[H-GEN] LED display from parallel or serial port.

[Christopher Biggs]

At the meeting on Saturday,  I grubbed through databooks and price
catalogs looking for the cheapest and simplest way to build a 
group of LED bargraphs hanging off a PC.

The design goals were:

	low impact on performance of the unix box
	simple enough to build with few tools and expertise
	cheap and nasty


The SGS/Thompson 5450 chip was originally suggested as a single-chip
solution.   This is indeed quite nice, and at under $15 in unit
quantity, is cheap.   It drives 34 LEDs.    The drawback is that is a
40 pin device (difficult to wire...)

The MAXIM MAX-7219 is a similar chip that can drive up to 64 LEDs.  It
drives them interlaced 8:1, so only needs 24 pins.   It also has a
serial interface (3 wire, but NOT RS-232).   The data sheet shows how
to use it.   It /is/ conceivable that you could attach one of these to
a parellel port that is shared by a printer.  You could use this
chip to build 4 16-unit bargraphs or 8x8 unit bargraphs.    There is
also a version of this chip that has a parallel interface (easier to
program but otherwise no different).    The chip also has
software-programmable brightness control!

The chip costs $18.   64 LEDs would cost around $15.   Total cost for
this project would be about $50.   You could gang several of these
chips together for bigger displays if you wanted.

If anybody is interested, I could provide more details (perhaps even
lay out a PCB or veroboard design).


I'm also working on a design for a similar display of 8N leds (where N
depends on your budget) using TTL glue.   This will possibly be
cheaper than the MAX7219 for 64 leds, and almost certainly so for 
fewer LEDS.   It will interface via the parallel port, should be able
to share the port with a printer, and could be interfaced via serial
port or other IO source with a few extra components (possibly sharing
the port with a mouse).   

Anybody interested?

Chris.

--
| Christopher J.  Biggs | EMAIL: chris at stallion.oz.au (PGP and MIME OK)  |
| R&D Software Engineer | PHONE: +61 7 3270-4266  FAX: +61 7 3270-4245   |
| Stallion Technologies | Microsoft is not the Answer.                   |
\ Queensland, AUSTRALIA | Microsoft is the Question.  NO is the answer!  /

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