Re: Keyboard Hacking - A First Part II


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Posted by Jim K on 18, 2000 at 9:48 PM:

In Reply to: Keyboard Hacking - A First Part II posted by Malberg on 18, 2000 at 1:47 PM:

: Thanks Jim K:

: Your reply was quick and helpful.

: I just want to clarify a few things, maybe I miss LED(No pun intented!! hehe) you on two of my three points, my wording was wrong!!! OOpps.

: 1)The multimeter has 2 ends one of which goes to one of the leads on the pcb board and where does the other one go? I know you mentioned the key, but where on the key? Are you talking about the mylar contact under the actual keyboard button?

yes,... where the key touches the mylar... there should be a small circle or something. The path that it takes back to the pcb is the trace. Combine the two traces and you have a keypress on the matrix.

: 2)If I start by using a wire to test 2 contacts on the pcb(1st method) or use the multimeter(2nd method) how will I know the dimension of matrix?
: For example as I mentioned to you earlier that my pcb is 20 x 8, but your saying that this may not be the case. This is the way I see it I will put one end of the wire on the first lead of 20 and the other end on the first lead of 8, and then the second lead of 8 etc etc. Isn't this going to give me a 20 x 8 matrix? Please correct me if I'm wrong.

In my experience... (now I will put a little disclaimer at the end) I just made up a box on a piece of paper. You mentioned a 20x8 layout. Therefore you probably have 28 copper connects on you pcb.. I just wrote down a 28 by 28 matrix and started testing keystrokes using keyhook (in the downloads section of this page). When I finally finshed testing every connection against its self I found that I had a lot of blank boxes on my chart but I could see a square appearing .. that will be your matrix. Matrix size really isn't that critical. The critical part is your selection of your keys. A narrow matrix just makes key selection easier. Read the faq here... there is a good writeup on ghosting. Now for the disclaimer... on my keyboard hacks I used a keyboard where the LED's were built into the pcb so I had no worries of the LED's on the mylar. If you LED's are on your mylar then one of your contacts on your pcb may be hot. Puttint a hot line onto your motherboard can be trouble. So if you use 1 wire to test with be absolutely sure where those LED's connect to the pcb.

: 3)What I meant was that because the LEDs are not on the pcb, but on the keyboard itself, is something bad going to happen when I start connecting the leads to determine my matrix? I diffently do NOT want to fool around with LEDs.

I think I answered this one above in number 2.. sorry... I have a tendancy to ramble..

: Regards -

: Malberg


Hope this is the clarification you needed. Anything more and post here and we can continue this on email... I don't think I can give you any more info without rehashing the FAQ. I'm always happy to help but we don't need to clutter the message board:)

Let me know if you need anything else.

Jim K.
Jim's Arcade Joystick



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