What should I do if I want to output through HDMI?

[fungus]

On Friday, June 15, 2012 8:55:54 PM UTC+2, Daniel Pitts wrote:

Anybody remember the "Demo scene" in the late 80's early 90's? Those are
the kinds of things I'm thinking of. Simple "fire" and "plasma" effects.

Been there, done that.

If my main aim was to do that then
I'd use a Raspberry Pi. You even get
hardware OpenGL.

A big LED cube driven by an Arduino...

I've got one of these planned as soon
as I get some free time. I already
bought some parts, including an SD
card shield to store the light sequence
files.
Storing light sequences?

....or scripts, effect files or whatever
you can dream up.

I'm going to start with 4x4x4
and aim for 8x8x8 when I figure out
how LEDs interact with the human eye
(they have to be multiplexed).
The LEDs don't interact with the human eye, they only act upon it.
Unless you smash your face into the LED cube, but I wouldn't recommend
that

I'm more worried about how dim they'll
get under heavy multiplexing. Maybe I
can up the current a bit to compensate,
most LEDs can lake 100mA with a low PWM
duty cycle.

Another option is be to latch them all
using banks of serial to parallel
chips but that's a lot more hardware.

If you refresh the entire display somewhere
between 24hz and 60hz, you would get a decent
persistence-of-vision.

I was more worried about brightness,
even with a 4x4x4 cube the LEDs will
only be on for 12.5% of the time
(assuming eight output lines).

... reduce the effect of reference-frame
shifts (people moving or the device moving),

Good point, I hadn't thought of that...

So, if you multiplexed in a way that turned on exactly one LED at a
time, you'd have to update 8x8x8 (512) per frame. If you had only
on/off, and wanted a 60hz refresh rate, you'd need to update points at
30.72kilohertz. If you wanted 4 levels of intensity, you'd need 122.88khz.

Of course, if you controlled 8 leds in parallel, you could reduce that
rate by a factor of 8. which would be 15.36khz. That means you have 65
microseconds to choose values for that particular 8 led pairs.

A lot of the projects use a serial-to-
parallel chip for the data outputs
so you only use three Arduino pins
for that. The rest of the pins are
used to select blocks of 8 LEDs in
the matrix.

If I'm doing my math right, that gives you 260 instructions on a 4mhz
processor to set the values how you want. If you only have a 4x4x4 cube,
you have an 2083 instructions.

Does all this seem correct?

Depends on the controller...

Arduinos usually run at 16MHz.

On a related note of obtaining LEDs... You might already know this, but
you can get batches of 1000 LEDs on ebay pretty cheap.

Yep. Parts are hard to get where I live
so I buy lots of stuff on eBay.

Get hold of a 14 segment display...?
I suppose I could do that. I think I'd rather move on to matrix
displays. If I need to render only characters, I'll probably just buy
an LCD character display or something.

eBay sells big 8x8 LED arrays quite cheap.
Some of them connect together like Lego
so you can build big displays.