Huge Seven Segment Display #3

Enclosure Design

This is my third post on the days-accident-free counter I made for Nottingham Hackspace. See the first one here and the second one here

This post is on the design of the counter enclosure and the digits and individual LED segments.

I wanted the enclosure to have a “hacked together” look-and-feel, to fit the theme of the piece (accidents), and also because my woodworking skills aren’t that impressive. If it’s going to look crap, it may as well be intentional.

The basic way to get LED segments of this size seems to be using LED arrays behind some sort of diffusing material. After searching the hackspace for a bit, I found some sheets of fibreglass-like material that looked pretty much ideal, apart from being marked with a manufacturer’s stencil. I decided that this wouldn’t be noticed once mounted on a wall, and luckily I was right. The size of the sheets pretty much dictated the size of each digit.

Rather than cut out the segment shapes from foamboard or anything like that, I went down a much lazier route of laser-cutting the mask out of black card, which was glued behind the fibreglass:

Masked out digits

Two masked digits

Making the masks this way was really, really quick and created zero mess. (read Sparkfun’s adventures with styrofoam to compare). But with just those masks, the light from one segment would diffuse into another without a separator. These just ended up being bits of pine strip cut to length and stuck down in the box. And the box itself is pretty simple, just an MDF base and plywood sides:

Box Components

The basic components of the box: diffuser, mask and separators.

Each segment uses three 5mm “Piranha” LEDs. If you’re interested, I’d recommend Phenoptix for all your LED needs. Especially if you live down the road from them and go to the same hackspace.

The LEDs are mounted on stripboard and have 240R of current limiting resistor per segment. Cutting up the stripboard and attaching mounting standoffs, and then the associated soldering was; if not most time-consuming; at least the most boring part of the project. I just hot-glue-gunned each LED strip into place in the box.

LED boards

LED boards glued into case and wired up

After all that, the result is a box full of LEDs and strips of pine, and some bits of fibreglass with card stuck to it. To attach the segments to the box and allow access for maintenance, I use a long hinge that (luckily) happened to be in a box of fixings. Together with some strips of aluminium and an old metal box I cut up, I managed to get a suitably horrible looking front for the box:

Single digit with metalwork

Bits of metal to finish off the “hacked together” look

The one lesson to take away from all this is that the “black card and bits of wood” method is really good for a quick-and-dirty way to make massive LED segments. Replacing the wood with plastic or anything else suitable would work just as well.

More to come soon/later/in the far future. The next post will look at the electronics in the auto-dimming LED drive – designed to dim the LED segments when the ambient light level drops.

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4 Responses to Huge Seven Segment Display #3

  1. Pingback: Huge Seven Segment Display | Return Zero

  2. Pingback: Huge Seven Segment Display #4 | Return Zero

  3. James says:

    Hi,

    I am looking to do something similar to this for a school project and I am having trouble getting a good diffuser (aka something that I like) for the LEDs. I have tried just sanding some acrylic but I am not too fond of the outcome. Would you mind giving me some more details on the material used such as where it can be purchased or some specifications of the material? I do have access to a laser as well but I am not sure of whether or not it would even be able to cut through such a material, but I would like to try because this looks to diffuse way better than mine does at the moment.

    Thanks!
    James

    • fowkc says:

      Hi James,

      I’m not sure what the material is, it was in a pile at the Hackspace. I can try to find out next time I’m there.

      I think the photos of my counter make it looks better than it is. You can still see the individual LEDs when you look at it in real life.

      I think the easiest way to solve that is to use more LEDs in the same space, if you can afford to. Thicker diffuser material, or more layers of it, might help as well.

      I’ve read that a few sheets of thick tracing paper can work well as a cheap diffuser, but I’ve never tried it.

      Hope that helps a bit,

      James

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