>so hopefully if I get some STX790ATransistors, It will be ok - is this just a simple swap job?

I'm not sure what your present limit is. With 100 ohm resistors, your transistors are probably being overdriven-- which only means that they might explode; it does *not* mean that they are underperforming before they explode.

But... yes, replacing them with devices that can handle the current there is a good idea. They are plug-in replacement parts. However it *may* not improve the actual brightness-- that depends if you are voltage limited or not. The '790s will get you an extra half volt or so, which could make a big difference.

One more turbocharging option to consider: After (and *only* after) you install the '790 transistors, you may also want to replace the "base" resistors that drive those. Maybe take them as low as 200-300 ohms. This will give you 2-3 times as much control current into the transistors, which can potentially allow 2-3 times as much current to pass through the transistors.

You may also consider adding a big 10,000 uF +, 10 V+ electrolytic capacitor to the board, near the LED driver chips, and watch the polarity.

Additional suggestion: solder the LED driver chips directly to the PCB, without sockets-- that will reduce the odds of them overheating.

>Hopefully this will improve it enough.

Can't say. Here be dragons.

Dave,

How did you handle the wires to the LEDs on the board itself? I was contemplating using copper tape, with electrical tape to cover where it would cross. Or using stranded wire and an SMD rework tool to selectively melt off the insulation every 3 inches.

How did you handle the wires to the LEDs on the board itself?

I created a 60mm grid using 7/0.2 equipment wire, melted the insulation off for the Led connections. This is wired to two 25 pin d-subs, I then have two lengths of 25 core cable connected to the peggy via more d-subs. I broke out the peggy board by simply putting a row and column of pins on the pcb, these are wired up to some d-subs on the project box.

If I were to do this again I think I would use a bare wire and selectively insulate parts of the grid, to avoid the mess, fumes, and bad sticky connections.

Are there any other easily available suitable transistors other than the STX790A's? As they seem to be unavailable or not in stock in the usual places.

Maybe I just stick with the display how it is now, It looks really cool in its ambient dim kinda way, but I also know it would look wicked if really lit up. Maybe I will have to leave it for now, since its getting close to the first exhibition, and It is working, but for the following one I will def get it brighter.

Seem to be in stock at digi-key, 497-4430-1-ND.

Quote by: Windell
You may also consider adding a big 10,000 uF +, 10 V+ electrolytic capacitor to the board, near the LED driver chips, and watch the polarity.

[/p]

Do you mean in parallel, between 5v and ground, to control power fluctuations?

>Do you mean in parallel, between 5v and ground, to control power fluctuations?

Yes, that's the idea.

Finally got around to uploading some pictures. Generally speaking the project was a success, it looked good and people enjoyed it.

However one of the main features of the installation was that it was meant to be suspended in the air using a giant helium balloon... unfortunately it was very windy that weekend and my fear was too great. Designing it to be very lightweight also meant it was pretty fragile and so come Sunday night it was very broken.

anyway pictures are at:
picasaweb dot google dot com/originalav/

project page:
http//:www dot umoon dot net

next year will be bigger and better! no quick hacking this time - gotta be rgb & wireless

thanks for your help everyone.


(strange - urls would flag it as spam)

Wow-- this is really an amazing project. We might feature this on the blog, if you don't have any objections.

cheers. sure feel free!

Hey Dave,

We should totally link our large Peggy displays via the internets in some way!
http://www.flickr.com/photos/mrbon/sets/72157622151360228/
Maybe they could play Pong against each other? Or use Jay Clegg's video Peggy code to do split-screen video chatting at ridiculously low resolution? Any other ideas? Where are you located?

That would be awesome! unfortunately my display was in a bit of a sorry state and decided to leave it in the uk for the time being (i've just moved to vienna). Will let you know if I bring it back to life any time soon though. Loving your work by the way - looks great!