imaclmaca / sharpfw-620-kbd

A Pico 2040 tool to decode the keyboard matrix of an old Sharp FontWriter to USB

Sharp FontWriter-620

Use a Raspberry Pico to decode the keyboard matrix of an old Sharp Fontwriter

I have an old Sharp Fontwriter-620 I picked up on eBay for £15 (which mostly still works, even the 3.5" floppy disk, but it is virtually impossible to get printer ribbons for them any more.)

So I'm "refurbishing" it with a Raspberry-Pi internally, and losing the old printer mechanism and the FDD.

It has quite a nice keyboard (albeit early 90's rubber dome, not actual switches) so I created this basic Pico tool to decode the matrix and allow me to use it as a basic USB keyboard. The 90's Sharp keyboard layout is somewhat "idiosyncratic", so I have made some accommodations to allow for that here.

The code here attempts to "interpret" the more unusual of the FontWriter keys and then emit (to the USB HID interface) various key combinations that (at least for a Debian-based Linux with a UK key map loaded) produces the "expected" symbol on the screen.

FWIW, I doubt this will work quite right with anything other than a UK-key map under Linux, though the basic key mapping (i.e. for the non-weird keys) is likely to be just fine. In particular, I doubt this will would produce the expected combined keys under Windows, which tends to use different mappings (though again the "basic" keys should all be fine.)

Note, also, that the matrix has no diodes between the lines, so if you press too many keys you can get weird shadow key effects. I've tried to trap for that, but offer no guarantees.

Just, do not use this as a gaming keyboard, basically. It's fine for actual typing!

Notes on Function Keys and Modifiers

The FontWriter keyboard has no function key row, so to accommodate that I have repurposed the "HELP" key for this purpose, as a modifier; basically, hold down the HELP key then press any of 1 - 0 to get FN1 to FN10. I haven't provided a hook for F11 or F12 though...

With the FontWriter, to access the code-II keys, you had to press and release the II key, then press the modified key. Instead I have implemented it as a regular modifier key here, that is you need to press and hold the II key whilst pressing the key you want.

There is no ESC key on the FontWriter keyboard, so the "Cancel" key is mapped to that instead.

The "Edit/Del" key is mapped to DEL.

The "Block" key is not used at present - the block selection function of the FontWriter is interesting, but supported in other ways these days!

The LEFT "Menu" key is mapped to ALT. The RIGHT "Menu" key is mapped to WIN / SYS.

The CTRL keys are mapped "normally".

There is no Right-ALT (AltGr) or Menu key option.

There is no Print Screen, Scroll Lock or Pause key option (but who uses them anyway?)

Hardware configuration

The Sharp FontWriter keyboard matrix is basically an 8 x 10 mapping, though not all 80 possible key positions are used.

I initially planned to use the Pico PIO to scan the matrix, but given that an 8 x 10 matrix only needs 18 GPIO lines, and the Pico has plenty more GPIO than that, I just scanned in software as an initial test - which worked well enough, so the PIO version never happened.

The Pico drives each of the 10 columns in turn, then checks the 8 rows for the pressed keys. It then determines the key(s) that are required and sends them to the USB as a pretty basic HID keyboard device.

(This only does the HID version of the bInterfaceSubClass, it does not do the "Boot Interface Subclass" version, so it is probably not a good idea to use this to access the BIOS of your old PC...)

It is fine for my needs!