This guide will show you the how to make a cheap, ugly input device for your computer. In this I am using a monome 40h logic board to send the signals to the computer from an eight by eight grid of buttons, but these plans could easily be modified to make a keyboard-format grid using a donor chip from an old keyboard.
I hadn't ordered any parts to make my custom monome 40h but did have the chip, so impatience was the mother of invention.
If you've ever looked inside of a computer keyboard before (if you haven't, you should- it's very fun) somewhat know the mechanics behind it. The type of keyboard this instructable is based around is the membrane keyboard. Check out the wikipedia article on membrane keyboards for more information on this.
How long: one or two hours most likely, maybe more if you don't want it as ugly as mine
---1 encoder board- i used the monome 40h logic board (has led feedback for each key) but any old chip from an old keyboard would work
---wire- you will notice that in the pictures i used bare wire. this is NOT smart as it makes it very difficult to do anything without the signals getting crossed, but that is all i had.
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Step 1: Template and Holes Layer
While not absolutely necessary, a template is great help, especially if you're doing something more complicated than an 8 by 8 grid (like a keyboard). I used a total of three templates but only one is needed for this step. If you need an idea for a template, check the membrane layout inside a keyboard or the simple temple I provided.
Slide the holes template into a page protector and use a hole punch to make an opening at each junction. Most hole punches won't make it past the first row so use a paper cutter to make a line between each row. As long as you don't cut the edges the page protector should stay managable. After you finish all holes you can remove the template (or leave it if you think it could use the thickness).
The point of this layer in a membrane keyboard is to seperate two layers of contacts. When a force pushes down one layer into the hole, a circuit is completed and the chip recognizes the key press.
Step 2: Conductive Layers
While actual membrane keyboards use some sort of conductive traces, this will use tin foil because everybody has it and nobody has conductive paste or whatever that stuff is (although the design could be greatly improved if one actually did have that stuff).
For my design, the paths for each layer were quite simple. If you are attempting to make a keyboard, I wish the best of luck to you if you try to do that with tin foil (just look at the traces in a real keyboard... complex). Anyways, for this layout you need one vertical layer and one horizontal layer. The template helps to get them aligned properly.
Some tips on cutting foil- I found it easiest to cut it with a paper cutter to get them straight and not too wrinkled, but I'm pretty sure this dulls the blade quickly. Decide for yourself what method works best for you. If you decide to use a paper cutter like mine you must cut very slowly or else the foil will tear and bunch up near the blade.
After you have enough strips, tape them as shown in the pictures. I would recommend wrapping them around to the other side and taping because these spots make fairly good contact points.
Step 3: Combine Layers
Although a fairly simple step, this took me a long time because mistakes along the way caused them to layers to not match up (even with templates). Basically, what you want to do is face the foil inward to the holes layer with the foil lines going different directions. Even though I warned myself not to, I accidentily arranged the foil the same direction (don't do it!) and had to fix it. You can see this point one of the pictures.
Step 4: Add Wires
Like I said before, use coated wire. Ignore what I did in the pictures.
Use the exposed contacts to get two sets of wires. This is where you will notice it was somewhat important to wrap around the foil as it makes a good contact point.
While soldering would normally be the expected choice for this kind of contact, we're working on paper so that isn't an option. I just slid the wires under the foil and tape (hadn't planned very far and covered foil there in tape) but you could juse tape the wires to bare foil.
Step 5: Connect and Test
Connect each set of wires to the two sets of inputs on your input device. I connected up a contact or two to the monome logic board and tested it out in 40h_serial.mxb in max/msp and it works! (believe me, by the end I wasn't so sure this would work and was surprised and delighted to find that it worked). If you used a keyboard chip just open up a word processor and if anything happens when you press a button, it works!
Hopefully with some foreknowledge your grid/keyboard won't be as ugly as mine, but even I can cover mine with some better paper or maybe rip apart a button membrane from a keyboard and use those for better tactile feedback.
Although it isn't shown in the images, adding dots where the holes/buttons are can obviously help dramatically.
Thanks for reading and if anyone makes one of these please show me, and even if you don't, please give some helpful feedback!