Have you ever noticed that almost all baseball caps are ready-made for inserting LED's? Why don't cap manufacturers just go ahead and insert 3-mm LED's into the 6 threaded grommet holes (eyelets) in the top of the hat? After all, besides the LED ports, each cap also comes equipped with 6 seams to serve as insulated conduits for running wire or conductive thread. Moreover, the 1-inch head band running around the inside base of the cap provides a perfect slot for hiding a button battery and associated circuitry.

Not to worry! This Instructable describes how to add the six LED's that the cap manufacturers evidently forgot to install. The project features the "thin" LED blinky circuitry available from SparkFun, namely the programmable LilyTiny chip. But no programming is required for this keep-it-simple introductory electronic wearables project.

OK football fans, I know the Ravens just knocked the Steelers out of the Super Bowl playoffs. That just means I gave someone else a chance to try out this project with your favorite team cap.

Supplies

Pittsburgh Steelers Baseball-style cap - fitted (Amazon.com)

6 x 3-mm Clear Yellow "NightFire" LED's (Amazon.com)

CR2032 3-volt Button Battery and Sewable Battery Holder (SparkFun)

LilyTiny Sewable Blinky Chip (SparkFun.com)

LilyPad Sewable On/Off Switch (SparkFun.com)

Conductive Steel Thread and Needles (SparkFun.com)

Felt Padding Material (SparkFun.com)

24-Gauge wiring

NOTE: All of the SparkFun supplies used in this project came with the LilyPad Design Kit.

Step 1: Layout and Wiring Diagram

As shown, this is a "hybrid" project combining wearables components (conductive thread style) with traditional electronics parts and wire. Conductive thread is used for the concentric positive and negative rings in the top of the cap. It is also used to create a flexible hinge at the head band, which allows the head band to bend down freely for flipping the ON/OFF switch and battery changing.

It is possible to use 100% conductive thread, but this turns out to be somewhat challenging to avoid shorts with all the curves, flaps, and connections in the cap.

The project also features the use of the SparkFun LilyTiny mini-board to provide a simple ON/OFF Blinky function. The LilyTiny consists of a surface-mounted 8-pin ATTiny chip, and perhaps provides the smallest and thinnest blinky function circuit readily available. The LilyTiny takes a Positive and Negative input from the battery and then outputs a pre-programmed ON/OFF blinky signal from its Port No.2. The other Ports (1,3,4) give different styles of blinking (Heartbeat, fade, etc) which are not used in the current project. Advanced users can re-program the ATTiny chip to customize the blinking functions.

One design goal is thinness and smallness. So I have used a non-switched CR2032 3-volt battery holder because the switched version is too big. Thus I have soldered the LilyPad ON/OFF switch onto the Port No.2 of the LilyTiny board (shown later). I also filed down the battery holder's excess board a little bit to reduce the height to <1-inch.

Step 2: Select and Test Your LED's

I am using bright, clear, 3-mm yellow NightFire LED's that have a beautiful golden color. I had concluded from an earlier cap design (Washington Nationals) that the diffused red 3-mm LED's were a bit too dull.

Those with LED skills will recognize my baseball cap circuit as a modified LED "throwie" with 6 LED's powered by one 3-volt CR2032 button battery. Therefore, the first test is a simple 6-LED throwie (as shown above).

Since we are only using one small battery, the goal is adequate brightness without any apparent heating of the parts. Another goal is reasonable battery life - hopefully at least long enough for the big game. The final circuit should have longer battery life than this throwie mini-test due to the added ON/OFF blinking function and additional circuit resistance including the conductive thread.

Re: LED Size - it turns out to be the smaller 3-mm LED size that fits in to the threaded eyelets from the underside of the cap. The smaller 3-mm LED's are also practical and somewhat subtle. When turned-off, the cap can be used as a regular cap and no one would notice the difference. Ultimately however the goal is a decent light show, so I personally wouldn't shy away from trying a giant 10-mm gumball LED inserted from above the cap.

SAFETY NOTE: Those experienced with LED's know that different types, sizes, and colors of LED's can have different battery and circuit requirements (resistors, etc). Therefore selecting a different LED may require some re-assessment of the simple circuit I am providing in this Instructable.

Step 3: Pick a Sports Cap

Almost any baseball-cap can be used for this project. We are looking for the standard 6-segment cap with 6 threaded eyelets. They typically have 6 seams running from the top to the bottom the hat, which can be used as wiring conduits. There is a nominal 1-inch head band with a cuff so you can inert wires and components behind the cuff. The head band also has seams so you can run wires through those seams too.

Fitted caps in your exact head size (eg; S, M, L, XL) are the easiest to work with because the head band cuff goes all the way around the entire cap without interruption. But one-size-fits-all caps can probably be used with adequate planning. I used a 47 Brand official NFL fitted Steelers cap.

The only other thing to watch out for is excessive embroidery for team logos etc. which can obstruct some the seams you may be planning to run wires through.

Obviously you want to pick a cap color scheme that looks good with your selected LED color.

Step 4: Prepare LED's and Insert Into the Cap

The idea is that the 3-mm LED's are inserted from the underside of the cap into the cap's threaded eyelets. As shown, the legs of the LED are bent straight out. My technique (re: conductive thread) is to use needle nose pliers to create an eye loop at each end of the LED lead. Then I solder this eye loop closed to prevent the thread from escaping the eye loop.

Insert the LED's into the cap with the positive side pointing to the top of the cap. Sometimes the 3-mm LED's fit snugly and sometimes the fit is a little loose. Use a piece of electrical tape behind the LED to help hold them into the cap holes.

Alternately, fabric glue might be used to hold the LED's in place. But that would be a final step. You will be doing a lot of manipulation to the hat during wiring, so any glue applied at this point will probably not hold.

Step 5: Use Conductive Thread to Wire the LED's

Before you start wiring, check to make sure you installed the LED's correctly using a button battery. LED's only light up when wired correctly (re: positive and negative sides).

Firstly, note that we need to connect the conductive thread to the 24-Gauge lead wires as well as the LEDs. Therefore snake your positive and negative lead wires up the appropriate seam. I am placing these wires inside the seam, which is a little tricky but not too hard. Now just like the LEDs, make a soldered eye loop at the ends of the lead wires. The top lead wire eye loops are a little special: if you make them thin enough, you can pull it back into the seam to hide the thread connections and frays you are about to make.

Now you are ready to do some sewing with conductive thread. My sewing technique is double-thread sewing and I make 3 or 4 loops around each eye loop to make sure I have a good connection.

Start by tying a knot onto the lead wire eye loop, then make an anchor stitch through the fabric of the seam and then go the first LED, makes some wraps around the eye loop, make another anchor stitch at the next seam, and so on. Finally you will wrap around and tie off back at the lead wire to complete the circle.

You will have some loose ends and frays at the lead wire which can be treated with clear nail polish to prevent unraveling. But go easy on the nail polish with tiny amount at the knot.

Now if all went well, you can carefully pull that lead wire back into the seam, and all the knots and frays are hidden.

Makes two such threaded loops representing the positive and negative concentric rings, as per the Step-1 wiring diagram..

Step 6: Prepare and Install the Control Circuit

As shown the idea is to hold the electronics and battery behind the head band seam. The CR2032 battery holder is soldered by short wires to the LilyTiny and the ON/OFF switch is soldered directly on to the Port-2 on the LilyTiny.

Make sure the battery holder is positioned to allow easy removal of the battery. Make sure the switch is easy to reach. Make sure the polarity matches your positive and negative leads from the LED's. Try to locate the assembly where it does not bulge out the hat (avoid placing the battery holder at a spot where the band is already thick due to internal seams etc).

With reference to the Step-1 wiring diagram, run your positive and negative lead wires to the assembly and solder them into place. I first ran the lead wires under the seams of the head band.

The other end of the lead wires are then looped and soldered in preparation for conductive thread. As shown you should have two sets of two lead loops at each end of the cap, ready for connection with conductive thread. Using the same sewing technique, connect these loops with about 1.5-inches of spare thread to make a flexible hinge. This allows easy access to the battery and switch. I start at one loop, make a knot, then go to the next loop leaving slack, make some wraps, and then go back to the first loop, make some wraps and and tie off.

Flip the ON/OFF switch and pray for blinky lights! If all is good, go ahead and secure the assembly onto the cap head band by sewing with conventional thread. Since we have used sewable components, there are lots of spare holes to tie down the circuit assembly.

Step 7: Covering the Wires

You can wear the hat at this point, but to hold the LED's into place more securely and avoid getting your hair stuck in the wires, you will want to cover the inside top of the hat with felt.

Cut the felt into 6 triangle shapes and adhere with temporary spray adhesive. It's a 60 degree equilateral triangle.

You should be able to carefully hand-wash the cap, but first remove the battery. You will have to re-stick the felt.