Re: Controlling hundreds of LEDs

From: Si Ballenger (shb*NO*SPAM*_at_comporium.net)
Date: 12/21/04 

Date: Tue, 21 Dec 2004 19:33:22 GMT

On Tue, 21 Dec 2004 17:41:22 +0000, Danny T <danny@nospam.oops>
wrote:

>Hi All,
>
>I'm trying to control hundreds of LEDs from my parallel port (8 data
>pins - will soon be replaced with the output of a programmed PIC, also 8
>pins).
>
>I'm not an electronics guy (I'm a software developer), so trying to
>control x00's of LEDs from 8 pins looks a bit tricky...
>
>There's no way to change them all at the same time, so I reckon I'll
>need some sort of "addressing" system. Using some of the pins to select
>which LED I'm controlling, and one for the data.
>
>Trouble is, even using 7 bits as the "address", I've only got 128
>channels, but I imagine I'd need a bit for "send" too, so I can set the
>address and the data, then have it read in one go.
>
>What are my options? And what components would I need to achieve
>something like this (I imagine right down at the end, I'll need a number
>of registers for the LEDs. If these come in chips with 8 output legs, I
>guess I'll need 38 for 300 LEDs. The bit between my 8 data pins and the
>computer isn't my area though, so I'm stuck!
>
>Oh, and this is just a hobby thing, so the cheaper the better. I'm sure
>I can already buy scrolling screens, but I don't have the money, and I
>want the fun of building one! :)
>
>--
>Danny

The below link has some info on individually controlling 320
christmas light strings via the parallel port. These could just
as well be LEDs. To turn on/off an LED will probably take an NPN
transistor and two resistors per LED instead of using a relay.
You've actually got 12 pins on the parallel port to work with.
The bottom links are some pages I've made with some simple
parallel port setups. I like tinkering with the 74HCT259 chips,
as they demultiplex and also latch, and cost only $.40 each. You
could use the 4 control pins to select the 259 chip pin and set
high/low, and the 8 data pins to control other 259 chips that
would individually clock the selected 259 chips. Get a couple
chips working as a test, then expand from there.

http://computerchristmas.com/index.phtml?link=how_to&HowToId=4

http://www.geocities.com/zoomkat/output.htm
http://www.geocities.com/zoomkat/ppswitcher.htm
http://www.geocities.com/zoomkat/status.htm
http://www.geocities.com/zoomkat/files/zoomkat-lpt.txt

Relevant Pages

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