My kid wanted a robot costume. I didn't take pictures as I was doing it, but it's easy enough to understand with the completed project pictures.

Supplies

Some scrap corrugated cardboard. The torso front should be one flat piece.

1 cell battery (3V). Most common is the CR2032, used in LED throwies.

1 or more 5mm LED.

Copper tape. I used about 1 meter of for this large 4 LED circuit.

All the hot glue. I mean, that's the quantity I used, but I guess it varies.

Step 1: Design Your Circuit (or Just Copy This One)

The first picture shows the whole thing. That copper tape X in the middle is the common negative that connects to all LED cathodes (the shorter legs). Just think of it as the minus (-) of the battery.

The second picture shows exactly how the battery is hooked up. The shiny flat size with the plus (+) on it is the positive. The other size, the weird one with no writing on it is the negative (-).

I got the third picture off the webs because I didn't take pictures during the process, sorry. Basically, you want to place the sticky side facing up to stick to the negative part of the battery, then fold the tape once in a 90 degrees angle so the sticky side faces down towards the corrugated cardboard and you run it from there. Just be careful so that the copper tape doesn't connect the positive and negative sides of the battery.

The positive side is way simpler, just run the tape across the battery, sticky side always facing down, to attach the battery to the costume. Check the pictures, they are pretty self-explanatory. Again, don't connect the (+) and (-) together. That way leads to dead batteries and worst.

That last picture is where the magic really happens. The positive strip running down in 90 degree turns never actually touches the other strips that run along side it. You can probably guess why it's that way, but the next step will make it all clear.

Step 2: Magic!

So, on that right side of the picture you have:

(a) one strip that is connected to the positive (+) side of the battery

(b) Four other strips that are connected to the anode (longer leg) of each LED

To light any LED you just need to connect (a) to (b), making the (+) from the battery reach the intended LED.

I hot-glued some black cardboard to the base and carefully placed a small copper strip to make a simple switch. You just need to lightly press that switch and a LED lights up. See picture.

Step 3: Just Use Your Imagination... and One Million Hot Glue Sticks

I made the circuit on the box that I knew fitted my kid, but you can make it anywhere and glue the whole thing on the costume later.

Do make a support for the top of the head, so the mask doesn't fall on to the rest of the costume, because that limits movement. I cut and glued and tore some of the costume apart for adjustments, but hot glue always came to the rescue.

I used a bit of old nylon stockings for the eye cover, some toilet paper tubes for the robot ears and my wife and kid decorated the whole thing. Yes, those other colored circles just look cool and that's their only job. And I think they're great at their job.

Hope you liked it, maybe you got an idea or two from this. So that's my first instructable. Is this where I say "comments below"?

Have fun, everyone!