Keypads may be really useful, but it’s just really fun to move things around on your screen with your hands. Touchscreens are popular for this very reason (not to mention that they’re really useful because whereas the “w” key on a keypad will only ever be able to type “w,” a touchscreen can change what a given area of the screen may do at any point). While smart phones and tablet PCs are nice and all, that’s not the kind of touchscreen I want. Rather, I want one that I can hook up to my computer via USB and program.
One summer I worked with a touchscreen for a testing device for the Naval Research Lab. It used a Propeller microcontroller and could take information off an SD card. The top-level language for coding it was called Spin (I still haven’t met a single person besides myself who knows Spin but they do exist according to the online forums) and there was an assembly language that I did not have the time to learn for a summer project (considering I’ve only dealt with high-level languages like Java). Even without the ability to mess with the assembly language too much I realized the great potential for this touchscreen. I was able to easily modify a demo code for a paint program to change the colors, position of the buttons, and other aspects of the user interface. After this experience, I’d like to learn the assembly language more and see what doors that opens up.
While I got to know how to work my (really the lab’s) touchscreen, I still knew very little about how touchscreens actually work. So I looked it up. There are many kinds of touchscreens that differ mainly in the way that a touch is detected. I’ll tell you about three. First, a resistive touchscreen responds to any kind of pressure (a hand or a pointer) that connects two layers and makes a noticeable change in the resistance of the circuit (1). Second, a capacitive touchscreen responds to a conductive object (a hand but not most pointers) by shedding some charge on it, which results in a detectable change in the capacitance of the circuit (1). Finally, a surface acoustic wave system uses two transducer-receiver pairs to note when a path between the transducer and receiver is broken by something touching the screen. While a resistive touchscreen is the cheapest to make, it blocks the most amount of light from passing through. On the other end of the spectra, a surface acoustic wave system is the most expensive but does not impede the light (1). (It’s easy to tell which kind of touchscreen something is between capacitive and resistive by seeing if it registers the touch from a pen).
As explaining how the place of a given touch is located is rather difficult and has just as many variations as there are kinds of touchscreens, I’ll save that for the next journal.
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