External keyboard project.

[stephen_usher]

Having decided that it's going to be impossible to have the TF536 installed in a standard STFM case with the keyboard fitted etc. I've started a project to build a "two box" system based upon the original case. For this purpose I bought two of the cases @exxos had on offer.

Due to the lock-down situation it's only this week that I've really had a chance to move forward with this project. Last weekend I designed a PCB to allow the transmission of the IKBD signals over a fully populated ethernet cable. Thankfully the connections map one-to-one, with one of the eight wires not used as it's the location "pin" on the motherboard. These PCBs arrive on Monday.

The other part of the project is the keyboard itself.

On Thursday I took one of the cases into work and asked the workshop to use their band saw to remove the rear of it approximately 3mm beyond the trough separating the badge area from the rear flat part and grill. This leaves the retaining lugs for the keyboard unit in place and a thicker section of plastic onto which I can glue some 2mm thick plasticard (which also arrives on Monday). The new RJ45 pcb can be affixed to the bottom of the case with a cut-out on the plasticard back to allow access.

Overall, testing the raw keyboard in the front case without the proper wiring is still an improvement over the bare keyboard.

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I've still some work to do on the left-over lip of plastic which was the first part of the rear, flat section of the case, but a Dremel grinding wheel can be used for this.

[stephen_usher]

The IKBD-RJ45 converter boards arrived today. I'll have to make a cable between one of them and the motherboard.

I've checked with a straight through ethernet cable that each pin maps to the correct one on the other end.

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[stephen_usher]

Hmm... Doesn't work.

I see all the correct signals, power and floppy LEDs work as expected and the amplitude is fine too but there's just the continuous keyboard "click".

There must be a timing issue.

Anyone with any thoughts?

[frank.lukas]

May be a missing 10k pullup onto the TX or RX line ...

[stephen_usher]

All signals are good, crisp with sharp transitions between 0 & +5V. I can unplug the keyboard I'm using and plug it directly into the motherboard and it works fine.

The reset looks to be doing its thing too.

[stephen_usher]

OK, it was the cable between the motherboard and the interface board. The rubbish IDC connectors weren't making good contact with the wires. Pin 5 wasn't getting any connection but all the others were. I re-pressed the contact knife plate and pin 5 made contact again, but pin 2 lost contact, which is fine as that's not used.

After this it works.

I think these single row IDC connectors are designed with thicker wires in mind rather than ribbon cable.

[stephen_usher]

OK so the proof of concept works fine. I just need to make a joystick extension cable so I can put those on the back of the keyboard too so you don't have any cables underneath and also make a back plate for the keyboard case with cut-outs for the sockets.

It's so nice to be able to have the keyboard on your lap and type.

A more flexible ethernet cable would help.

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Anyway, these are the IDC connectors I was talking about:

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[stephen_usher]

P.S. if anyone wants one or two of those boards I've three PCBs and ethernet ports, so I can make up another one and a half pairs.

[stephen_usher]

Just one thing done today really, fitting one of the boards into the STFM.

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The floppy holds it firmly (but not strenuously) to the rear case so I've merely used sticky foam pads to stick it to the top of the serial DB25 socket and cut a hole in the case.

Other than that I've just put in an order for some PCBs to allow me to bring the joystick ports out to the back of the keyboard. PCBWay are advertising that their lead times have increased to ~3 days now due to a large number of orders coming in.

[Badwolf]

OK so the proof of concept works fine. I just need to make a joystick extension cable so I can put those on the back of the keyboard too so you don't have any cables underneath and also make a back plate for the keyboard case with cut-outs for the sockets.

Looks very smart from the front!

BW