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Building Game-Show Controllers for You Don't Know Jack
Preparing the Keyboard
What You Need
- A cheap PC keyboard, such as the $10 "Fry's Special" (BJMT 104-Key "Perfect Touch Feeling" Windows '95 keyboard, #2294158)
- A screwdriver to take the keyboard apart with
- 26AWG stranded wire
- A soldering iron & solder
- A Dremel tool, or something else to grind away some plastic with
- A multimeter (analog or digital, preferably with a beeping continuity checker)
- 15-pin male VGA connector (Radio Shack cat. number 276-1501)
- Plastic "hood" for above, cat. number 276-1539
- Double-sided tape
There are so many brands of PC-compatible keyboards it's hard to give any guidelines to select one with. Most of them work the same way, though, so these instructions should be adequate to talk you through anything you find.
Remember, the goal of this part is to isolate the connections you need to bridge to mimic a keypress. When you're done with the keyboard, you'll have some labeled wires sticking out a hole in the back. Touch the right 2 wires together and it will be as if you pressed a button. Can you see how this is a good thing? You could make a lot of neat controls with this trick -- even customized control panels for your favorite flight sim.
2 Types of Keyboards: Microswitch and Membrane
Basically speaking there are 2 types of keyboards. The more expensive kind, which feel better, have tiny switches under each key cap. The cheaper kind uses, instead of switches, layers of of conductive stencils on plastic backing (see the photos). When you push a key, it presses 2 conductive "dots" on the layers together. In both cases, when the circuit is closed the keyboard sends a character to the computer. Chances are, if you have a really cheap keyboard, it uses these layers of plastic instead of microswitches.
This presents 2 problems. First, you can't solder to this plastic sheet with a conductive stencil on it. Second, it's hard to trace the circuit back to a place you can solder to. Fortunately there is a trick that makes this easy to solve. We'll look at that shortly.
Photo: Keyboard Overview
Chances are your keyboard will look a lot like the one above. There should be a circuit board with some exposed solder joints on it, as well as 2 layers of plastic with intricate circuit patterns on them. Each wire (not standard equipment!) in the photo above relates to a key, and each key needs 2 wires. So how do you figure out where to put those wires? That's the only hard part of this whole project. Keep reading.
Photo: Labeling the Layers
The very first thing you need to do is get a permanent marker and label the keys on the plastic. Make sure you label which plastic layer you are looking at, too. See above, how there are 2 sets of the numbers 1-4? You have to mark the keys you are interested in on each layer. Do this for 1, 2, 3, 4, p, b, q, and s. Double-check your labels before you go on.
Photo: Tracing Connections
OK, the picture above is one of the most important. It clearly shows a couple of important things. First, look at the membrane on the left. The brown-colored traces are not connected directly to the green circuit board. When the keyboard is assembled, the membranes are folded over such that their contacts (the vertical stripes right below the black stripes ) are pressed against the black contacts on the PCB -- pressure holds them there. As it is though, these is no connection between the membranes and the rest of the circuitry. Second, the black contacts on the PCB are connected through the traces to the solder blobs.
This means you cannot use a multimeter to look for a connection between the little dot under a key and one of the solder joints. No, finding your connections is a 2-step process. First, you need to use your multimeter to find which membrane contact is electrically connected to the "dot" for a key. Set your meter for resistance. If its not autoranging, set it to the 20-200 ohm range. If you have a "beep" continuity checker, don't use it, and here's why: there is too much resistance in those little brown traces to set off the continuity checker once you have a few inches between the probes. Whatever this stuff on the plastic is, it doesn't conduct as well as wire. You could see resistance of over 150 ohms from one end of the plastic sheet to the other. My continuity checker stops beeping at about 60 ohms.
Once your meter is set up, do this: touch one probe to a dot. Let's start with the dot for "b" on the first layer of plastic. Now, touch your other probe to the contacts on the plastic, up by the PCB. Only one will be connected to your dot; when you touch the probe to it, the needle will swing. Note your discovery. Repeat the procedure for all the other keys, for both layers of contacts.
Now, set your meter to "beep" on continuity. Check to see which bit of solder is connected to the black contact that corresponds to a key's contact on the plastic. These are the places you will solder wires to.
Take good notes! Sketch the contacts in front of you and write down which contact and which solder joint relates to which key as you discover it. Then, double-check it all. Believe me, you don't want to take they keyboard apart again.
Photo: Running wires
Solder wires to the solder joints you discovered were relevant, and use tape to label the ends of the wires. What numbering system you use just depends on how your keyboard is laid out. Use some duct tape to stick the wires down to the PCB. Use a Dremel tool or something similar to grind away a semicircle big enough to accomodate your bundle of wires, and run them outside the keyboard. When you are done, reassemble the keyboard.
When you solder, use lengths of wire about 8" long. The wire should be fine and stranded, of approximately 26AWG.
There are really a million ways you can work the connectors, but I recommend using a 15-pin VGA connector. If your keyboard has enough space inside, you could mount the VGA port in the plastic of the keyboard. I didn't have enough space, so I used double-sided tape to stick it to the underside of the keyboard.
At this point you have a port on a keyboard; if you short the right 2 pins together, it will be just as if you pressed a key. At this point you could make some buzz-in hand controllers, connect them right to the port, and be playing You Don't Know Jack, albeit without a big illuminated answer panel. Just use the keyboard for everything but buzzing in. Hand controllers are covered on the next page.
If you don't want to build the Console at all, you can almost stop here. Forget the VGA connector. Instead, you want to set 3 1/8" jacks into the keyboard itself, preferably somewhere near the front. Build 3 buzzers (described on the next page) and plug them directly into the keyboard. You're done!
You know, there are actually a lot of games that could benefit from a port like this on your keyboard. You could plug a foot pedal in to they keyboard this way, and use it in Quake 2 or any other game. Someday I intend to experiment with this.