto the LED signals from being modulated by the LED, and thus able to be picked up by a photo detector. Much of the paranoia was based on some studies done (for 1 example, see http://applied-math.org/optical_tempest.pdf). -John Zelno ________________________________ From: si-list-bounce@xxxxxxxxxxxxx on behalf of Don Nelson Sent: Thu 11/8/2007 6:06 AM To: zhuyongfa@xxxxxxxxxx Cc: steve weir; vijayanand@xxxxxxxxxxxxx; si-list@xxxxxxxxxxxxx; lihuafu@xxxxxxxxxx; duyumin@xxxxxxxxxx Subject: [SI-LIST] Re: LED with series bead I was once instucted to add ferrite beads to the front panel LEDs of a GigE linecard I was developing to prevent EMI (we already tested the card and passed EMI, so I was not pleased about this request). The LEDs in question were Link/Activity LEDs driven directly by the GigE PHY. When the cards came back from the factory and I began testing them, they were a complete disaster... Every once in a while, the PHY would go haywire and I'd need to reconfigure it. After a long night if pulling my hair out I realized that any time one of these LEDs switched from ON to OFF (such as pulling a fiber, causing the LINK LED to extinguish), the PHY got zapped; the ferrite caused a back-EMF into the PHY when the current tried to switch instantaneously from 15mA to 0. I replaced the ferrites with zerohms and the product worked perfectly -- and also passed EMC! -d -- Don Nelson Ericsson Warrendale, (Pittsburgh) PA, USA "There are 10 kinds of people in this world: those who can count in binary and those who can't." On Wednesday, November 07, 2007, at 11:19PM, "z46147" <zhuyongfa@xxxxxxxxxx> wrote: >Content-type: text/plain; charset=iso-8859-1 >Content-transfer-encoding: 7BIT >Steve, > >Agree with ESD susceptibility if LED applied to front panel. > >Thanks and regards. > > >Zhuyongfa >HUAWEI TECHNOLOGIES CO.,LTD. > > >Address: Huawei Industrial Base >Bantian Longgang >Shenzhen 518129, P.R.China >Tel:+86-755-89653025 >Fax: +86-755-89650731 >E-mail: zhuyongfa@xxxxxxxxxx >www.huawei.com >------------------------------------------------------------------------------------------------------------------------------------- >This e-mail and its attachments contain confidential information from HUAWEI, >which >is intended only for the person or entity whose address is listed above. Any >use of the >information contained herein in any way (including, but not limited to, total >or partial >disclosure, reproduction, or dissemination) by persons other than the intended >recipient(s) is prohibited. If you receive this e-mail in error, please notify >the sender by >phone or email immediately and delete it! > > ----- Original Message ----- > From: steve weir > To: zhuyongfa@xxxxxxxxxx > Cc: vijayanand@xxxxxxxxxxxxx ; si-list@xxxxxxxxxxxxx ; lihuafu@xxxxxxxxxx ; > duyumin@xxxxxxxxxx > Sent: Thursday, November 08, 2007 11:46 AM > Subject: Re: [SI-LIST] Re: LED with series bead > > > Beads sometimes get applied to front panel LEDs, switches and such in > the belief that this will limit EMI radiation and/or ESD > susceptibility. You can decide for yourself if you think, there is a > lot that a ferrite bead is going to do that a 100-300 Ohm current limit > resistor doesn't already do. > > Steve. > > > z46147 wrote: > > Content-type: text/plain; charset=gb2312 > > Content-transfer-encoding: 7BIT > > Hi all, > > > > I also want to know root cause of this application. > > > > Any thought on it would be appreciated. > > > > Best regards. > > > > Zhuyongfa > > HUAWEI TECHNOLOGIES CO.,LTD. > > > > > > Address: Huawei Industrial Base > > Bantian Longgang > > Shenzhen 518129, P.R.China > > Tel:+86-755-89653025 > > Fax: +86-755-89650731 > > E-mail: zhuyongfa@xxxxxxxxxx > > www.huawei.com > > > ------------------------------------------------------------------------------------------------------------------------------------- > > This e-mail and its attachments contain confidential information from > HUAWEI, which > > is intended only for the person or entity whose address is listed above. > Any use of the > > information contained herein in any way (including, but not limited to, > total or partial > > disclosure, reproduction, or dissemination) by persons other than the > intended > > recipient(s) is prohibited. If you receive this e-mail in error, please > notify the sender by > > phone or email immediately and delete it! > > > > ----- Original Message ----- > > From: Vijay Anand > > To: si-list@xxxxxxxxxxxxx > > Sent: Tuesday, November 06, 2007 6:30 PM > > Subject: [SI-LIST] LED with series bead > > > > > > Dear All, > > In our design we connect a bead in series with LED while driving from an > I/O pin. I dont know why this bead is connected ( still series resistor is > there for current limiting). Is there is any relation with EMI? Kindly do the > needful. > > With Regards, > > Vijay Anand. G > > ------------------------------------------------------------------ > > To unsubscribe from si-list: > > si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field > > > > or to administer your membership from a web page, go to: > > //www.freelists.org/webpage/si-list > > > > For help: > > si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field > > > > > > List technical documents are available at: > > http://www.si-list.net <http://www.si-list.net/> > > > > List archives are viewable at: > > //www.freelists.org/archives/si-list > > or at our remote archives: > > http://groups.yahoo.com/group/si-list/messages > > Old (prior to June 6, 2001) list archives are viewable at: > > http://www.qsl.net/wb6tpu > > > > > > > > > > -- Binary/unsupported file stripped by Ecartis -- > > -- Type: image/jpeg > > -- File: outlook_huawei_logo_en.jpg > > > > > > ------------------------------------------------------------------ > > To unsubscribe from si-list: > > si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field > > > > or to administer your membership from a web page, go to: > > //www.freelists.org/webpage/si-list > > > > For help: > > si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field > > > > > > List technical documents are available at: > > http://www.si-list.net <http://www.si-list.net/> > > > > List archives are viewable at: > > //www.freelists.org/archives/si-list > > or at our remote archives: > > http://groups.yahoo.com/group/si-list/messages > > Old (prior to June 6, 2001) list archives are viewable at: > > http://www.qsl.net/wb6tpu > > > > > > > > > > > > > -- > Steve Weir > Teraspeed Consulting Group LLC > 121 North River Drive > Narragansett, RI 02882 > > California office > (408) 884-3985 Business > (707) 780-1951 Fax > > Main office > (401) 284-1827 Business > (401) 284-1840 Fax > > Oregon office > (503) 430-1065 Business > (503) 430-1285 Fax > > http://www.teraspeed.com <http://www.teraspeed.com/> > This e-mail contains proprietary and confidential intellectual property of > Teraspeed Consulting Group LLC > > ------------------------------------------------------------------------------------------------------ > Teraspeed(R) is the registered service mark of Teraspeed Consulting Group LLC > > > >-- Binary/unsupported file stripped by Ecartis -- >-- Type: image/jpeg >-- File: outlook_huawei_logo_en.jpg > > >------------------------------------------------------------------ >To unsubscribe from si-list: >si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field > >or to administer your membership from a web page, go to: >//www.freelists.org/webpage/si-list > >For help: >si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field > > >List technical documents are available at: > http://www.si-list.net <http://www.si-list.net/> > >List archives are viewable at: > //www.freelists.org/archives/si-list >or at our remote archives: > http://groups.yahoo.com/group/si-list/messages >Old (prior to June 6, 2001) list archives are viewable at: > http://www.qsl.net/wb6tpu > > > > ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List technical documents are available at: http://www.si-list.net <http://www.si-list.net/> List archives are viewable at: //www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List technical documents are available at: http://www.si-list.net List archives are viewable at: //www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu