The Water tolerant capacitive touch sensors

Published:2011/8/25 2:08:00 Author:Phyllis From:SeekIC

Capacitive touch sensors are commonly used in MP3 players and mobile phones. New design challenges are encountered as this technology is applied to other product categories. One of them is the operation in a wet environment such as in the dishwasher. Water tolerance is a reasonable and cost effective solution for operation in a wet environment.

Why is water tolerant, not waterproof?

Waterproof design means a product that is totally immune to water. While a water tolerant design implies that normal water levels do not interfere with sensor operation. The touch surface can tolerate the splatters and spills but not the total immersion.

In a water tolerant design, even a finger touch can produces a signal that large enough to register as a "touch". But when a boiling pot overflows and the touch surface is submerged in hot liquid, the water tolerant sensor will go wrong certainly. The submersion can be detected and the system can be alerted by properly configuring the sensor array. The safest reaction, of course, is to turn off the burner until the spill can be cleaned up.

The waterproof design, on the contrary, will continue normal working after the spill. If the user wants to turn off the burner, he needs to touch the sensor through a coating of hot liquid. The liquid may be too hot to touch, and so the burner just stays on and the pot keeps boiling, which make the situation worse.

Comparing the two approaches for reacting to a spill of hot liquid, the water tolerant design is safer and smarter.

Classification the surface wetness

The surface wetness can be divided into three types: Dry, Droplet, and Stream. Droplets forms when liquid is sprayed onto a dry surface and the liquid start to bead up. When the surface is covered with droplets, a water tolerant design is designed to operate normally. When the amount of spilled liquid is larger, the droplets merge together and form a stream.

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