This project was created for a class of mine: my professor of an FPGA design course offered extra credit to those who came to class dressed in a costume on Halloween. As a cliche engineer, I am terribly introverted and did not like dressing in costumes too much; however I still wanted extra credit. I thought it would be great to make my costume hidden from plain sight, then at any given moment I could control the output.
From there, I started my design on a discreet costume that was inspired from recent material that was covered in this class: SR Latches.
- For the project to be inexpensive
- To make the costume unnoticeable to most when not turned on
- To control the output of the costume in some mysterious way
SR Latches, or flip-flops, are a pervasive form of computer memory. They consist of two NOR gates (NANDs can be used as well), where their outputs are wired into each others' inputs There is also a SET and RESET input to the NORs.
To see how this SR Latch works, see picture 2. Let us first assume that Q is high and NOT Q is low. At this point, the SR Latch is considered to be in "Set State". During this moment, SET and RESET are both low. Q feeds into the lower NOR with S, which outputs low to NOT Q. NOT Q feeds into the higher NOR with RESET. Two lows NORed together output a high to Q and the so it stays. You can see that without doing anything to RESET or SET, the flip flop persists the value of Q. Follow the picture if RESET was brought high and SET stayed low. Q would go low and NOT Q would go high. Bring RESET back down to low. Q will persist in its low state.
To emulate this SR Latch, a 555 Timer is used. A 555 Timer is an adorable little IC created by Texas Instruments that can be wired in various ways for various functions. One relevant function is known as "Bi-Stable Mode". In this mode, the 555 Timer is connected to 2 buttons (called Trigger and Reset) with 1 output. When the Trigger button goes low, the output goes high and stays high. When the Reset button goes low, output goes low and stays low. Sounds like a SR Latch, doesn't it?
If you are interested in more about the 555 Timer, visit: https://www.instructables.com/id/555-Timer/ which is where I learned about the 555 Timer.
Step 1: Parts/Tools and Cost
The parts listed is simply what I used and many of them can be swapped with other parts.
Parts; Quantities in ( )
- (1) EL Wire - Blue 3m -- https://www.sparkfun.com/products/10195
- (1) EL Inverter - 3V -- https://www.sparkfun.com/products/10201
- (1) LM555 Timer -- https://www.sparkfun.com/products/9273
- (5) 10K ohm resistor -- Radioshack
- (1) 470 ohm resistor -- Radioshack
- (1) LM7805 Voltage Regulator -- Radioshack
- (1) Small PCB board -- Radioshack
- (1) 0.01 micro Farad Capacitor -- Radioshack
- (1) 6 Volt battery, preferably over 1 AmpH -- BatteryPlus
- (1) NPN Transistor -- Radioshack
- (1) Spool of speaker wire -- Radioshack
- (Some) Wood, for the box -- Tree
- (2) Small push button -- https://www.sparkfun.com/products/9190
- (2) Servo horns -- Leftover servos
- (1) Shirt of your choice, thinner is better
- (1) Spool of matching thread
- (1) Strip of velcro, both hooks and loops
No special tools were used: soldering iron, helping hands, hot glue gun, power saw and pliers.
If you have to buy everything, it will probably cost you around $50 to $60.
Step 2: The Circuit Diagram
The circuit used for this project is really straight forward. Many would likely criticize me that I didn't use decoupling capacitors for the LM7805 voltage regulator. This is for 2 reasons: for one, I didn't have any on hand, and since it's just a Halloween costume, I didn't find it necessary to get any; and second: the EL Inverter will happily run on anywhere from 2.7 volts to 4.2 volts, so I didn't care too much about ripple.
Observe the LM555 Timer, its output is connected to the Base of an NPN transistor. When I press the Trigger button, the output goes high and the transistor connects the GND pin of the Inverter to Ground, and thus completing the circuit. At this point the EL wire will glow. If I were to then press the Reset button, the output on the LM555 goes low and the transistor disconnects GND from ground so the EL wire turns off.
Looking at the LM7805 voltage regulator, I added two resistors to adjust the voltage output. The 7805 will originally output 5 volts, but with the resistors positioned as such, with their values will reduce the 5 volts to about 4 volts. There are "Adjustable" voltage regulators sold at Radioshack for about a dollar more; however these seem like a scam to me since any linear voltage regulator can be adjusted in this fashion (at least to my knowledge, there might be one where this doesn't work). Adjusting the ohm values of these resistors will adjust the output voltage.
The LM7805 can only handle up to an Amp of current, so you won't be able to wire a bunch of EL Inverters in parallel to it.
The 6 volts goes straight to the LM555 because the 555 Timer needs to have 4.5 volts to 15 volts.
Step 3: Building the Linear Voltage Regulator Circuit
Here you can see the prototype circuit wired up on the bread board. When adjusting the voltage out with the resistors, I guess and checked the values until I got 4 volts out. While I was constructing my circuit, I only had 10K and 470 ohm resistors on hand. To get the voltage I wanted, I had to put two 10K and one 470 in series to connect the ground pin of the LM7805 to ground. I used one 10 K in between ground and the voltage out.
In the first picture, I have it all connected and the wire is glowing. It is not easy to see it glow in bright light so the second picture shows its brightness with the lights off.
In the 3rd picture, I marked the PCB on where to cut. The largest portion will be used for the 555 timer and voltage regulator. The two smaller pieces will be used to mount the buttons onto. When cutting this, I use Diagonal cutters. Be prepared for the smaller PCB pieces to want to shatter. Just be careful cutting the board and if the smaller pieces do shatter, don't worry: the smaller pieces only need to be big enough to mount the button onto.
After verifying the voltage regulator circuit, I started soldering the pieces onto the PCB. See the circuit diagram for a reference. To interface the EL Inverter to the PCB, I soldered 2 header pins for it to plug into. Be sure to not solder a header pin directly to ground because it needs to connect to the Collector pin of the transistor. For the battery, I soldered wires directly into the board.
Step 4: Construct the 555 Timer Circuit
Wire the 555 Timer into your breadboard for Bi-Stable mode to be sure you have it right. See the below video for a demonstration for how it will behave:
Now that you verified its functionality, replace the LED and 470 resistor with an NPN transistor. Connect the output to the Base of the transistor. Wire one leg of the transistor into the GND of the Inverter and the other leg goes to ground.
Connect the PCB to the breadboard to regulate the voltage going into the Inverter. Use the circuit diagram as your guide.
The below video will demonstrate the operation:
After I confirmed the operation of the 555 Timer, I soldered all the pieces to the PCB. After I finished, I found the soldering to be a bit precarious and in risk of shorting, so I took a hot glue gun and glued everything into place. This preserves the integrity of the connections and keeps the board from accidently shorting on anything.
Step 5: Making a Simple Box
I made a simple enclosure to protect the project. With a small flat of wood, I drew some lines where I would like to cut to build the box. It's not a full enclosure, because I didn't want to put an effort just to make a lid for a Halloween costume. I wanted something simple and easily accessible without too much work. All the cuts were made with a power saw.
After I made all the cuts, I nailed the Inverter to the bottom piece of wood for the box. The ends of the nails were snipped and filed down. The velcro was used to hold the battery into place.
On one of the long side pieces, I drilled a hole for a switch to fit through. I bolted that on. This will connect and cut off ground from the battery.
To be simple, I taped the board to the battery with electrical tape. It's a surprisingly strong fit.
Solder the switch in, and make the connections with the Inverter. Now you will need to glue all the pieces together. I used wood glue and used C-clamps to hold the box together while it dried.
Since I would be wearing a black shirt and dark jeans, I painted the box black to try to hide it.
Step 6: Sew the EL Wire Underneath
I made a really simply design as featured in the main picture. The start of the EL wire would be at my left hip and end at my right hip. The EL wire would be threaded to conform to the design pictured; it also moves over my shoulders.
Since this is my first time with EL wire and sewing, I realized I would have to be flexible for myself. I decided I would sew the start and end first, and leave the back design up in the air for whatever wire I had left (I knew I would have some left over after the front).
Some Thoughts on Interfacing EL wire to Fabric
Here is where my project differs from others with EL wire. I wanted the EL wire to be underneath my shirt so it wouldn't be visible and in turn, I have been able to fool many people thinking I was not wearing a costume at all.
For much more comprehensive information on interfacing EL wire to your garments, check out this article:
In this article, it is suggested that you use a thick fabric, for instance: leather, and to not use a thin fabric: for instance: a t-shirt. The reason for this is because the wire will want to flex the fabric if the fabric is thin.
With my project, I am using a thin black t-shirt anyway because the EL wire needs to be visible through the cloth.
First I put the shirt and used pins to mark the underline of my chest to match my design. Then I carefully removed the shirt and turned it inside out so I could sew to the inside.
To sew the EL wire to my shirt, I placed small squares of tape onto the wire and used a pin to hold into place. I would then sew through the tape and shirt to hold it in place. In retrospect, hot glue may have been a better option; however, with how thin the shirt is, the glue may have seeped through and be visible. Sewing the wire on is also pretty durable.
For the tape, alternate between using masking tape and electrical tape. The wire is bright enough to glow through the masking tape but is cut off from the electrical tape. The electrical tape creates the "broken wire" effect.
However, you must be careful to not sew too tightly or you'll get these snags in the fabric. These are not very appealing. Simply take your time. This took me a solid five hours to complete. If you look at my pictures, it's difficult to see any wire underneath my shirt.
After I finished sewing, I needed to work on the buttons. The buttons I purchased originally are really difficult to press because how small they are. I solved this by super gluing leftover servo horns to the buttons. This makes it really easy to trip the button.
Sew the push buttons onto the underside of the ends of the sleeves. I did this so I could close the button by pumping my arm. This amazes many people due to there being no apparent way that the circuit is being controlled; leading most people to ask: "how did you do that?"
Step 7: Finished Product
I was very happy with my project. It's very subtle and I was successful in amusing my classmates and friends with it. In addition I got the extra credit in my class.