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[RFI] Touch control laundry machines

To: rfi@contesting.com
Subject: [RFI] Touch control laundry machines
From: dgsvetan@rockwellcollins.com
Date: Tue, 6 Nov 2007 17:05:23 -0600
List-post: <mailto:rfi@contesting.com>
Those of us who are regular readers of this reflector know that there have 
been a number of hot topics over the past few years, among them RFI from 
laundry equipment (especially the newer multi-speed electronically 
controlled washers and dryers) and the long-infamous touch lamps.  For 
those new to the group, touch lamps operate by the changes produced on a 
circuit when a person touches a metallic part of the lamp, causing the 
lamp to turn on or off, or to change brightness.  The coupling mechanism 
for the touch control is capacitance, and the infamy comes from the fact 
that in all too many instances, the metal lamp part to be touched and its 
associated wiring are very nice antennas that can result in bizarre and 
unexpected bahavior of the lamp when RF is created by nearby RF 
transmitters.  In some cases, the lamps have become sources of RFI that 
cause problems to HF reception.

It now appears that these two marvels of modern technology are getting 
married by Haier into laundry machines that feature touch control. Today's 
"Designfax Line" newsletter contained an article about this development. 
Two brief excerpts:

âCypressâs CapSense is used in our washing machinesâ touch-sensing 
buttons,â says Xu Sheng, director of technology development department, 
Haier Washing Machine Business Unit. âAmong all white goods, washing 
machines face the most severe operating environment. Haier has very strict 
reliability requirements for touch sensing input solutions, and CapSense 
was selected over other solutions because of its flexibility, reliability, 
and performance in the presence of humidity, vibration, high temperature, 
and interference.â

Capacitive sensing is fast becoming the solution of choice for front-panel 
display and media control applications. Increased durability, decreased 
bill of materials (BOM), and a clean, minimalist appearance make this 
elegant interface attractive to a wide range of designs. With Cypressâs 
CapSense interface, a finger on the interface forms an electrical 
connection with embedded sensors, which work with the PSoC device to 
translate data about the fingerâs presence into various system control 
functions. The sensor itself is a copper pad on the PCB, not an actual 
component. All of the circuitry for controlling the sensor is inside the 
PSoC device."

There are two good tidbits of news here:  1) Note the mention of the word 
"interference" at the end of the first excerpt.  True, we don't know if 
that includes both interference to and from the device, but at least they 
know enough to say the word.  2) Cypress Semiconductor, the maker of the 
CapSense system being discussed, is a US-based company.  Yep, US selling 
to China (although it would not surprise me to learn that the chips 
themselves may very likely be made either in China or one of the nearby SE 
Asian countries).

There are some rudimentary drawings included with the article.  The 
implication is that human contact is to a pc board conductor (with an 
intermediate insulating layer for safety).  The "brains" of the touch 
decoding (which sensor pad commands which functions) are in the Cypress 
device.  No mention is made of what technology the CapSense device uses or 
how it reduces interference potential. 

Hopefully, some list members will archive this info for later reference. 
It would be very interesting to know if anyone ends up with one of these 
machines and just how well it works with respect to laundry time and 
operating time.

73, Dale

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