With each tap, a small electrical current passes from the screen to her hand. Because electricity flows easily through human bodies, sensors on the phone register a change in voltage wherever her thumb presses against the screen. But the world is messy, and the phone senses random fluctuations in voltage across the rest of the screen, too, so an algorithm determines the biggest, thumbiest-looking voltage fluctuations and assumes that’s where she intended to press.
So she starts tap-tap-tapping on the keyboard, one letter at a time.
I’ve long been a fan of “full story” examinations of how technology works. This one looks and the sending and receipt of an SMS text message from concept through touchscreen, encoding and transmission, decoding and display. It’s good to be reminded that whatever technology you build, even a “basic” Arduino project, a “simple” website or a “throwaway” mobile app, you’re standing on the shoulders of giants. Your work sits atop decades or more of infrastructure, standards, electronics and research.
Sometimes it feels pretty fragile. But mostly it feels like magic.