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### Topic: 1,280 four state LEDs? (Read 940 times)previous topic - next topic

#### cowjam

##### Jul 06, 2010, 02:27 pm
Afternoon,
What would be the best / easiest way to control an array of 1,280 (or a large number. More than a few anyway) LEDs so I can tell each LED to be off, on, 33% or 66%?

Would it be PMW control or having three circuits, each with a different voltage, or is there a way to vary resistance? I don't really know, that's why I'm asking.

I have an Idea, but I don't know how to go about it.

#### Grumpy_Mike

#1
##### Jul 06, 2010, 03:03 pm
Anything involving that number of LEDs is not going to be easy or cheap. Especially as you want to control them individually and proportionately.
You say an array but do you want a matrix and refresh / multiplex it or do you want control over each LED.

Probably the best bet is by changing the voltage applied to the LED by use of a 2 bit D/A made from resistors. It is not clear if you want 33% power or 33% brightness but this is not the same thing. If it is control of brightness you want then you will need maybe more than 2 bits per LED.

If you look at your cost per LED I can't see it being less than \$0.50 which makes it an expensive project.

#### cowjam

#2
##### Jul 06, 2010, 04:03 pmLast Edit: Jul 06, 2010, 04:05 pm by cowjam Reason: 1
To explain myself, I have one of those sparkfun UART cameras.

It's minimum picture quality is 2 bit greyscale (so four states). I'd like to grab a picutre and have it displayed on LEDs.
1,280 LEDs is 40x32 which is half the lowest pixel depth that camera will do.  I could go lower, especially as proof-of-concept.

So, by voltage I do mean brightness.

edit: I've realise I could use 8x8 LED matricese, 5x4 would be the same resolution as my 1,280 LEDs.  Would that be easier?

#### Grumpy_Mike

#3
##### Jul 06, 2010, 07:51 pm
Quote
Would that be easier?

Yes but I doubt it would work. This is because I think you would have to multiplex them and there would not be enough time to do the multiplexing and read in the image. It is also more difficult to control the individual brightness of each LED when you are refreshing a matrix.

#### cowjam

#4
##### Jul 07, 2010, 10:26 am
Thanks Mike.

I might try reduce it to on/off, and a much smaller display (I've got four 8x32 LED matrx displays so I can try a monochrome 32x32 display).

#### Grumpy_Mike

#5
##### Jul 07, 2010, 11:54 am
Are you trying to make something like this:-

#### cowjam

#6
##### Jul 07, 2010, 04:40 pmLast Edit: Jul 07, 2010, 05:09 pm by cowjam Reason: 1
Yeah, that's pretty much what I want to do.

I hope to get better contrast so it'll show a face.

edit: but not live. I'm quite happy to do snapshot, process, display, wait for trigger and repeat.

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