This Keypad Brings T9 Predictive Text to Your PC

Some of our younger readers may not remember T9 predictive text. It was the height of mobile keyboard technology before smartphones with touchscreen keyboards came along. Even though we only had nine keys to work with, many of us were able to text much more quickly with T9 then we can with today's touchscreen keyboards. Even better, we could text by feel without having to look at the screen at all. Unfortunately, T9 has gone the way of the dodo since none of us want to sacrifice our huge touchscreens. But with a bit of work, you can build Guy Dupont's T9 keypad that works with any PC.

This keypad looks a bit like the number pad that you see on full-size computer keyboards — at least at first glance. But if you take a closer look, you will see that it actually replicates the keypad on old phones. So the "1" key is at the top instead of the bottom, each key has character labels, and the only keys aside from the numeric digits are the star and pound keys. That means that it matches the keypad that was on your old Nokia brick cellphone. But this connects to any computer via USB and appears as a standard keyboard, so you can use it to type out emails, post comments, or even to write the next great American novel.

You can build this T9 keyboard using any phone-style numeric 12-key keypad and any development board based on the Raspberry Pi Pico's RP2040 microcontroller. But Dupont's final version uses a custom PCB with Cherry MX-style mechanical key switches. A Pimoroni Tiny 2040 development board monitors the keyboard matrix and sends the characters to a PCB over USB. The only other components on the PCB are 12 diodes that prevent ghosting in the keyboard matrix. Dupont programmed the firmware in CircuitPython and it handles the complexities of deciphering the key presses. That means that as far as your computer is concerned, it is receiving characters from a normal USB keyboard.

If you're too young to have used T9, it takes some getting used to. To enter the word "dog," you would push the number 3 once, the number 6 three times, and the number 4 once. If you look at the labels below each number, you should see how those match up. The "d" is the first letter on the 3 key, the "o" is the third letter on the 6 key, and the "g" is the first letter on the 4 key. Dupont added a dictionary function, similar to the later versions of T9 with predictive features, which allows for some basic auto-correction and auto-completion. If you miss T9, this is a great way to get it back.