Pico based serial/USB keyboard membrane emulator.

[stephen_usher]

Over the last week I've been working upon a way of talking to a bare BBQL motherboard from another system.

Well, as of today I can do so with a prototype system...

Currently I can plug the Pi400 into the PIco's USB port and use minicom so that I can type on the machine as if I'm using the keyboard, well, other than no ALT key as there's no way that ASCII can translate to that really.

The QL's matrix is effectively just 8 scan lines and 8 sense lines. The Shift, Ctrl and Alt keys map into sense line 7.

One problem I had was that the matrix diagram I had to map the matrix to keys was wrong. It had 1 and 3 transposed, similarly 9 and o.

The other thing to note is that to enable one of the modifier keys you first have to enable them on their own before ORing them with the key code data.

Anyway, I've designed a more generalised PCB (which can handle up to 12 sense lines) which also adds an RS232 port. Once I can move stdio over RS232 then I can develop the USB HID code to allow the use of USB keyboards and do away with an extra machine.

Hopefully the PCBs will arrive around the end of the week and I can move away from the RatsNest(tm).

[stephen_usher]

The boards arrived just after lunch, so I quickly built one up. Just a minor issue with the DB9 sockets I bought overlapping one of the header positions, but nothing a pair of wire cutters couldn't fix.

The good news is that it works at least as well as the breadboard version so far. I've not tested the RS232.

[stephen_usher]

And the RS232 works... though when the board is powered by the PicoATX power supply the 74LS244 didn't get power as it seems that the Pico doesn't power the VBUS line if powered by VSYS, so a bodge wire was necessary.

[Popopo]

I like it. Congrats for successful development

For what the serial port?
Would not save resources (in this case) to use the Arduino Nano? for power and signal level compatibility.