As you may know, Evelyn has been working on a Bat display sign. This is a “eye catcher” we’ll use to help draw people to our booth. After a lot of work, she came up with a good way to matrix the LEDs, and it’s very close to completion.

After many discussions, we decided to make the control unit modular. That way we could use it for other signs. To do this, everything is plugged together to a control box (versus being hardwired). It took more time to do this, but it means a more flexible design, and it’s more “bullet proof”.

In the end, we decided to go with standard D-SUB 9 pin connectors. They are pretty easy to work with and very common. (They are those old “serial port” connectors you see a the back of older computers; pre-USB.) Anyhow, we needed a project box and found one at are local second-hand shop. And old VGA switchbox, made of metal. The beauty of it is that it had most all the right hole already drilled.

Here’s a front view of the control box:

The jack on the left is a 1/4″ “audio” jack. We decided to use this for power, since it’s jumbo-sized, and we had the parts on-hand. We replaced the old rotary switch (and guts) with a toggle switch. It toggles between “on”, “off”, and “program” modes. There is a small status LED to the left of the toggle to let us know that the box is working. The whole unit is sitting on its lid.

The only hole I needed to drill was for the 1/4″ jack. Since it’s thick sheet metal, that process was a bit of a pain in the butt. Luckly, we had recently purchased some new drill bits (and got our big drill out of storage). I cleaned up any burrs with a Dremel and a diamond bit.

Here is a rear view:

Isn’t it nice when an old piece of equipment works perfectly for a new project? The original box had three DB-15 high-density connectors, which are the same size as the DB-9 we’re using. No cutting, thank goodness! Plus, they supplied the hardware to mount the connectors.

Finally, here is a top view into the unit:

At the bottom, you see the three DB-9 connectors. There are three sets because we have the unit wired in a 3 x 8 matrix. Three columns (wing, body, wing) and 8 rows (sets of LEDs in the sign).

At the far left is the battery for the Arduino. We kept it’s supply separate, in case we need to drive LEDs off different supply voltages.

Next you have the stripboard, which has a Boarduino on it. That’s a version of the Arduino from AdaFruit. It’s small and easy to work with. Evelyn has it plugged into some female headers, which are then soldered to the board. This allows her to pull the board out, if necessary. The Boarduino has a programmer connection on board (between the blue and yellow DB-9 connections), so it can be programmed without being removed.

To the right, the rest of the board has the PNP (columns) and NPN (rows) transistors. After mucking around, and having much trouble with, smaller transistors, I suggested we go crazy and drop in some TIP107 and TIP102 transistors. They are really super-overkill, as they can handle 100V and 8A, but what the hell. They worked perfectly, and we don’t have to worry about overloading them.

Finaly, in the upper-top-right you see the back-end of the toggle switch, status LED (with lots of hot-glue), and the 1/4″ power jack.

What you don’t see is a little cheat-sheet I wrote up, which I wish more people would do: It’s a document, pasted to the inside of the cover, which lists the color codes, pinouts, and so on. It will allow us, in a years time, to crack it open and not have to guess as to “what does what”. Kinda like the old schematics that TVs and Radios used to have — when you could service them on your own.

And here’s the final bat sign, with the whole “cave” cutouts.

In addition to the pink LEDs backlighting the bat, we have three super-bright white LEDs located behind parts of the cave. (They aren’t on in this photo.) These give a really cool “lightning” effect and are a great eye catcher. We’ll make a movie of it and post it up. It’s quite impressive.

Update: Here it is with the “lightning” effect: