A QWERTY – that’s how I have named it- is a device that works like a MakeyMakey (http://makeymakey.com/) but which is built upon an old keyboard and a few inexpensive elements. Actually, most of the materials used on its instructable may be reused or recycled.
Step 1: Some Theory Before Starting
A keyboard consists of switches -as many as keys- and an electronic board with an IC that translates the arriving information from the keys into a language that the computer can understand. The picture shows some switches and conducting paths on two plastic sheets. Paths are connected to the terminals of the electronics board on the other end.
As a key is pushed, both foils get in touch, thus closing the circuit and sending one signal towards the IC that talks to the computer.
The diagram of a keyboard could be simplified as avobe, wherein a momentary switch (key), two conductive wires connected with the terminals of the electronics circuit and the USB connector that links with the computer are present.
In order to transform the keyboard into a QWERTY we will need to add something else. That’s because, in case we used an object with a high resistance to connect both ends of the wire, the voltage fall would be so high that the IC would not get any signal.
This can be achieved by means of a transistor.
The transistor may act like a switch when some current is applied to the Base, which corresponds to the end being touched by the guy’s finger in the previous drawing.
One transistor that is able to close (drain) with a voltage as low as the resulting to pass 5V through our body is needed. I used NPN BC547N transistors for that purpose, but other types could work fine as well.
Step 2: Collect Materials
The list of materials has been divided in two sections: essential materials and optional materials. This is due to the fact that final design of the device will depend on your own imagination as well as on the materials you will be able to obtain.
- 1 old keyboard
- 6 transistors NPN type BC547B, with an aproximate cost of 0,05 $ each.
- 1 protoboard. One small piece is enough.
- 1 set of wires with alligator terminals.
- A few wires, preferably thin and in different colors. I took mines from a parallel comunication cable of an old printer.
- 4 screws 30x4 mm including their nuts.
- 4 spacers. I used small white plastic tubes instead.
- Policarbonate board
Step 3: Tools
- Soldering iron and wire
- soldering paste
- hand saw
- screw driver
- 4 mm drill
Step 4: Check the Keyboard
Most old weyboards use to have mechanical problems. If that’s your case, you can just go ahead because only the electronic board and the USB connection cable will be necessary.
Step 5: Dismantling the Keyboard
Together with the electronics board, inside the keyboard you will also find a couple of plastic layers with a lot of circuits printed on them. They actually connect each key with the board.
Some keyboards have circuits on one of the plastic layers that have some Volts, whereas circuits on the other layer are connected to ground. But another type of keyboards exists wherein both plastic layers have some Volts. However, the voltage level is higher in one of the two layers.
Let’s now focus on the electronics board.
Step 6: Mapping the Keyboard
We shall start numbering the pins and finding out which are the ones that connect with the keys that we want to use.
In this case we only will use four cursor arrows, space and return keys. Obviously, we can take as many keys as we want because over 100 keys are at our disposal on a keyboard.
Please take into account that the ENTER key does not work with Scratch. Therefore, if you are planning to use the QWERTY with scratch exclusively, you should map another key.
To find out the pins belonging to every key you have two options:
- Follow the conductive lines from the point until the pin connecting with the board.
- Use the continuity option from the multimeter: place one of the test leads on the round’s key you want to map and move the other one on the pins until you find the one that gives conductivity.
Before you start working on the next step, it’s advisable to test that the pin numbers you have found are right. In order to do that, you will only have to connect the keyboard’s board to the computer through the USB, open a text edition program (Word, for example), and connect both pins from each key with a cable. On the computer screen you should see the exactly what you wrote on the paper, otherwise you have to look for a bug.
Step 7: Ensambling the Transistors Board
Please consider that pins on the board with a certain voltage (or a higher voltage) should be connected to the transistor’s collector. In this case, pins with a voltage are numbered 3, 4 and 5 (second column on the previous step). But this might change depending on the keyboard you use.
Now it’s worth to spend some time thinking on the way to simplify the wiring between the electronic board and the transistors board. The use of cables with different color is really helpful. The hand made figure shows the cables that are connected to each terminal form the transistors.
The two pictures show the board seen from both sides. The wires that are to be soldered to the keyboard’s board are the ones on the bottom. The wires on the top will be used to drive our QWERTY.
Step 8: Linking Both Boards
Now we need to solder the seven cables on the bottom to the keyboard’s electronics board. To make it possible, in the present keyboard (see picture) it was necessary to scratch a layer of black material that was covering the copper pins.
It’s absolutely necessary to use welding paste in order to obtain good results.
We will extract the 5V+ from the keyboard’s board. We can take them from the end of the cable coming from the USB, which usually is red colored.
Step 9: Preparing the Frame
Now we will put everything together on a frame or in a box. There are many possibilities. Your choice will depend on the materials you can get and on your imagination. In this case we used two polycarbonate plates.
Above these lines you can see the drawing of my top plate. The bottom plate presents the same external dimensions and also 4 mm diameter holes on the corners.
The top plate is somewhat more complex because it comprises the sensible terminals where alligator clamps will be connected.
I did use a drill and a handsaw to construct the plates.
Terminals are constructed from a 10 cm long copper wire piece. The wire should be rolled around one of the hole pairs.
Add the tin wire which should be melted very carefully, otherwise you will melt the polycarbonate plate too. The result will be much better if you use soldering paste.
Now, you can draw the control signs on the back side of the polycarbonate plate.
The bottom plate is much easier to do because it does not have the holes for crocodile connectors. Only four screw holes are needed.
Step 10: Artwork
Once both plates are drilled and cut, you can ask a local artist to transform them into art.
Step 11: Ensambling All Parts
Now it’s time to do the connections on the back side of the top plate, according to the scheme you did before.
The electronics boards can now be fixed on the bottom plate.
Screw both plates together, using four small plastic tubes.
The USB cable can be fixed to one of the spacers, to avoid the effects of hitches.
You can use a drop of hot melt glue on each one of the bolts to protect the table from scratches.
Now your QWERTY is ready!
You only have to construct a Joystick with Play Doh, one banana or anything you find is barely conductive, and connect your QWERTY to the computer which will recognize it as a keyboard...