The LilyPad Electronic Platform is an electronic platform designed to be easily sewn into fabric using conductive thread, which provides designers freedom from the traditional construction method of soldering.
EL wire (electroluminescent wire) is a thin wire the glows when an AC voltage is applied. The wire is often wrapped in a colored transparent tube and is quite pliable. Many people often outline clothing (hats, pants, jackets, etc.) with EL wire, giving the garment an interesting colored glow. We, however, want to not only outline a garment but also control when the EL wire is lit.
Controlling the EL wire is not difficult but it does require some electronic pieces that everyday crafters may not be familiar with.
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Step 1: EL-Wire Difficulties
As mentioned before, the EL wire is only illuminated when an AC voltage is applied. Most, if not all, suppliers of EL wire also sell inverters necessary for this task. The inverter has a DC input and an AC output.
This is the beginning of our problem: how can we use the LilyPad to turn the EL wire on and off if the EL wire is controlled by an AC signal and the LilyPad uses DC? And the problem is often even more difficult, because the LilyPad board can be powered between 2.7-5.5 V. Inverters often have input DC voltages of 1.5V, 3.0V, and 12V, though input voltages range between 1.5V and 18V. Furthermore, if there is a spike or surge with the inverter it may damage the LilyPad.
Step 2: Optoisolator
First, let's tackle the voltage issue. Ideally, we would like to isolate the inverter and its power supply from the LilyPad and its power supply. That way, any surges in the AC line will stay on the EL wire side.
Luckily, good electrical engineers invented the optoisolator. Simply put, the optoisolator uses an IR LED to send an photon to a detector to control other side of the circuit. I used an NTE3044, which is an optoisolator with a Darlington pair. The Darlington pair is just two transistors in series.
If we connect the anode to a pin on the LilyPad, the cathode to GND of the LilyPad, and the collector to the Plus side of the inverter power supply, then we have effectively isolated the LilyPad from any dangerous spikes. The emitter will used as the trigger for the Triac.
Step 3: Triac
A triac is solid state device which allows for control over AC loads. If you apply a voltage at the Gate (G) relative to MT1 the triac will conduct from MT1 to MT2 as long as the current through the triac doesn't dip below a threshold hold value. I am using a MAC-97A triac which has a holding current of 5mA and a gate voltage of 2.0 V.
Every time I send a signal from the LilyPad to the optoisolator, that pulse is translated to a 2V pulse from the Darlington Pair. That pulse then opens the gate and grounds one side of the EL wire. That's okay, because we are going to connect the copper core directly to inverter. If you hold one line of the EL wire at GND and the other line receives the AC signal, the EL wire will still work because the AC signal will still be oscillating relative to something--in this case, the GND of the battery.
Step 4: EL Wire
There are a number of Instructables dealing with the stripping, prepping, and soldering of EL wire. This is my favorite. I stripped off the blue plastic from the EL wire, revealing a copper core and a smaller clear plastic tube housing the angel wire. After carefully removing the clear plastic tube I glued some copper tape to the EL wire and soldered the angel wire to the copper tape. If I had some shrink wrap tubing I would have inserted that over the copper tape for protection.
After soldering test that the EL wire illuminate when connected directly to the inverter and the inverter is powered by the appropriate source.
Step 5: Electronic Parts
- perf board
- soldering iron
- 330 Ohm Resistor
- NTE3044 Optoisolator Darlington Pair
- 6 or 8 pin socket
- Triac MAC-97A4
- 2xAA holder with 9V plug adapter
- jumper wires
Step 6: Solder Components
Before soldering it's always a good idea to lay out your components on the board and see how they will fit together. I made a number of mistakes and had to solder on jumper wires.
Notes: I curled up one end of the resistor so that I could sew from a pin on the LilyPad to the resistor.
A cartoon diagram is provided below. I soldered the DC inputs of the inverter to the resistor, triac, socket, power supply connecter, and two jumper wires: one for the minus side of the LilyPad and one for the copper tape on the EL wire.
I will provide an eagle file soon.
Step 7: Sewing and Soldering EL-Wire
- LilyPad Power Supply
- Conductive Thread
- El Wire
First decide on where the EL wire is going to be attached. We decided to simply outline the button of dress with the EL wire. Next sew the Lilypad and Power Supply to one another on the dress. Attach the perfboard with components, 3V power supply, and inverter to the dress (I used sticky back velcro). Lastly, solder the EL wire copper core to one side of the inverter and the angel wire to the jumper from the perfboard.
Step 8: Testing and Finish
Once everything is connected, upload a simple code that pulses a pin on the LilyPad HIGH and LOW every 2 seconds. If the EL wire doesn't flash, first check that the voltage from the optoisolator's emitter pin is between 2-3 volts. If it's still not working double check that the EL wire is illuminated when connected directly to the inverter.
When it's done, you'll be able to control the flashing of the EL wire!
This material is based upon work supported by the National Science Foundation under Grant No. 0855886. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.
Finalist in the
EL wire contest