With a craft knife, cut off the top of the cardboard letter. It’s easiest to make a rough cut first, and then follow up with a second cut to get closer to the edges. Once you’ve finished cutting, you can smooth the edges of the letter with sandpaper, if you want.

Using a ruler, on the back of your letter, measure where you want the LEDs to go. They should be about 1.5″ apart. With a pencil, mark a small X at each spot.

Using the craft knife, carefully cut a small crossed slit at each X. Then, gently poke the pencil through each slit, going from inside the letter to the back, to make a rounded hole for each LED.

When the holes are made, it’s time to decorate! The hollow inside is what people will notice. First paint it with acrylic spray paint, using the paintbrush to touch up the cardboard edges or add decorative details. Then add stickers or cut-out images for decoupage, sprinkle it with glitter–whatever you want. We painted ours silver to give it an old-timey look, then we painted the outside black. When you’re done, let everything dry before continuing.

Use a black marker to darken the long positive (+) legs of each LED, so you can easily see them. Then use the wire strippers to clip each darkened leg so it’s only about 1/2″ long.

Then use the wire strippers to clip one leg of each resistor (it doesn’t matter which one), so that each is about 1/2″ long. Set the resistors aside.

From the front, gently wiggle one LED into each hole. Then, on the back, bend down each LED’s short negative (-) leg and orient them so they’re facing in the same direction. Using the hot glue gun, glue each LED in place. Glue from the letter’s (hollow) front, while pressing the X cuts in place on the back; this is to hold the LEDs tight and to keep the glue from running down onto the LED legs.

When you’re done, each LED bulb should be sitting flat inside the front hollow of the letter, and each negative (-) LED leg should be pressed flat and aligned on the back.

When the glue is dry, flip over the letter. On the back, twist the clipped end of each resistor to the clipped positive (+) leg of each LED.

Using the soldering iron, solder each connection. Bend the wires down flat and, using wire strippers, cut off any wire that sticks out beyond the outer edge of the letter.

We’re using resistors here because we’re wiring in parallel, using more battery power than any one LED can handle. The resistors will “resist” the extra voltage so the LEDs don’t burn out.

Using wire strippers, cut a piece of red hookup wire that is long enough to connect all the LEDs, plus a few additional inches. An exact measurement isn’t necessary; you just need some extra wire at the end to attach the battery holder. Strip both ends to expose about 1″ of wire.

Hold the red wire along the LEDs and, with the black marker, mark each place the wire meets an LED. At each of these points, you want to strip enough covering away to expose a small bit of wire, which will be solder points. A quick way to strip the insulation in these places is to gently roll the wire under the blade of the craft knife, then slice lightly along the length of the wire and pull off the insulation. When finished, the red wire should look something like this:

Repeat steps 8 and 9 with the black wire, so that it measures and looks the same as the red wire, except that the black wire will connect to the negative (-) legs of your LEDs.

When both wires are ready, use the soldering iron to solder the red wire to the free ends of each resistor. Then solder the black wire to the negative (-) LED legs.

Using wire strippers, clip off any extra red or black wire at the end of your letter. If the leads on the battery holder aren’t already stripped (some come that way), use the wire strippers to strip the ends of the red and black leads on the battery holder. Then use the soldering iron to solder the battery holder leads to the letter’s two wires: match red to red and black to black.

When everything’s working, use the hot-glue gun to touch a drop of hot glue over each solder connection to protect them.

To finish up, cover the wires in back with electrical tape and glue the battery holder onto the back of the letter (make sure you can still open it!).

The letter you’ve created can now stand on its own, but you can also hang it up, We used double-sided foam tape, but be sure you get an adult’s permission before you stick your letter to the wall! It will also look great just sitting on your bookshelf.