Alphanumeric LED Displays photos by Gary Fixler click images for 2048x1536 versions (~100-350kb/ea.)

Today, 100 dual alphanumeric displays from Electronic Goldmine arrived in the mail. This is a great bulk electronics place. You never know what you'll find. These were selling for $1/5-pack, so I got 20, making 100.

I originally went looking for these because in yet another moment of insanity, I decided the shelf that holds my monitors and ShuttleX Mini-PC needed a digital readout across its entire length. Since this would be in close proximity to my computer, I could easily interface a BASIC Stamp or Microchip PIC to my COM port and have a stream of important-to-me info scroll past me all day. This would include things like reminders, email notices, computer status reports, render percentages - whatever strikes my fancy.

The com port hosts 12v, I think, which means I don't need any additional power. I am a bit curious as to how many displays I can switch through before the flicker gets too unbearable. These will work on a scanning method, like a monitor or television, wherein every element is lit briefly, one at a time, in sequence, in a loop, fast enough that it looks like all the ones that should be on are on, solidly. PICs can bring me up to 40mHz, and there's a BASIC Stamp that runs at 50mHz. I have the BS2p40 already, which is only 20mHz, so I'm prototyping on that. I'll almost assuredly move everything to one of my PICs once it works.

Since I don't want to junk the whole desk up, and I realize fully that this is an eccentric hobbyist endeavor, I want to design it as narrowly as possible (in height), since the displays are already just slightly taller than the thickness of the shelf-edge they'll go across. Furthermore, it must be clip-on, or slide-on. I don't want to drill into the desk, or use any kind of adhesives. I'll probably be tired of the thing too quickly and want to take it down without leaving behind a damaged desk.

As for scanning through them, I don't know if it's the best solution, but I'm looking into using a simple 4017 decade counter/divider. I've figured out I can just use the standard 16 pins on one half of the Stamp to run ALL of the input anodes on the displays, and then block the common cathodes of each character with npn transistors, which will be turned on in sequence as the 4017 scrolls from 1 through 10, in a loop. I want to get 47 displays going (the width of my shelf), which is 104 characters, meaning I'd need 11 4017s, I think...

I might look into other options, but since I need 15 to run the anodes, I'm left with 1 pin to do the switching through characters, meaning I need to find a clock-input style method of looping through. The 4017 screams to be used for that, and chaining more than 1 gives me the ability to run indefinitely. Again, speed is a consideration. I might also look into a binary counting system. I'm up in the air about it for now. I've already set up a test Stamp circuit that lets me race through the elements of a single digit and keep only certain ones lit. I had it randomly changing all the elements at random intervals, and it looked like it was decoding an alien language. Very 80's sci-fi movie effect. Actually, I've seen a lot of current effects that aren't much better.

After laying them out in the 10x10 grid, I realized they sent me 101 displays. I contemplated letting them know, but the evil side of me said I should keep their 20-cent oversight all to myself. I hope I don't burn for this...

I was really hoping for 100 of the green displays, of which I have 2. They're grey-face as these are, though the online pic looked black-face. These are all with red LEDs. I've heard that the color red makes people feel angry, if not romantic (which might be the same thing). If I detect elevated levels of anger after this thing works, I'm unhooking it immediately, before I end up unhooking it violently!

Here's the obligatory quarter-for-scale picture.

Of course, as with everything I end up with multiples of, I had to experiment arranging them and taking photos from various angles. So, here we go!

I find it interesting how exacting all the tolerances are on the front of these things, and then they just dump quick-drying resin in the back to seal up the circuitry and reinforce the pins. Hey, it drops the price down to $1/5, so I'm not complaining - just making an observation.

I say quick-drying only as a guess. It's obviously poured resin. I've worked with making resin molds way back in high school, and whenever I let it harden too quickly, it would pull and congeal and make ripples like those in the backs of these displays.

If I squint, this kinda looks like a billboard for Spiderman 2.

I guess it has a little bit of the feel of reservoirs in a water treatment plant, too. Feel free to Photoshop in a little guy in a canoe, or a bunch of cranberry bog workers in their rubber boot-pants.

These pics are all taken with a Canon PowerShot S230 Digital Elph, mounted on a CKC Power lens adapter (looks like this), to which I've screwed in a Nikon WC-E63 Wideangle Convertor lens. It's a lot of work to get some of the functionality of my old SLRs in a digital system, but I don't mind. It's fun.

One last through-the-pins pic.

You can see a murky reflection of the camera on its tripod in this top-down view.

There's something very scientific magazine article about this picture to me. If you want to use any of these pictures as abstract technical wallpaper, please be my guest. I'll post another gallery if/when I get the display built. Now I need to find a 1"x47" circuit board!

Also in the shipment of things I ordered were 2 sets of 5 gears, which interlock extremely well. No backlash whatsoever.

I also got 6 mini joysticks. These are 8-directional switches, which sadly do not line up with solderless breadboards :( The sticks are D-style (half the cylinder removed to make a D when looked at head-on), but I can't imagine finding anything tiny enough to require that kind of precision. They almost seem like they'd work as the little button in the middle of keyboards that substitutes for a mouse. I'm more interested in using them as real joysticks to build the smallest MAME cabinet ever! Smaller than the Mini-MAME. Even smaller than the Atomic Jamie! I'm thinking about the size of these printable Paper Arcade machines.

UPDATE! (June 13, 2004) Something had seemed odd about these displays. Now I notice, thanks to a friend's comment, that they only have 13 pins. Last night I tried to get one of these to work in the BASIC Stamp circuit I had set up on my workbench. It was displaying the same elements on both characters, which were wrong. I did a test, and saw that pretty much all the pins are in a different configuration. I don't like it. The set I've been using has 18 pins, all but 1 of which are used. There's a single cathode for each character (2 total), and then 15 pins for each element. Depending on which cathode is currently connected to ground, you get the left character, the right, or both (though they'd have to be identical. This system uses more of a mirroring approach. There are 4 common cathodes, 1 each for half of each character. 2 of each match each other for left and right, and the opposite pairing matches in mirror fashion across the center of each character. It will make more sense with the Flash demo I whipped up. Click on one more of the black pins to turn on a common cathode. Then click combinations of red pins to see the effect. In real life, at any given moment, only one cathode (black), and one anode (red) will ever be active.

UPDATE! (June 28, 2004) I got in a shipment of 16 8x8 red/green matrix LEDs. I took some artsy photos with them, too. See the new gallery.