Everybody is using smartphones and tablets these days. Whether for professional or just for personal use, since the iPhone release, back in 2007 (yes, it’s been almost ten years!), the touchscreen is an essential part of how we interact with our handheld devices.
The Apple iPhone was by far not the first device to make use of a touch-interface but it has been the product that disrupted the consumer technology landscape and user culture the most. With this article we intend to give you a basic explanation how this technology works without deep-diving into engineering lingo too much.
So, how do touchscreens work? Display technology keeps evolving around products in enterprises, in our homes and especially those for being on-the-go. How does the device know when you touched the screen, where you touched the screen, and who touched the screen?
Resistive touchscreens
In systems that are not required to support complex applications with gesture input, such as a “swipe“, manufacturers commonly deploy resistive touchscreens. They allow for users to make an input by applying pressure with their finger on a particular area on the screen.
This would commonly be the area where they programmed buttons as graphic as part of the software, running on the machine. You would often find resistive touchscreens as part of an ATM. Because this input method is prone to defects and vandalization, most commonly the user is also provided with alternative hardware buttons to enter data such as a PIN.
Resistive touchscreens require the user to press on the first layer of the display. The other side of this first layer is made of conductive material and by applying physical pressure, the spacers in between the first and second layer are pushed apart, allowing both layers to make contact at the spot, where the users pressed. This gives the machine the signal that an input has happened and where on the screen that happened.
Capacitive touchscreens
This is what you actually know from your modern smartphones, tablets and other touchscreen-enabled devices. In comparison to the resistive touchscreen, the capacitive touchscreen does not require physical pressure to be applied on the screen.
For as long your skin makes contact with the touchscreen’s surface, it won’t matter how soft or hard you press it. It will recognize the input equally. Modern capacitive touchscreens and operating systems might even be able to differentiate between a strong “tap” and a soft “tap”.
The capacitive touchscreen maintains a uniform electric field while it is active. Objects that hold an electrical charge are able to “disrupt” this field, by touching the surface, allowing for the input to happen. Even though you can’t feel your own electric charge, human skin from your finger (or any other part of your body) is also able to do that. On the other hand, you are not able to use capacitive touchscreens while wearing gloves or something else, that would cover your skin. If you want to hack your gloves, you can find plenty of tutorials and DIY explanations on the Internet.
Fingerprint processing
Sophisticated capacitive touchscreens are even able to recognize your fingerprint for a variety of uses. While this is certainly handy for quickly unlocking your phone, it could be also one of the biggest vulnerabilities. If you want to find out more on how fingerprint processing works, I recommend this deck from Vivek Hegde, based on a course by Dr. Cheng-Hsien Liu, Professor at National Tsing Hua University, Taiwan.
Photo credit: Intel Free Press / CommScope
Editorial notice: We made use of graphics from the Intel Free Press and CommScope account on Flickr for this article. We were neither sponsored by them for this article nor are we endorsing them in any way with this article.
