The main reason for this project is to interface it with a multitouch table setup without going through the hassle of setting up an Infrared light pane. (See NUI group for more information.) Essentially, to get a finger recognition software to detect the LED lights as fingertip inputs.
you can just build it for fun :)
Step 1: Materials & Tools
* 3v coin battery (I use model C2032)
* LEDs (Choose depending on application or personal preference)
* Scrap plastic sheet (can be from packaging)
* Scrap aluminum sheets (can be from a softdrink can)
* A pair of earphones (preferably one you wouldn't miss)
* Conductive tape
* Wrist strap
* Soldering kit
* Rotary kit
* Digital Multimeter (Optional)
* Sand paper/bits
* Hot glue/glue
* Clear Tape
Step 2: Design the LED Circuit Layout
a. Decide how many and what kind of LEDs you want to use. I used three 3mm orange LEDs
b. Calculate how much resistance you need with a 3V power (from the coin battery). I used this online LED calculator.
c. Determine the length of your wires. Measure out how long of a wire you would need for each of your fingers. Allow for extra room for bending and wire cutting mistakes.
a. To make it easier to work with two hands you can use a transparent vinyl glove as an aid. Just slip on the glove and draw out where everything should go on the glove. Now you can use the glove to measure out the length of the wires.
b. For my application, I need LEDs with light in the range of infrared or close to infrared. I tested with my modified camera (that has a 850nm bandpass filter) and confirmed that it can see LEDs of colors red, orange, and yellow in addition to 850nm IR.
c. You can use alternative wires instead of earphone wires but I find earphone wires to be compact (each wire already has 2 strands) and flexible. Alternatively, you can use conductive threads and sew them onto a glove.
Step 3: Strip and Join Earphone Wires
In my case, I am only planning on building a three-fingers setup so I cut three pieces of wires (one for each fingers). One one end of the wires I joined the three positive strands together and the three negative strands together to create two main strands. (You can arbitrarily determine which color is the positive strand and just stick with it.) The other end of the earphone wires I just left it with two strands coming out each end to be connected to the finger piece later.
a. Cut and strip wires
b. Burn wire ends to remove fibers inside the wires.
c. Sand away the non-conductive coatings at the wire tips.
d. Twist and connect the positive wires together at one end; do the same for the negative wires. Leave the wire ends going to the fingers loose.
You can test to see if the wires have shorted or is working properly by using a multimeter on a continuity setting. Touch the ends of the probes to the ends of the wires. The multimeter will emit a beep when there's current flowing through from end to end.
Step 4: Build Coin Battery Holder
a. Using a piece of aluminum sheet with non-conductive coating, bend it to encase a coin battery. Leave one side open for the case cover.
b. Make a battery case cover from a piece of scrap plastic and adhere two pieces of conductive tape. make sure one of the conductive tape will touch the positive terminal and the other will touch the negative terminal of the battery. We will be soldering the earphone wires to these conductive tapes.
c. Connect the case to a wrist strap. (I used old watch strap and a bit of fishing line to hold it in place.)
To make an aluminum sheet non-conductive just sandwich it between transparent packing tape. To make conductive tape, you can use strips of aluminum foils strengthened with tape. (but I heard they are hard to solder to)
Step 5: Build the LED Casing/Finger End Piece
In my case, I used a piece of aluminum strip coiled around my fingertip to act as both a conductor of the negative current and structural support. I will touch the cathode leg (-) of the LED. For the positive current I used conductive tape and a resistor to connect the anode leg (+) to the earphone positive strand.
a. Cut acrylic to finger size.
b. Drill a hole in acrylic to house the LEDs
c. File down LED if it is too tall for the acrylic thickness.
d. Tape two pieces of conductive tape to one side of the acrylic. (these will be the positive and negative contacts)
e. Put LED in the acrylic and bend the legs. Each touching a piece of the conductive tapes.
f. Solder the LED legs onto the conductive tapes.
g. Solder a resistor to one of the conductive tapes.
h. Trim off excess LED legs
i. Hot glue aluminum coil to the acrylic
Make sure to the keep the positive side and the negative side separate on the finger piece. Use clear tape on the aluminum strip if you have to.
Step 6: Solder Everything Together and Test
a. Use solder or conductive tape to connect the finger piece to the earphone wire strands.
b. Solder the wire strands to the coin battery casing cover (the piece with conductive tapes)
c. Slip on the finger end piece and use your finger tips to push the aluminum strip together with the exposed LED terminal. The LED should light up.
To avoid the wires going all over the place you can cut some coils and make finger rings out of them and slip the wires under the ring.
Using it with Multitouch Setup
Start up Core Community Vision or Reactivision and adjust the camera sensitivity till you can see each lighted LED as a finger input. You may wish to cover the acrylic finger piece with something softer so it doesn't scratch your surface.