I need to build a REAL sign similar to the one in this flash animation
(http://www.commonelectric.com/test.html).

SPECS:

? 5 to 6 letters / spaces (each independently lit by 1 or 2 light bulbs)
? Each letter / space will be roughly 1'6" high by 1' wide
? Each letter / space will need to flicker or flash at a random interval

The idea is to create the visual of a broken sign that is slowly begin to burn out.

My question is this... how do I do it? What's the easiest way to
create a randomly flickering light? Is there a special circuit that
will do the trick for me? Is it even possible to get the lights to act
independently of each other?

Any ideas or suggestions would be highly appreciated.

Thanks for you time.

Easiest way is to interface a computer to as solid stae switch (relay) -
 or to multiple switches for multiple bulbs.
 Either serial or parallel port can be used.
 
 You can write a program (in Basic, c, tcl ..), use timers and random numbers
 generator, and when program does what you want, 
you send the output of the program to an I/O port to control the relay(s).
 
 There are ready made interface boards on the market - so that no
custom circuit design is required.

Here are some:

http://www.electrokits.com/id-serial_port_relay_board_program.htm


SEARCH TERM: I/O port operated relay

You did not described you computer sophistication,
 so these are just few general hints on how to write to I/O port

http://www.epanorama.net/circuits/parallel_output.html

and 

http://www.faqs.org/docs/Linux-mini/IO-Port-Programming.html

it can be done is high level language, as ms (millisecond level)
timing is not an issue

http://www.hare.demon.co.uk/ioport/ioport.html

There are companies which do sell programable interface boards, intended to
control 'real devices' such as stepper motors, for example
http://www.galilmc.com/support/faq.html

If you use one of those, you can just substitude your sign for a motor,
of course, after considering proper electrical requirements for the
sign and output power and voltage requirments.

Hedgie

In the end, it looks like we're going a different route with the sign,
but none the less, hedgie's answer was timely, thorough, and very
helpful. Top notch!

Yea, could be stylish. Dead easy for electronic designers but how
techy are you? Do you need info down to the smallest detail? What kind
of lamps do you want to use, power, voltage? Cost?

Easiest with low voltage, though not quite the cheapest. Mains voltage
is easy for a designer, triacs, thyristors, IGBTs or relays, but much
more difficult for non-experts. So best to think low voltage. An
electronic designer would use transistors, preferably MOSFETs, and
though relays are conceptually simpler you?d still need transistors
(pref FETs) to drive them. Plus with relays there are ?back EMF?
concerns which you have to know about. Therefore power MOSFETs are
simplest but you still have to know something about them.

Suggest you use torch (flashlight) bulbs. Bear in mind that a cold
filament resistance is only a fraction of the hot resistance so the
PSU and FETs must be able to sustain short high current excursions.
You may have some appropriately rated transformer power supplies
kicking about. Got to be smoothed DC output to power electronic
(pseudo) random generators. You?ll find designs on the web but a
simpler, far less pseudo, generator can be built from gating a divider
chip outputs -- 4000 series CMOS being very cheap and available.

This is only the briefest of information and perhaps it?ll put you
off. Depends on if you follow what I?ve said. If most of it makes
sense to you, and you can wield a soldering iron, we can discuss to
more depth. Nice little project for a newcomer (?) to electronics.

Best

Wow, that seems like a lot of work. I'm very techy, just haven't had
much experience with solid state electronics. Thanks for your advice
though!

I can't resist... I would use LEDs for the lights and use a single PIC
microcontroller to drive the blinking lights. Very few parts, very
easy to build, but it would require a little bit of programming. There
are even BASIC-language programmable PIC microcontrollers which can be
programmed in BASIC, if you don't want to learn PIC assembly language.
Check out http://www.parallax.com/ for the "Basic Stamp", or
http://www.microchip.com for the PIC microcontrollers.

Yea as usual I agree with you gopman. Still have to sort out drivers
and PSU of course. Thought I?d spare bjork (love the singing BTW) that
route though :-)

And bjork, being techy, your learned approach should be applicable to
solid state. Do I take it that you have worked with gaseous state, ie
firebottles? On your own with these. Thankfully, germanium came along
just in time to save me too much familiarisation :-)

So shall we continue? Wish I could send pictures ?cos the circuit is
drawn in my head -- gopman?s too no doubt. Perhaps though you?d like
to ponder and come back at a later stage with proposals, or would you
like more specific device suggestions?

Just as is your pleasure.

Best

Geez - talk about using a sledgehammer.  All our friend needs is a
couple of 555 timers with a few transistors to control the current to
his lightblulbs.   Unless he's planning on performing a light show
using a computer is over kill.

Few places that have a slew of circuits at your finger tips follows:
 http://www.uoguelph.ca/~antoon/gadgets/555/555.html
 http://www.discovercircuits.com/L/lite-flash.htm
 http://www.discovercircuits.com/L/lampcont.htm
 http://www.signal-tech.com/accessories_flashers.cfm

The last being a place to purchase the control module rather than build it.

Answer Guy - If you are going to collect money for this - at least
have a clue about the problem.