An effective method of bypassing the problem which we have implemented at
times is to issue a reset periodically (milliseconds) to reset the USB
line. This adds a bit of software overhead and sometimes the driver is not
yours to change but it works well.
Bob Heller
3M EMC Laboratory, 76-1-01
St. Paul, MN 55107-1208
Tel: 651- 778-6336
Fax: 651-778-6252
=======================================================================
----- Forwarded by Robert E. Heller/US-Corporate/3M/US on 01/06/2010 04:59
AM -----
From: Curt McNamara <[email protected]>
To: John Cochran <[email protected]>
Cc: "[email protected]" <[email protected]>
Date: 01/05/2010 10:32 PM
Subject: Re: ESD Test Failure of Stainless USB Mouse
Sent by: <[email protected]>
Look at the grounding of the USB connector on the computer. If someone has
tried to be clever :-) and tied this to something other than the common /
digital ground then you often see these problems.
Curt
On Jan 5, 2010, at 12:13 PM, John Cochran wrote:
During testing of an industrial control system, with a custom
stainless steel USB mouse, ESD testing failed. The standard used was
IEC 61000-4-2, Electrostatic Discharge. When a -4KV discharge was
applied to the metal housing of the mouse, the mouse and/or USB
keyboard would stop functioning. The function returned after
testing, only if the USB connection to the computer was broken and
connected again. Suspected the ESD charge was disrupting the USB
communication in the computer, since the cable shield is the only
path to earth ground. Tried to break the cable shield and connect
the mouse end to the enclosure (earth ground), with no improvement.
Looped the cable through an Intermark RFC-20 ferrite which helped to
pass testing, marginally. Does anyone have any good suggestions for
eliminating the interruptions causes by a contact ESD discharge on a
metal shelled USB mouse?
John Cochran
215-443-3400 x193
-
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