Hi,
A am looking to make a large LED display for our local community swimming pool - numbers may be 150 to 300mm tall with the units at the end ..... so something like 28.4~C (~ = degree symbol). Could be segment or matrix.
I guess this has been done before but any tips on how to achieve this in a simple, cost effective manner would be great 
Cheers
Sparkfun do a 6.5" high 7 segment display at:
You could always make your own if you want one bigger, you can use normal led's with acrylic or similar over the top making the shape of the display and acting as a diffuser. Easier to build than making a large LED matrix!
Hi Programmer - that's perfect - many thanks... wonder if these are available in the UK?.... nothing showing on the Google.
But they are not cheap.
Hi Mike,
Thanks, even bigger But like you say not inexpensive - maybe I will ask if they will help out with a charity project
Cheers.
Sparkfun aren't too expensive for postage to the uk...
If you look at this: 12ft GPS Wall Clock - SparkFun Electronics then it should give you some ideas of how you can do it bigger... 
Regards,
Mowcius
Hehe, now that would be fun
You could use my LED driver board to drive it. This link is a description of rev 2 of the board: effluvia of a scattered mind: Lightuino Design Thoughts. I haven't made a formal purchasing site yet, etc. But the code is here: Google Code Archive - Long-term storage for Google Code Project Hosting.
It is based on 2 M5451 chips which will do 35 outputs at 12 volts, 20mA. Since it is not a matrix driver the LEDs are on solid. This means that they are a lot brighter (an 8x8 matrix only has an individual row on 1/8 of the time). And you can have multiple lines drive the same LED if you choose to use high brightness LEDs instead of multiple low brightness ones.
Speaking of brightness... are you expecting that the display will be visible in full sun (you said it was a swimming pool)? If so, you might want to experiment with that to make sure it actually works before jumping into the project. Note that the sparkfun video has the lights off, AND they are using green (the eye is much more sensitive to green) -- so I'm guessing its not really that bright. Really its more likely that a mechanical solution (I'm thinking of a rotating styrofoam drum with numbers painted on it, slot machine style) will be visible in full sun. You could use the arduino to drive continuous rotation servos to move the drums. Of course, the mechanical solution doesn't look as cool!
dear, maybe you can get some new idea from some led display manufactuer.
contact http://www.megalightled.com/index_en.asp , which maybe benifical for you.
I'm using the sparkfun 6.5" leds on my project along with KTA-255 driver board. I have not gotten the KTA-255 to work yet. I have to get or make a RS232 or USB to TTL converter to run their setup software. 
vxir asked:
are you expecting that the display will be visible in full sun (you said it was a swimming pool)? If so, you might want to experiment with that to make sure it actually works before jumping into the project.
Yeah, the issues really are size and brightness. Visibility-wise, bright LED segments would probably work fine on a black backing panel.
Since I [heart] 7-segment displays:
Windell at Evil Mad Scientist Labs couldn't resist buying and wiring up a giant (12"!) digit he found in a Chinese electronics mall:
http://www.evilmadscientist.com/article.php/sevensegment
$55 each at their store may be too pricey for your project, but at >2W per segment, they're pretty bright.
Eagle Displays sells a bunch of big displays, but I imagine they're pricey since they want your contact info before even showing you the specs:
http://www.eaglecontrols.co.uk/numeric-time-temperature.php
Futurlec has two 7-segment digits using multiple LEDs, but the big one is pretty pricey too:
and here's a homemade 6" 7-segment digit:
It would be awesome to do it with something more unconventional, like small incandescent bulbs or fluorescent tubes. realities:united built a very cool 2-digit 7-segment display hanging from a ceiling:
But the best would be... neon! 21 identical tubes for the 3 7-segment displays, plus a decimal, degree symbol, and a "C"; should be visible under any condition... I have no idea how you'd control the switching (maybe easy using automotive neon), and it would be far from cheap, but that's a display I'd love to see!
Not sure what the point is; it always seems like its too damn cold when you get into the pool, and too damn cold when you get out!
But the best would be... neon! 21 identical tubes for the 3 7-segment displays, plus a decimal, degree symbol, and a "C"; should be visible under any condition... I have no idea how you'd control the switching (maybe easy using automotive neon), and it would be far from cheap, but that's a display I'd love to see!
This was waaaay better (and brighter, and bigger...):
http://beautifullight.org/beautiful-light/gallery
CCL tubes might work also!