Path: EDN Asia >> Design Centre >> Industrial/Mil/Aero >> Employ glove touch in capacitive touch UI
Industrial/Mil/Aero Share print

Employ glove touch in capacitive touch UI

01 Jul 2015  | Joshan Abraham, Vibheesh Bharathan

Share this page with your friends

Capacitive touch-sensing user interfaces are taking the place of mechanical buttons in products across consumer, medical and industrial segments. However, with the advent of touch-sensing user interfaces, end-users are demanding advanced features such as haptics support and glove touch to mimic mechanical button usage, as well as additional features such as stylus support and proximity sensing. These features improve the overall user experience of the product and offer manufacturers the opportunity to differentiate themselves. This article focuses on one of these features – glove touch, which is increasingly finding use in consumer, industrial and medical spaces. For example, the touch interface on a wearable smart band should work properly even when the user has gloves on because of cold weather conditions, or medical laboratory equipment should work properly even when touched with latex gloves.

However, implementing glove touch on capacitive touch interfaces is not easy, and most implementations tend to offer unreliable and inconsistent performance. This article focuses on the challenges in implementing glove touch on capacitive touch buttons and how these challenges can be overcome to design a robust and reliable touch-sensing interface with glove touch capability.

There are two primary challenges to implementing reliable glove touch, they are:

 • Detecting low signals produced by a gloved hand
 • Ignoring false touches from a finger hovering above the sensors

Why glove touch produces a low signal
Capacitive touch sensing works on the principle that a finger introduces a change to the capacitance of a sensor when the finger touches the overlay covering the sensor. This change in capacitance is measured and converted to the digital domain (A to D conversion) by a touch-sensing controller. When the measured value exceeds a pre-defined threshold, a touch is registered.

The change in digitized capacitance due to a finger touch is known as signal and the unintentional change in digitized capacitance without a finger touch is known as noise. A signal-to-noise ratio (SNR) of 5:1 is recommended for a reliable touch-sensing system. Figure 1 shows how capacitance is measured in a touch-sensing system.

In simple terms, capacitance introduced by a finger can be viewed as a parallel plate capacitor, where the finger and the sensor are the two conductive plates and the overlay is the dielectric medium between the plates. The finger-introduced change in capacitance is proportional to factors such as the size of the sensor and the finger (i.e. area of plates) and the dielectric constant of the overlay material; and inversely proportional to the thickness of the overlay on top of the sensor (i.e. the distance between the plates). A thicker overlay increases the distance of separation between plates, thus producing a smaller change in capacitance. This leads to a lower signal-to-noise ratio.

Figure 1: How capacitance is measured in a touch-sensing system.

Wearing a glove on a finger adds a new overlay proportional to the glove thickness on top of the existing overlay increasing the overall overlay thickness. This decreases the strength of the signal below the pre-defined threshold and a touch with a gloved hand is typically not detected. This is the reason why most users have to remove their gloves to effectively touch a button on a capacitive touch-sensing user interface.

Unwanted hover and false touches
A touch sensor can be tuned to work with thicker overlays by increasing its sensitivity. Similarly, a touch sensor can be tuned to detect a touch, even when touched by a gloved hand. Increasing the sensitivity of a sensor means that it requires a smaller change in capacitance to detect a touch.

1 • 2 • 3 • 4 Next Page Last Page

Want to more of this to be delivered to you for FREE?

Subscribe to EDN Asia alerts and receive the latest design ideas and product news in your inbox.

Got to make sure you're not a robot. Please enter the code displayed on the right.

Time to activate your subscription - it's easy!

We have sent an activate request to your registerd e-email. Simply click on the link to activate your subscription.

We're doing this to protect your privacy and ensure you successfully receive your e-mail alerts.

Add New Comment
Visitor (To avoid code verification, simply login or register with us. It is fast and free!)
*Verify code:
Tech Impact

Regional Roundup
Control this smart glass with the blink of an eye
K-Glass 2 detects users' eye movements to point the cursor to recognise computer icons or objects in the Internet, and uses winks for commands. The researchers call this interface the "i-Mouse."

GlobalFoundries extends grants to Singapore students
ARM, Tencent Games team up to improve mobile gaming

News | Products | Design Features | Regional Roundup | Tech Impact