I am an experienced sewer but had never worked with LEDs or electrical circuits before. I'm still bitter that I was forced to take Home Ec in high school, but was not allowed to take shop class. I could not find any instructions on the web that answered by very basic questions, so I've written this Instructable with others like me in mind.
Basically, I built the circuit, placed the LEDs into holes in a vinyl strip, and then covered the back of the strip with Velcro (TM). I sewed the other side of the Velcro onto the pants, pulled the wires out the top of the LED strip, connected them to a 9-volt battery and stuck the battery in the front pocket.
Be sure to review the circuit diagram for an overview of what's to come!
Step 1: Materials
Pants - be sure there are no pockets covering the side seams
1/4 yard vinyl - pick a color that matches the pants or consider getting a shiny silver vinyl to act as a reflector for your LEDs. Here is one example (scroll to the bottom of the page)
2 yards 2" wide sew-on (Non-adhesive) Velcro (TM)
1/4 yard woven cotton fabric- any color will do, I used a medium weight black
22 gauge stranded wire - this is from Radio Shack .
I got 22 gauge because that's all they had. I got stranded wire instead of solid since it's less rigid.
30 LEDs of your choice - I got these ultra-bright white LEDs because I wanted as much light as possible.
Two 9-volt batteries
Wire stripper and wire cutter
Single-edge razor blade
Rotary punch - available at sewing, crafts, and leather stores. You can use pretty much any tool that will cut 5 mm holes in the vinyl.
Soldering iron or gun
Cutting board - I used this old cutting board as a work surface when soldering.
Webpage to calculate the size resistors and batteries you'll need LED Series/Parallel Array Wizard
Appropriate resistors for your circuit - I used six 82 ohm 1/4 volt resistors and one 220 ohm 1/4 volt resistor in each circuit (for a total of twelve 82 ohm resistors and two 220 ohm resistors). Radio Shack does not carry these exact resistors so I bought these on-line. If you can't find the right ohm resistor, go up to the next one. Do not use a resistor with too little resistance because you could blow out the LEDs.
Yardstick or tape measure
Step 2: Planning the Circuit and the Placement of the LED Strip
Pick the specific LEDs you want. Go to the on-line circuit calculator of your choice. You will need to know the voltage of the LEDs, otherwise known as the "diode forward voltage". You will also need to know the voltage of the battery(ies) you'd like to use (the source voltage). I chose a 9 volt battery because it's compact and easy to slip into the pants pocket. I didn't need all 9 volts for the circuit and could have used four 1.5 volt AA batteries - but I didn't want the bulk of four batteries. Most LEDs have a "diode forward current" of 20 milliamps and that's the value I used.
Because I chose an odd number of LEDs, the circuit that dissipated the lowest wattage was a combined series/parallel circuit. I thought it was worth it to have the circuit generate as little heat as possible, so I chose that circuit rather than an easier parallel circuit. I had no idea how to actually wire the circuit and that caused the most difficulty I encountered in this project. So choose an even number of LEDs!
Review the pdf of the circuit diagram I used - the first circuit diagram is my complex circuit with both parallel and series components. The second circuit diagram shows the easier parallel circuit. If this is all Greek to you, look at the Instructable on parallel and series circuits.
Step 3: Prepare the Vinyl Strips
Cut two pieces of vinyl, each 4 inches wide and 2-3 inches longer than the leg measurement. The final strips will be cut down to their final size once everything is in place.
Mark the back of the vinyl with the location of each LED - be sure to center these on the strip.
Cut round holes on your marks. I used the largest setting on the rotary punch. It appears to be a 1/8 Inch punch, which the 5 mm LEDs fit into nicely.
Step 4: Wire the Circuit
Use a work surface that is large enough to support the length of the vinyl strip - this makes it easier to keep everything in place as you work. You'll want to first make the circuit with mechanical connections - no solder yet. At each connection, twist the wire or leg coming from the resistor or the LED around each other.
Lay the vinyl strip on your work surface and use it as a guide for placement of all parts. I started wiring at the bottom of the strip for no particular reason, but I think it makes sense to work from one end to the other so you keep one perspective on the positive and negative ends of the LEDs and the wiring. As you work, insert the LEDs into the appropriate holes in the vinyl strip. This helps stabilize the circuit and it ensures correct placement of the resistors and LEDs.
Long Red Wire
I considered the parallel part of the circuit to be the backbone, so I started by cutting one long red wire for the positive side of the parallel circuit. This should be about a foot longer than the vinyl strip so that you can connect it to the battery and have enough slack to drop the battery into the bottom of the pants front pocket.
I connected the 270 ohm resistor to the bottom of the red wire. It doesn't matter which end of the resistor you connect. I wrapped the bald wire around the leg of the resistor and then wrapped the remaining portion of the resistor leg around the wire. This results in a good mechanical connection which doesn't easily come apart. Use the needle-nose pliers to wrap the wires and legs - it makes it much easier.
I then connected the other end of the resistor to the positive lead of an LED using the same method of twisting the resistor leg around the LED leg and vice versa. Generally, the longer leg on an LED is the positive lead. You can check this by looking at the LED closely. The smaller plate is the positive plate. You have to get this right for the circuit to work.
Next, I connected the first of the six series circuits of my complete circuit. Since each of the series circuits used two LEDs, I skipped one LED hole and prepared the long red wire for the next connection.
I needed to remove the insulation from a short section of the red wire (about 1/2 inch long). Placing the red wire close to the holes in the vinyl strip, I used the wire stripper to pierce the insulation at the top and bottom of that 1/2 inch section. I recommend you try this first on a scrap piece of wire so you know which portion of the wire stripper cuts through the insulation without also cutting the wire. Once I had pierced the top and bottom of the section to be stripped, I used the single-edged razor blade to slice through the insulation lengthwise. This was easier than I expected it to be - the razor blade slides between the individual wires of the stranded wire if you push too hard, so you don't have to be as careful as you do with the wire stripper. Pick at the insulation with you fingernail and pull it away. It may take a minute or two to get it all off, but I found that preferable to accidentally cutting the wire. (Note, if you inadvertently cut the wire when removing the insulation, just cut the wire, strip the insulation off the ends you just cut, and connect by twisting around each other. You can see one of these connections in the eight photo.
For the series circuit, I needed an 82 ohm resistor. I wrapped that leg around the bare wire I just exposed. Then, I connected the other leg of the resistor to the positive leg of an LED, just as before. I then connected the negative leg of this LED to the positive leg of the second LED in this series circuit.
I connected the remaining positive sections of the series circuits. This constitutes more than half of the work in mechanically connecting the circuit. Yay!
Long Black Wire
For the negative portion of the circuit, cut a piece of black wire the same length as the long red wire. Similarly to the red wire, place it next to the LEDs that are now sitting happily in their holes in the vinyl strip. Determine the right location to strip the insulation off the black wire so you can wrap the negative ends of the LEDs around the bare wire to complete the negative part of the circuit. Wrap the negative LED legs around the bare wire.
Note for my complex circuit with combined parallel and series portions, only every other LED connects to the black wire. The remaining LEDs connect to the red wire. If you are smart and choose an even number of LEDs, you'll have a straightforward parallel circuit that looks like a ladder and every negative LED leg will connect to the black wire.
Last, connect the red and black wires to the 9 volt battery snap connector. Strip the insulation off the ends of the snap connector wires and the red and black wires. Note that the wires on the snap connector may be a different gauge, so you may need to use a different portion of the wire stripper to avoid cutting through the wire.
Test the circuit
You should now have a complete circuit connected mechanically! Turn the vinyl strip over and check the LEDs to make sure you've got the positive end correctly positioned. Trust me, even though I thought I was being careful, I still got two connected backwards. Since you haven't soldered the circuit it, it's easy to fix any errors. Now it's time to try it out and hope it works. Strip the insulation off the ends of the tops of the red and black wires. Touch the red wire to the positive end of the battery and the black wire to the other end. Your lights should come on. If not, check your connections to make sure they are good and check the polarity of the LEDs again.
Whew! I can't tell you how happy I was when I finally got my circuit to work. As I mentioned, I'd never wired a circuit before, so it took about 5 attempts before I got it right. I'm hoping this Instructable will help you avoid that frustration.
Step 5: Solder!
If you've never soldered, take a look at the [https://www.instructables.com/id/How-to-solder// How to Solder] Instructable.
Solder every mechanical connection you've made.
Wrap electrical tape around the wire-to-wire connections - this will be the connections to the battery snap connector and any patches you've made on the long red and black wires.
Step 6: Attach Backing to Vinyl Strip
I chose to hold the wiring, resistors, and LEDs in place with duct tape. I don't know if this will do any good, but I'm hoping it will help keep everything in place and minimize the chances the circuit will break in use. I also used a small piece to hold the top ends of the red and black wires in place.
Prepare the fabric strip
Cut two strips of fabric - these will serve as the base for the Velcro. Since the duct tape was 2 inches wide, I cut the fabric 2 3/4 inches wide, leaving room for a 1/4 inch hem on each side and room for the fabric to have 1/8 inch beyond the duct tape. This is to protect your sewing machine - you don't want the needle to pass through the adhesive from the tape. The fabric should cover the wiring plus 1/2 inch at the bottom and 1/2 inch at the top.
Turn over each side of the fabric 1/4 inch and stitch in place to create the hems. Check to make sure it will cover the entire circuit plus the 1/2 inch at top and bottom.
Sew on the Velcro
Stitch the prickly half of the Velcro to the right side of the fabric. This allows the soft side to go on the pants, which I think is nicer. I had 3/4 inch Velcro handy for the first leg and then bought some 2 inch Velcro for the second leg, so I have pictures of both. Both sizes work, just be sure you've got Velcro at the outer edges of the fabric strip for greater strength.
Sew the Velcro strip onto the vinyl strip
Stitch the Velcro strip to the back of the vinyl strip. Be careful to center it over the wiring and make sure the edges are clear of the duct tape. Note that the vinyl will be wider and longer than the Velcro strip. Stitch the sides first and then the bottom. Next, remove the small piece of duct tape holding the top ends of the red and black wires in place. Carefully hold them at the center of the strip while sewing the left top of the Velcro strip to the vinyl. Repeat for the right top.
The LEDs strips are complete!
Step 7: Sew Velcro Onto Pants
This is a little tricky since the pants leg is narrow, you have to keep pulling the other side of the leg out from under the presser foot of the sewing machine. I did this in two parts - I started at the top of the pocket and sewed as far as I could and then turned the pants upside down and started from the bottom. I was able to stitch the entire length of the Velcro this way.
I did leave the area over the knee without Velcro. My theory is that the knee moves the most when you walk, so I thought if the LED strip was loose over the knee, it might protect it from breaking from the movement.