The KGB Oracle Forums General Public Discussion (PUBLIC) The Pub USB, LED, and resistor help?

Ok, so this would be so much simpler if I had a 588-pin port on the back of my computer, lol, but I want to use USB instead.

What I'm trying to do is create a grid of LEDs, 28 wide by 21 tall, and I want to be able to write a program (which I can do no problem once I figure the wiring out) to control each LED. I want to set it up so every LED has it's own I/O, and again, I want to power the LEDs and control them through USB.

My plan is to start off with a simple equalizer to hang on my wall (the end result will be a 6x8 panel that will hang on the wall, I'll post pictures when it's done!) and eventually write a program that will allow the beast to basically double as a second, single hue, super low resolution monitor so I can write some cool visualization programs for it.

Right, so I don't even really know how to go about wiring this up, especially not once I start thinking about resistors and stuff (which I super hope I don't need).

You'll need them.

I'm not up on the specs that USB power provides, but a typical LED needs ~3vdc to light. You're talking nearly 600
LED's here.

At the bare minimum, you'll need resistors in place to drop
the voltage down to something the LED's can use since it's unlikely the USB port is going to natively provide a perfect
3VDC source

Amp draw should be looked at as well. While LED's don't consume a lot of it, you're talking about an insane number
of LED's. How many at a given time are going to light ?

If their draw exceeds what the USB port can provide, well
I have some bad news

Ideally I'd like to be able to have them all lit, just in case something goes goofy in my code, but I can't imagine I'd ever have more like 400 lit at a time, lol...

USB 2.0 provides 5 Volts and it starts out at 100mA (milli amps?) and can provide up to 500mA, but there are some exceptions with certain software/hardware it seems, where a device can draw up to 1 Amp. Also, with PlusPower (hell if I know anything about it yet, I just found it on Wikipedia) a device can draw the following:

* +5 volts DC at up to 6 amps per connector (up to 30 watts)
* +12 volts DC at up to 6 amps per connector (up to 72 watts)
* +24 volts DC at up to 6 amps per connector (up to 144 watts)

If that info helps you help me, cool!

http://www.eled.com/product.asp?catalog%5Fname=LEDs&product%5Fid=E1503SRD&Action+Key=New

I bought 1000 of those.

I've decided to use 450 LEDs instead and go 15x30 on a 4x8 piece of plywood, it will be MUCH easier that way.

Voltage isn't really an issue. Easy enough to wire parallel,
throw a resistor into the mix to drop the voltage to the 2.5vdc
they need. ( according to the spec sheet 5vdc max )

However, the LED's draw 20ma of current EACH. If you were to
light all 450 LED's, you're talking 9000ma or 9 amps.

It exceeds what you can power via USB alone.

The original design of 588 LED's would have had a total amp draw
of 11760ma ( 11.76 amps ) with all LED's lit.

You'll have to use an external power supply to provide the power.

To stay within the 6 amp limit with the PlusPower thing you're
talking about ( I assume it's an external power supply ) you
would be limited to 300 lit LED's at any given time.

-Daye

Power supplys run 2-300 bucks unless you know someone that can build one, or can get a discount at a supplier, or even buy used.
Back in the day when I was in school we would build stuff like this from scratch. Been along time since I used that part of my brain. But that was when apple II ruled the home computer.

Sling
Your also going to need address decode logic as well as a bunch of gate arrays and drivers to turn on and off the ones you want.
Ideally you want to get something like a rabbit micro processor development kit -- this will give you decent multiple seriel outputs and a processor to controll them.
From there you will have to build some decode logic to address your array. I would reccomend using older chip designs in dip packages instead of trying to do it with surface mount technology, they are easier to build your prototype with. You can also get breadboards and use socketed chips and 30 gage wire to wire wrap your cicuit design.