Introduction: LED Birthday Cake Billboard

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For my wife's birthday, I wanted to do something special that tied in with the present I was giving her - a felted version of a succulent plant arrangement. I followed - in spirit - an instructable here on making succelent-themed cakes, but with (umm) limited success. So, I decided to spice the cake up a bit with an LED "billboard" that would give the cake the air of being truly freeway-desert-esque...

I had a bunch of 10mm LEDs available (from our Instructables LED build night - thanks!) plus some lithium coin cells, so I figured I'd custom-build a "billboard"-style sign using these parts.


Materials required:

-10 mm LEDs

-4x coin cell CR2032 batteries

-20 gauge wire (for battery leads)

-30 gauge wire (for wire-wrapping the LED leads)

- wire wrapping tool (yay old skool styles!)

-hot melt glue gun (tool of hacker champions)

-bamboo skewers (for the frame, another tool of hacker champs)

Keep in mind I had a limited time-frame for this build - it was only after the cake turned out to be below expectations did I need to add some pizzaaz to the presentation. In retrospect, I could've saved time by soldering the LED leads to a bus wire, and the hot glue work was a bit of a hack, but it served the purpose and turned out well... :-)

Step 1: Assemble LEDs

The first step is to create some LED strings that will serve as the basis for the sign. I chose to use a 6x4 LED grid, since it seemed to give the best resolution for the 10mm LEDs while still making a clear sign.

I built these up in steps, hot-melt-gluing one LED to another to form LED chains.

Step 2: Build Numbers

From the LED strings, I built up some crude number shapes. In this case, a "4" and a "1" (sorry dear, but now everyone knows your age... :-)

Hot melt glue was essential to this step. However, note that hot melt glue is, umm, hot - so prepare yourself for some scorched fingers. :-)

Step 3: Frame Numbers Together

Next, I assembled the numbers together with copious amounts of hot melt glue and some handy bamboo skewers. I wanted a cross brace to connect the numbers, but two upright posts to anchor into the cake. Once the glue had cooled/set, I used a pair of snips to trim the extra skewer material away.

Note - the uprights used the pointy end of the skewers to aid in anchoring in the cake. I left a generous amount of skewer, since I had a double layer cake (the bottom layer was supposed to have gummy worms dispersed throughout, but the heat of the oven prevented that from working out successfully).

Step 4: Wire LEDs

I decided to go old-school and use my wire-wrapping tool with some 30-gauge wire to connect all the LEDs (preserving polarity, of course). In retrospect, I should have soldered the leads instead, since the wire wrapping got tired pretty quickly. Wire management also got a little bt hairy, but nothing that copious amounts of holt melt glue couldn't bring under control...

Step 5: Build a Battery Pack

I wasn't sure how much current the LEDs would require, so I played it safe and built a battery pack with 2 CR2032 cells in series, that was duplicated in parallel. I hacked together a battery holder with some old binder clips, some hot melt glue, and some 20 gauge wire. It seemed to work well so I declared it "done" and moved on.

Step 6: Connect the LEDs to the Battery Pack... and Troubleshoot...

After connecting the various LED segments, I realized I'd been a bit sloppy in tracking polarity of the LEDs while I was wire wrapping them - which was easy (although time consuming) to correct.

Anyway, after a bit of work, all the segments were lit and functional.

Step 7: Clean Up the Wires and Attach to the Cake!

After a quick trial run on a cardboard box, things looked good and I was ready to mount them to the cake.

So, in just a few short hours, I had an awesome addition to my (less than satisfactory) succulent cake... I'd definitely say that the LED billboard saved the day!