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If a capacitive touchscreen is hit by water drops, like rain, will it report a touch?

I'm trying to evaluate what is the most appropriate touchscreen solution to use in an outdoor kiosk.

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  • \$\begingroup\$ Are you wanting to design a device or are you just wanting to buy an off the shelf device? \$\endgroup\$
    – Kellenjb
    Jul 7, 2011 at 13:29
  • \$\begingroup\$ @Kellenjb - It sounds like Pedro is trying to design a kiosk. However, all the answers are about consumer electronics. Remember, Leon, Optimal, and Mickey: This site is about electrical engineering, not about merely sharing what your phone/tablet does. \$\endgroup\$ Jul 7, 2011 at 15:26
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    \$\begingroup\$ But they presumably use similar technology to what he wants to use. What's wrong with a simple experiment to see what happens? It's a valid engineering approach. \$\endgroup\$ Jul 7, 2011 at 17:28
  • \$\begingroup\$ A capacitive touchscreen is a capacitive touchscreen, no matter what the demographic of the intended user. \$\endgroup\$ Jul 9, 2011 at 14:32
  • \$\begingroup\$ @LeonHeller, if you can explain the technology a specific variable localized to you would avoid false answers to someone designing a device. When designing a device just trusting tests of this nature itself should be cared for. \$\endgroup\$
    – Kortuk
    Jul 11, 2011 at 12:45

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My phone (SE Xperia X10) goes nuts if there's water on the screen. Even a sweaty finger can make it mis-register touches. If it's a worry I'd suggest a resistive touchscreen.

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  • \$\begingroup\$ I'm going to accept your answer because you not only did a test, but also suggested the solution of going with the resistive touchscreen. Thanks. \$\endgroup\$ Jul 11, 2011 at 13:38
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    \$\begingroup\$ Still, I bet you need to touch you phone while it's wet for it to go nuts. A water drop by itself is unlikely to do anything. \$\endgroup\$ Oct 21, 2015 at 14:29
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The short answer is if you want to use pro cap (projected capacitance) touch, you need something that has been specifically designed to not produce ghosts touches in the presence of moisture. This is considered a premium solution and they do exist but they tend to be prohibitively expensive. Search for "rugged" or "ruggedized" touch screens and you will find them.

I have worked in the touch screen industry for 4 years (N-trig) and another 4 at Synaptics doing Clickpads and touch pads. I am now at my 3rd capacitive touch company (an Austin TX based startup). Some of the stuff posted here is pseudo intellectual technobabble. Examples:

"Capacitive sensors react to the polarization of a conductor or dielectric that touches (or is close enough to) its surface...So what I'm saying is that drops of water on a touch surface won't affect it by themselves"

All of this is wrong. Capacitive digitizers react to changes in the amount of signal that is capacitively coupled from the transmit side (i.e. rows) to the receive side (i.e. columns) of the very tiny capacitor in the sensor. We call this mutual capacitance or trans capacitance (short for transmission line). This is the most common kind of capacitive sensing and it has zero to do with polarization of anything. And yes, drops of water on the sensor, if they produce signal above threshold, will cause ghost touches (which is the industry standard term for "false touches, etc.).

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Capacitive sensors react to the polarization of a conductor or dielectric that touches (or is close enough to) its surface, so the size or connection to the water should be taken into account. An isolated drop might not affect it, while a stream of water will. I have a large trackpad for my computer, and an app that visualizes its input. I put a fairly large drop onto the trackpad, and it wasn't registered. When I touched the drop, it opened a path for the electric field into my body and that activated the sensor and registered, etc.

So what I'm saying is that drops of water on a touch surface won't affect it by themselves, though your results might vary depending on the implementation. Still, water on the surface might mess things up since it could make streams, or connect with someone's finger and cause jitter. Hope that helps.

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  • \$\begingroup\$ By far the most complete answer. \$\endgroup\$
    – user36976
    Feb 10, 2014 at 16:01
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Water drop on capacitive touchscreen is usually recognized as a touch. But, there are certain ways to avoid the fault output. Try to search with "digisensor" in YouTube.

Answer is simple and clear. If we have a high resolution capacitive sensor, then we can distinguish water from human finger touch. Generalized answer to avoid water drop is not easy because it is strongly dependent upon surrounding electrical pattern. (Precisely speaking, any electric field absoption).

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I can confirm that the drool of my nine month old son also makes my Samsung Galaxy S go bananas. I seem to recall (might not be the case though) that when it has happened, the false touches seem to register further out on the display than i actually touched. Can be totally wrong there though. Also, if my memory serves me right, it never actually registered any touches when i didn't actually touched it, just that they registered wrong. Take my word with caution though. Next week when my son gets back from a trip, i can do some bug testing if you'd like ;)

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    \$\begingroup\$ This just made me laugh :D I believe I can replicate the test conditions with my five month old daughter. \$\endgroup\$ Jul 11, 2011 at 13:22
  • \$\begingroup\$ I forgot to thank you on the previous comment. Your answer was helpful, thanks. \$\endgroup\$ Jul 11, 2011 at 13:43
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Capacitive controllers can support water rejection though algorithms or sensing methodology. Generally each vendor has "secret sauce" to make it work but they expose a method to leverage that sauce. The ultimate challenge will be what volume of water do you want to allow to be present and still support touch operation. Resistive doesn't have this issue since the water does not have any interaction with their sensing method, BUT resistive has it's own challenges in the kiosk environment. Resistive is dependent on physical displacement of two layers to create a contact and therefore an electrical circuit which will wear out. Additionally depending on the type of resistive interface you may have to handle calibration and sensor drift. All solutions have their trade offs so make sure you weigh which is more important to you.

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I just tried it with my Dell Streak tablet touch-screen and it didn't do anything.

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  • \$\begingroup\$ Thanks. Your answer was very helpful to see that software might be also an important factor, not only the type of touchscreen. \$\endgroup\$ Jul 11, 2011 at 13:41

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