Re: The need to individually switch 50 LED's

["David Buckley" <db@xxxxxxxxxxx>]

--- In ukha_d@xxxxxxx, <groups@j...> wrote:
> Hi Group
>
> I have a need to individually switch 50 LED's from a PC -
> can anyone recommend anything and how to do it?

There are numerous ways to do this, all with good tradeoffs.

The tradeoffs are money, mess, time, skills and work.

The absolute neatest way would be have a module per LED with
control, so you just run a serial bus and power round the cabinet.
Something like http://www.theledlight.com/versalux.html
but with
serial control.  A DIY version could be designed and made easily
enough, but it'll all be a bit expensive.

Distributed relay control: Use ICP relay module, four relays per
unit, I-7060, see http://www.bb-europe.com/data_acquisition.html

Relay cards in the PC, from maplins or whatever.  But you'll end up
with lots of wiring

Or you could multiplex drive the whole thing, which will reduce
wiring count significantly, but will radiate interference like a
banshee.

Wandering [OT]... I've got a thing I built years back for driving a
starcloth in a theatre, from before fiber optics became the way to
do it.  Its a 6x6 matrix driver, at 5A, 24V per line, to drive
36 "strings" of lamps, usually 5 lamps per string, for a total of
180 lamps.  Thats getting on for 1KW switching at about 25KHz,
without any supression, on lots of unscreened and untwisted wire.

Very impolite in mixed electronic company...

For KDs interest, and entirely from memory, it uses a 555 clock
driver, 2 x eproms for the matrix patterns, little plastic
transistors driving bigger driver transistors driving 2N3055s and
their complement (whatever that was)...  It also had an A/D for 0-
10V dimming control, but I cant remember how that works.  But it all
did :-)

Today I could do all the hard stuff in a PIC.  My, how times have
changed...