Comments on: Edge-Lit Plexiglas Demo

By: CJ

CJ — Wed, 31 Dec 2008 01:22:01 +0000

What are the implications to the world of signage with this?

By: Keith Neufeld

Keith Neufeld — Mon, 15 Dec 2008 22:13:27 +0000

Alton, I have no idea — you’d have to try it and see. I don’t even know whether plexiglas is transparent to IR.

Why would you want to use the plexi? Why not just have the IR LEDs pointing directly at the detectors?

By: AltonToth

AltonToth — Thu, 11 Dec 2008 05:25:09 +0000

Would it be possible using this method to edge light a piece of Plexi with IR LEDs, and have the edge of the plexi roughed up, an air gap of several inches, and then 4 or 5 IR detectors on the other side? I’m thinking of using a method like this as a finish line sensor for a model track. Would the IR illumination be enough? Thanks!

By: Dan

Dan — Sat, 22 Nov 2008 16:46:56 +0000

We used to use clear perspex sheets mounted in a wooden box with a strip light inside it over maps in the command bunker when I was in the Army in the 80′s/90′s. When the map was annotated with Chinagraph pens, the notes used to light up.

No photos though, for the obvious reason, sorry.

By: bob murphy

bob murphy — Thu, 20 Nov 2008 04:00:15 +0000

Keith -
Just curious how bright the LEDs are that you are using (in candela or mcd)?
How about the SMT LEDs, also?

I tried a quick experiment of my own on broken shards of CD jewel case and even discounting the camera bloom, the lighting effect was not very noticeable. I was trying to figure out what was different with my experiment. I think the LEDs in my quick test were 630 mcd.

By: Dave

Dave — Tue, 18 Nov 2008 15:24:16 +0000

There are a couple of approaches to driving such a light system. If you really need programmability, the usual approach is to use some type of microcontroller. Microchip makes the PIC series, and Atmel makes the AVR series, both of which are fine microcontrollers. Of course, you are responsible for building a board to install the microcontroller on and for programming it. A variation on this approach would be to use something like an Arduino:

http://www.makershed.com/SearchResults.asp?Cat=43

(which, if I’m not mistaken, is based on a AVR microcontroller).

One of the tricks to minimize cost is to use a smaller microcontroller (e.g., one of the 8 pin ones), and use a shift register to actually drive the LEDs.

You could, of course, use a PC to drive the system, probably building some type of latch based system that’s operated via a parallel port (e.g., a handful of 74LS374s), but that would, almost certainly, be overkill.

If you don’t require programmability, but only want to “randomly” sequence the LEDs, then you may be interested in a LFSR (Linear Feedback Shift Register) PRNG (Pseudo Random Number Generator):

http://en.wikipedia.org/wiki/LFSR

You can build one of these with a clock generator (e.g., NE555 chip), a TTL shift register (or two, or three, or ….), and an 7486 XOR gate.

Dave

By: Keith Neufeld

Keith Neufeld — Tue, 18 Nov 2008 13:12:42 +0000

Damien, as I noted in passing, this demo has no microcontroller, just male headers sticking out of the breadboard that you run a wire along to light the LEDs. However, I just bought a batch of Allegro A6276 16-bit LED drivers, and I’ll be controlling them with an Arduino in the final piece.

The A6276 is rated for 90mA per segment, if I’m remembering correctly, and I think you can use a higher drive voltage and run multiple LEDs in series. I might look at doing four parallel strings of two series LEDs at 20mA per string, 80mA total.

You can daisy-chain the A6276, so two chips would get you your 25 segments plus a few spares you could use for indicator lights or whatever else.

I hope you’ll come back and post a pointer to your work when you get this thing going!

By: Damien

Damien — Mon, 17 Nov 2008 20:54:36 +0000

Hi, firstly thank you. Cool blog entry and a nice effect. Secondly, I was hoping you might be able to give me some details of the microcontroller set up you used.
I’m trying to create an LED display with 25 independently programmable sections, with up to 8 LEDs in each (all 8 being on or off together).
I know what I want to do, and I’m not afraid of getting dirty with the wiring, but the programmable bit I’m lost on.
Any advice anyone could provide on a simple (/simplest) way to achieve this would be greatfully appreciated.
Thanks

By: Adam Ray

Adam Ray — Wed, 12 Nov 2008 19:01:35 +0000

Really nice

By: Keith Neufeld

Keith Neufeld — Fri, 07 Nov 2008 16:32:22 +0000

Dave, the edges are all rough-cut from a bandsaw, no sanding except on a couple of them. Interestingly, some of the most even visual effects (not discernible in the photos) are when the bottom edge is rough and the top edge is smooth.