My starting point was this instructable: https://www.instructables.com/id/Lightsaber-for-$33-in-33-minutes/
I modified the plans a bit to fit my own needs and came up with what you see above.
Once you have your own designed and built (there are many other fantastic guides besides the one I used), you'll need to get a few things. The current line of cheap Hasbro lightsabers actually have excellent sound. You could of course spend a little more on one of the really great custom boards available from The Custom Saber Shop, but the Hasbro one really is quite good for the price.
What you will need:
-Cheap Hasbro lightsaber with electronics (I used the 2010 Anakin saber that comes with the Clone Wars DVD)
-Momentary switch (this one from Radioshack fits nicely: http://www.radioshack.com/product/index.jsp?productId=2062508)
Tools you will need:
-Soldering Iron + wire
-Dremel or other rotary tool with cutting disk (can be done without, but makes parts of this much easier)
-Various screwdrivers, pliers, and a sharp knife
Once you've gathered your materials, we will gut the Hasbro lightsaber and then do some soldering to make everything fit nicely in the new saber. Although you need to be able to solder for this tutorial, that's about the extent of the work you need to do with the electronics. Besides wiring the new switch, all we need to do with the electronics is solder extensions onto the existing wires. For the most part, you don't have to worry about messing anything up if you're still getting the hang of soldering. You will need to be very careful, though, when we briefly solder a connection to the circuit.
Step 1: Modified Saber: Gutting the Donor Saber
My biggest fear when taking the Hasbro lightsaber apart was damaging the circuit. I'll show you exactly where to cut in order to minimize the risk of damage. By the way, when you open everything up, you might consider marking the wires before cutting them. In my experience messing with the board, the polarity didn't seem to matter for the speaker and swing sensor, but it may be better to be cautious.
1) Remove all screws
Are you ready to void the warranty? Great. There were only a few screws on the outside of the Anakin saber. Take em all out.
2) Cut off the base of the hilt
You won't have to worry about damaging anything if you just cut straight through the hilt at the head of this base section. You can use either the hacksaw or the Dremel. You will probably sever the wires, but we'll need to do that anyway. Keep this part of the lightsaber handy because in a moment we will retrieve the speaker and the swing sensor.
3) CAREFULLY cut at the base of the blade
I SAID CAREFULLY! This is where the main circuit lives, but unfortunately this is also the best place to cut and separate the shell. Check the photo carefully before cutting so you don't accidentally cut the board.
I didn't know what it would look like when I opened it up, so I spent several minutes with a flashlight and a couple sets of pliers trying to figure out the best way to get in there without messing anything up. At this point, you will have noticed that the shell of the hilt is cast in two halves and glued/screwed together. Once you cut off half the hilt like in the last step, you can begin to pry it apart and see inside.
You can take your hacksaw and make a series of careful cuts along the ridge here. You really only need to cut into one half and then you can pull it apart. I chose to cut the half that has the battery case and the activator switch, which turned out to be the same side the circuit was attached to. Because of this, you might consider cutting the other side, but nothing bad happened because I was careful so maybe it doesn't matter. Gradually cut deeper and deeper along the ridge and keep testing to see if you can pry it apart. Eventually, you will be able to separate the half with the circuit screwed into it from the other.
If you are using a Dremel, at this point I would urge you to be extremely careful with how deep you make your cuts. Check my photos to see how deep the shell goes.
4) Retrieve the speaker
For this step I was convinced that I could just pry it apart, but in the end I went to the hacksaw again. You can start to pry apart the base of the hilt that we severed a few steps ago, but you may not be able to snap it apart yet. I just did the same thing I did with the last step: using the seam between the base cap and the rest of the hilt, I took my hacksaw and made a cut around the circumference of the handle. I was being cautious just in case the speaker was in a weird position, but as it turns out it is completely recessed into the end-cap, so you can really cut as deeply as needed here. At some point, you'll still need to pry the two halves apart, but after making your cuts this will be quite easy. Once separated, take the speaker, the swing sensor (the little canister that feels like it has a ball-bearing inside) and the end-cap and set them aside.
5) Free the circuit
Easy enough. Remove the screws and claim your prize. If you cut the four wires already that lead to the speaker and sensor, you can easily pull the rest of the wires through the molded holder on the battery pack. Cut whatever you need to at this point - we'll be soldering extensions onto the wires anyway.
I've seen someone actually desolder all the original wiring and sensors on the board because of how flimsy they are. If you want to do this, great; but unless you're planning on using it for combat, I don't think this is necessary.
6) The battery pack
This part may be optional if you have a better way to get a battery pack into your hilt. I thought I would be able to find a better way until I tried this.
Take your Dremel and carve the battery holder away from the shell. Try to cut a bigger piece than what will fit your custom hilt. Then trim away the shell until the battery pack fits snuggly (but not too much) into your hilt. You want to be able to pull it out without much fuss, but it still needs to sit firmly.
7) Circuit channels
As long as we've got the tools out, let's do one quick modification to your new custom hilt. In order to make the circuit fit at the tip, we'll need to make a couple of channels in the inside so it can slide in and out. I took a small file and made straight channels on opposite sides of the inner pipe. How far they need to go depends on how deep you want the LEDs. I wanted mine to be far enough back so that some light would bleed through the sides of the emitter. It will take some time, but eventually you will be able to slide the circuit into place and thread the wires through the bottom.
Okay, so at this point you should have a smoldering pile of a former lightsaber and lots of electronic goodies at your disposal. Make sure you've got:
-The main circuit with LED board attached
-The swing sensor
-The end-cap (where the speaker was housed)
-(possibly) The battery holder
Step 2: We Can Rebuild It - We Have the Technology
If you've got your lights, sound, and swing sensor working, we can go ahead and start planning how long the wiring needs to be in order to not only fit everything in it's new place, but also to take the thing apart and replace batteries. As you can see in one of the pictures above, I spared no expense when it came to the length of my wiring. My plan was to keep the circuit and LEDs as far to the front of the emitter as possible, run the switch wires through the conveniently placed hole, sit the battery pack halfway down the lower pipe, and have the sensor and speaker in the lower half of that pipe. Because I also wanted to be able to pull the hilt apart for maintenance, I avoided using too-short lengths of wire.
To make all of this work, I had to cut the section of the pop-up drain pipe that goes into the wider one so there would be space for the batteries. When you do this, make sure you leave enough room so that the smaller pipe still has enough length to sit firmly in the larger pipe. If you leave about 2 inches below the nut, you should be good.
The Switch Contacts
The first thing we need to tackle before anything else is the switch. Apparently the Darth Vader board comes with wires already soldered to the board, but the Anakin uses a contact button, which means we'll have to make a wire contact ourselves. In the closeup photo of the board, you can see what I did to make this work. Fortunately, for one of the switch wires you can use the connection next to C6 that's already soldered. (I promise I went back and cleaned up that poorly done connection before everything was done).
For the other wire, we have to make our own contact in the area above where you just attached the wire. If you try to get a glob of solder on there right now, it'll just pop right back off again. In order to make it stick, you will have to scratch the coating off the trace until you can see the shiny part of the board underneath it. I used the tip of a pocket knife. Do be careful because you could either scratch through the board or make a connection where there should be no connection. Once you've got an area to work with, put the tip of your iron to the new contact and melt a glob of tin there. Then take the end your wire and attach it to the board. Make sure both connections are really solid (unlike the sloppy one in my picture). Hopefully the pictures give you a clear idea of where everything should be now.
You can attach extensions to the wires on the board while it's still outside the hilt. Once you've got each wire extended, get the circuit in place and thread the wires through the top half of the hilt. Now you can complete the wires by soldering the extensions to their respective parts. You should now have the circuit board in the hilt with all of the loose wires connected to their respective components.
Step 3: Assembling the Hilt
This next part's fairly easy. With the circuit seated firmly in place in the top half of the hilt, take the other pipe and pull the speaker and sensor through. Next slide the batter pack down until it's sitting about half-way down the hilt. Now take some very thin pliers or tweezers and pull your switch wires through the small hole on the upper half (the white wires in my photos). You'll still have some excess wiring, but you should be able to easily curl it up a little and get it into the hilt. And that's it. Now you can reassemble the whole hilt and touch the switch wires together to activate your saber. Just make sure your hand is clear of the blade!
Step 4: The Switch, Finishing Touches
You can use whatever switch you like, but the one I listed on the first page from Radioshack really did the job for me (http://www.radioshack.com/product/index.jsp?productId=2062508.) Whatever switch you choose, make sure it's a momentary switch and not a toggle.
Solder one of the wires to each lead on the switch and then test it to make sure it works.
I was having a hard time figuring out how to get the switch to stay in place without using glue (in case I need to replace it easily.) I ended up at an electronics store and they had these thumscrews for computer cases so I picked up a couple of bags and it turned out to be exactly what I needed. I drilled a small hole in the side of the switch section of the hilt (test the size on something else first so you don't make it too big) and it just so happened to hold the switch in place while making a nice visual addition to the hilt.
Congratulations! You just made yourself an awesome lightsaber! If you want, you could think about fitting a blade onto it, attaching a belt clip, or making more modifications. Hope you enjoyed following my instructable! Post pictures in the comments so I can see your handiwork. And may the force be with you.