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ericsson_chatboard

Python utility to interface with Ericsson Chatboard CHA-10 tiny keyboard

Ever wanted to type with '90s Erricson CHA-10 rubber QWERTY keyboard? Me neither! But it costs so little that I couldn't resist.

I figured this out without an real phone, so the info might not be accurate. There are so many quirks, that I'm curious how it actually works with a real Ericsson phone.

Usage

sudo python3 chatboard.py (sudo is needed due to the module keyboard injecting keypresses for you)

Hardware

The keyboard talks serial 9600 8N1, pinout as follows: image

I've connected mine to a USB↔RS232 TTL adapter

Software

It talks AT commands, it poses as… a Mobile Equipment keyboard. It simulates keypresses on a telephone keypad. You heard me right, it "presses" numeric keys few times, to get you to the desired letter. I found a keymap of the Ericsson T18z (page 22) to be quite spot-on.

Rx

For example pressing the key 1 cycles through this sequence: ␣-?!,.:;"\'<=>()1',. Eg. pressing ? key gives you 111 on the serial. (actually: AT+CKPD="111")

Tx

In terms of communication back to the keyboard, I found that we only need to ACK anything it sends with OK

Quirks

There are many quirks:

  • on power up the keyboard is in numeric mode: it only enters digits
  • when pressing a key twice in a row, the keyboard adds 1c (or 0c) before the second sequence, to finish "entering" of the current character. 1c means space, backspace
  • pressing SMS key or eMail key causes the keyboard to enter text mode
  • there is only one case (size). shift key is used to enter special characters printer above keys. But since we have it working, we could replace those special chars with uppercase alpha letters
  • the keyboard stalls sometimes for few seconds time, queues keypresses, then releases them in a burst.
  • holding YES/NO doubles as a separate key, which is nice, but it causes the keyboard to return to numeric mode. Since I've mapped longpressing of YES to enter, you have to press SMS key (switch to alpha mode) every time you longpress YES… quirks!

I planned to use it as a quick snap on keyboard for Raspberry Pis, but it is so bad, that, I won't. I event though about writing a kernel module eventually ← Haha

Anyone knows a list of tiny keyboards? Xbox 360 had one of those attached to the gamepad,