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AT to XT Keyboard Converter

The LED was for diagnostic purposes when I was prototyping. With 6 I/O pins and 5 of them committed, you don't get many ways to signal what's going on. Once I got the thing basically working, the LED went away.

I've got a USB Chinese MIDI adapter here with not much inside but two high-brightness LEDs (red and blue) on the case (one for power, the other for signal). They do serve a purpose, but conventional LEDs (low brightness) or a single bicolor LED would have done the same thing.

If SMT components were used, this thing could be shrunk into a connector shell pretty easily.

If I were doing the PCB work for this, I'd probably modify the program to rearrange the I/O pin assignments so I could do this with a single-sided PCB. I can still do that, if it makes a difference. The only hard-and-fast pin assignments are 1,8,4 and 6.

Oh, and remember that the PIC should go into a socket--software changes, as usual, will be inevitable and the little PICs don't support ISP (too few pins).

As far as other projects go, let me give it some thought...
 
Hi Chuck, IIRC, there is hardly any difference in price between 1 and 2 sided PCB. If you'd like to do a respin though I am good for it. Putting all the traces on one side might reduce costs a bit and/or allow for a pure ground plane on the component side. I wouldn't burn any late hours on it though as it is a "nice to have".

I think the LED idea is basically OBE and gone. I could easily design the PCB for SMT but building one becomes more problematic. DIP is nice for easy construction. Wide pitch SMT is doable but still more difficult than DIP.

Yes, I agree 100% on the socket. That is essentially a given in my mind. Socket everything you can and direct solder to the PCB only the bare minimum. Soldering ICs is almost a death sentence to the part if you ever have to do an update or fix. With enough patience you can remove ICs without damaging them but I'd rather use a socket and save a lot of frustration and anxiety.

Thanks and have a nice day!

Andrew Lynch
 
Hi Andrew,

The re-assignable pins on the PIC are 2,3,6 and 7. 4 and 5 cannot be reassigned. If you wanted to make your layout easier, what pins would you change?
 
Hi Chuck! I'd leave the pins as is. I was able to route the PCB by rearranging some components and with a little arm twisting convinced it to route single sided.

Unfortunately adding the mounting holes probably chewed up all the savings from going 2 -> 1 sided PCB but it was fun anyway.

I sent the files to Hargle. They check out on the Design Rules Checker and at Design For Manufacturing. I think it is good.

Lets have everyone stomp on this design for a while and when its good I will send a final version to Hargle to go to manufacturing with.

Thanks and have a nice day!

Andrew Lynch
 
Hi! OK, no one has said anything so maybe this is totally obvious but just for full disclosure purposes... everyone realizes this design requires a "patch cable" to connect to the XT, right?

The PCB has female connectors for the AT and PS/2 keyboards so they plug straight in. However the XT side is a female connector and that will require a patch cable of some type to interface between the PCB and the XT motherboard keyboard connector.

I believe it would be a straight one to one 4 conductor cable with male DIN 5 connectors on each side. I am assuming builders would just make their own since this would be quite simple to do.

Alternatively, builders could just wire a male DIN 5 on a cable to the PCB and save two connectors. The problem with straight wiring is now the PCB is no longer detachable and has this long cable hanging off of it.

Discussion? Thoughts?

I hope this helps. Thanks and have a nice day!

Andrew Lynch
 
You can use music MIDI cables for XT class machines. they are pretty cheap to get and work just fine.
http://www.ramelectronics.net/music...midi/midi-cables/c30000-c32000-c32100-p1.html

I think the connectors on the PCB are fine. The original idea was that you could use just the flat 5 pin header that is used inside your keyboard, and mount the whole PCB inside the keyboard, but for us who want to use a KVM switch, that wouldn't do the trick, so it has to be external, with the conversion happening between the KVM and that XT itself.
 
MIDI patch cables are readily available and are 5 pin standard DIN male-to-male. I don't see this as a problem. I've got a couple in my cable hellbox that are coiled and even the right color.

There's also nothing to stop someone from taking the board, sans PC-mount connectors and pigtailing them to whatever connector (or lack of same) is desired. For example, I can see where someone might want to mount the board in a small box with bulkhead connectors or a permanently-attached cable on one end--or even mount one inside of a keyboard. My own prototype sits inside of a "Display Miser" box.
 
Hi! As long as everybody understands I am OK. Midi patch cables came to mind for me too.

However, I also have half a memory that midi cables are basically three wire serial. Would you guys please do a quick continuity check on your midi cables to see if they will work? They also need to be pin 1 to pin 1 with no cross over.

I don't have any midi cables around but I remember using them someplace before.

Thanks and have a nice day!

Andrew Lynch
 
I think a Patch cable would be fine.

Anyone that wants something different can custom build the board and add a connector something like this but smaller:

Rectangular-5-Pin-Connector.gif
 
lynchaj said:
However, I also have half a memory that midi cables are basically three wire serial. Would you guys please do a quick continuity check on your midi cables to see if they will work? They also need to be pin 1 to pin 1 with no cross over.
Click to expand...

My MIDI patch cables are old, but have all 5 wires connected. But my references show that only 4 and 5 need to be connected on MIDI cables, so you have a point.
 
likewise on my MIDI cables. easily 15+ years old, but I have actually used them that long as keyboard extension cables. All is good.
 
Hi! Are there any final comments on the AT to XT keyboard converter PCB design? If not, I'll send my final version of the gerber files to Hargle.

Please, if you have comments on the design put them in now while something can be done about them

Thanks and have a nice day!

Andrew Lynch
 
I contacted a user here who claims to be able to home-brew PCBs. I was thinking that this project might be an excellent choice for such a thign, since it's the 1st prototype. The feedback for wanting these was still under a dozen, so the $70 setup fee just to get a fab company rolling on manufacturing also makes these out of range for most pocketbooks.

So, yes, feedback we still want, but if we're able to do cheap 1-offs, then it's not the end of the world if we are making changes as we roll along...
 
Hi Hargle! You may want to consider http://www.batchpcb.com for short runs of prototype PCBs. I have not used them myself but understand from hearing others experiences they would be suited for a small run of prototypes, say 10 boards or so. Especially since they are regular shaped PCBs they would be highly efficient.

Thanks and have a nice day!

Andrew Lynch
 
I can do PCBs myself if they're traditional through-hole component density. It's pretty simple--you print the design using a laser printer on old magazine (clay coated glossy) paper, then transfer-iron the ink onto the cleaned PCB surface. Etch using a mixture of muriatic acid and hydrogen peroxide. Doesn't work too well for fine-pitch SMT, but for DIP-sized features, it's okay. Drilling the board is very tedious business, however, and the vias have to be bridged with bits of soldered-in wire--and you don't get resist or silk-screening.

I've also got photo-etch capability, but given the prices the board houses charge, it's scarcely worth the effort. Mostly, I use my PCB stock for building boxes and prototyping.
 
Hi all, I heard from this thread yesterday.
I have build various keyboard adapters in a project I have started about three years ago, www.kbdbabel.org
There is also a PS2-keyboard to PCXT protocol converter, its build with a AT89C2051.

It looks like this:
http://kbdbabel.sourceforge.net/pix/html/kbdbabel_pc_ps2_top_20061206.html
http://kbdbabel.sourceforge.net/pix/html/kbdbabel_pc_ps2_bot_20061206.html

Schematic and single side PCB layout:
http://kbdbabel.cvs.sourceforge.net...dbabel/kbdbabel-pc-ps2/89c2051-pc-ps2_sch.eps
http://kbdbabel.cvs.sourceforge.net...dbabel/kbdbabel-pc-ps2/89c2051-pc-ps2_pcb.eps

8051 source code:
http://kbdbabel.cvs.sourceforge.net...el/kbdbabel-pc-ps2/kbdbabel_ps2_pcxt_8051.asm

Cheers, Alexander
 
kbdbabel said:
Hi all, I heard from this thread yesterday.
I have build various keyboard adapters in a project I have started about three years ago, www.kbdbabel.org
There is also a PS2-keyboard to PCXT protocol converter, its build with a AT89C2051.
Click to expand...

Good work, Alexander! My goal was to use the absolute minimum of components to keep the cost as far down as possible. While the luxury of an 8051 is nice, an 8-pin PIC does very well. :)
 
Great Hierophant said:
I want to know if anyone has ever designed a converter box that will make an AT keyboard, like the most of the IBM Model Ms and other more modern 101 and 104 keyboards, work properly in a PC/XT that expect an 83-key keyboard or need a keyboard with an XT/AT switch. I have heard of boxes that will let an XT keyboard work in a modern system that expects an AT keyboard, but has the reverse been done?
Click to expand...

Good Idea but is that cost effective? I recall several of my keyboards in the past have a XT/AT switch underneath the keyboard. So I think such a task is not a big deal because it has already designed. Find the keyboard with XT/AT switch or Find out how they did it.

Dougtronics
 
Dougtronics said:
Good Idea but is that cost effective? I recall several of my keyboards in the past have a XT/AT switch underneath the keyboard. So I think such a task is not a big deal because it has already designed. Find the keyboard with XT/AT switch or Find out how they did it.
Click to expand...

Have you looked at all the postings on this topic? As we speak, the converter is going to PCB, courtesty of Hargle and Andrew Lynch.

The switchable keyboards have code to generate either in their controller firmware. On a relatively modern keyboard, it's not practical to change firmware.

However, for less than $5 in parts, you can perform the conversion. Read the rest of the thread.
 
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