pouët.net

Hi guys,

Suppose I wanna do some demofx on a led matrix, can some of you 'electro' guys advice me a nice starting kit?

Keeping in mind that :

- I can solder jack cables, but I rather don't wanna solder at all
- I prefer something 'premade' with an RS232/USB/whatever connection
- I wanna spent most of the time on writing code
- controlling of min. 8x8, preferably more

I've read numerous articles explaining about charlieplexing leds, schematics, but this stuff is way out of my league.

i'd assume unless you wanna go expensive, some soldering will be inevitable - perhaps hooking up with someone who cares less about code but much rather tinker the hardware might be a good idea.

Most of those VFD/LED scrolling message displays can be programmed over rs232, some allow you to define custom graphics chars but it's not likely you will find one that lets you address pixels directly.

Here's a datasheet for a vacuum fluorescent one that looks like it lets you address pixels as 1 byte per 8-pixel column: http://www.farnell.com/datasheets/90768.pdf (farnell code is 1172812). Haven't found an LED one similar but VFD is brighter anyway.

You want to pay attention to the update speed though. That Noritake one will run at 19200 baud, which gives you a potential maximum refresh rate of 20 FPS (no doublebuffering as far as I can tell). At 9600 baud the refresh rate would drop below 10 FPS (that is if you can even transmit a bitmap image and won't have to redefine the font and build the image out of custom characters).

looks like you could get higher framerates by skipping unused columns using abs/rel column set commands.

Damnit now I want one of these.

ah...too bad.
I think I'll rest my case.

some last thoughts :

Check this, the nowadays price for a 180 led (RGB!) is 16 dollars.
Somebody should document a 'DIY christmas light into usb controlled led matrix'
So basically if someone could figure out to hack the controller..

http://www.dealextreme.com/details.dx/sku.16777

about the price :

the led themself doesnt cost a lot of money

here ten 8x8 led matrix for 6.9 € :

http://cgi.ebay.fr/10-Matrices-8x8-Points-64-LEDs-Rouge-2V-5-10mA-NEUF_W0QQitemZ150313982568QQcmdZViewItemQQimsxZ20081204?IMSfp=TL081204122001r25676

and i think you really need soldering at all using this kind of stuff :



for the display



you dont neep to buy special chip. you can use a pic (easy to program , have its own rom+ram, very cheap) that will do all the work

basically it will do this :

output 8 bit char (to set the current row of led) + a 1bit (that is set from 0 to 1 periodically to select the next row (you will need a johnson counter to achieve this).

it will set one row of led at a time for example for a two 8x8 blocks you will need 16 clocks

maybe its possible to output two bytes at the same time with some pics (thus a full 8x8 block is set directly), then you dont need additionals chips (like the counter) but if you want to use multiple 8x8 blocks then it never be enough (for eg a pic cannot output 64bits at the same time)


the good thing with this :
-cheap design
- you'll have full control of the led pattern , not only show 'a' or '!'
- most of the stuff rely on program inside the pic

mmm seems some people post a lot of stuff while i was writing....

That certainly isn't to his specification, but it is what I would've done.

And those twinking christmas lights aren't independently addressable, the controller will usually just dim/undim two or three banks of LEDs to make them twinkle.

outsource it to India..