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Hardware

LED displays with Linux? 21

Timothy asks: "It seems that everywhere I look I see articles about Linux/chickenwire based MP3 players for cars that utilize a LED display instead of an actual computer screen for outputting track information and such. My question for you is simple: where can I find information on buying/using a LED display in Linux. Where can you buy them, what's an average cost for one (so I could gauge what's listed)? Would it hook up to a serial/com device? Do you need a special card to interface it into a computer system? How would you go about writing information to the LED and such?"
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LED displays with Linux?

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  • by Anonymous Coward
    I built one awhile ago. It is really simple.
    If all you want is to control 8 LEDs then
    it takes about 10 minutes using hte parallel
    port. If you want more then its still pretty
    easy w/ a microcontroller.
    Check out

    http://www.hut.fi/Misc/Electronics/index.html

    on that site are a couple PC circuits that use leds that are very easy!
  • I have interfaced Linux with a Pro-Lite LED Sign Board for use as a message board at a radio station. The interface is Simple! It connects to the computer via a serial port and accepts simple ASCII character commands for programming. In fact, you can go to their website and register to have them email you the ASCII command set. It seems to work great! If you need more information , write me at andrew.bunker@ksl.com
  • A quick trip to Google revealled the Linux Router FAQ (http://www.linuxrouter.org/faq/LRP-FAQ-2.html) has some links at question 2.21 to the software and all. A few clicks around them, I wound up at www.linuxcentral.com which has them starting at $58.95 for a 8 character wide, 2 line display.

  • Wow.. I wrote that LED-stat.txt file back in '94, and I'm amazed people have used it for this kind of stuff.. My contribution to open source, before it was called open source :^)
  • You see those scrolling (sometimes multi-color) LED signs in shops, banks and airports. A couple of these hanging in a few rooms would make for some excellent notification devices and probably wouldn't take much on the computer-end to use.

    Has anyone spent time using these? Where could I get a few cheap ones?
  • hey-- this loadmeter and heart beat meter sounds very nice -- do you have a web page describing it somewhere?

  • i think i have a program somewhere to put your own message in the little box. i have to look around for it. int 11h or something. we wrote little pascal TSR's that wrote things like "THIS IS A VIRUS" to the little display on school computers. it was fun.
  • No. (This was a couple of jobs ago. Somebody else that worked there actually did the coding for that and the actual interesting bit was the control of the relay hooked up to the NT box's reset switch. We never put it on a web page or anything like that. I'd be surprised if anybody still had a copy of that code, too)

    It should be a fairly easy modification to the ledstat program, though.
  • by Falsch Freiheit ( 7780 ) <`moc.liamg' `ta' `tiehierf'> on Wednesday May 12, 1999 @10:50AM (#1895567) Homepage
    LEDs are 'Light Emitting Diodes', the most common choice for any little blinking light on your computer (they tend to be just a little colored light.)

    LCD is 'Liquid Crystal Display' which has this liquid crystal that's polarized and changes polarization when some electricity is run through it. This is what's used on digital watches, calculators, laptop displays and the little linux based MP3 player thingy that I've seen before.

    If you're interested in the former, look on metalab (ex-sunsite) under Linux/system/status [unc.edu] you'll find that there is a led-stat.txt describing a short program and cable with LEDs, etc. (there's also a ledstatus tarball and lsm) You can modify this LED status program in a number of ways, at one place I worked we had it set up with a colored "load meter" (gets higher when more load) combined with a heartbeat (goes back and forth to give you a 'feel' of how much CPU is available) and with two of the parallel port pins hooked up to a relay hooked up to the reset switch of the NT machine next to it, so we could send a specific signal to lcdmeter and reboot the NT machine when it froze.

    If you're interested in an LCD display panel, as I suspect you really are, Matrix Orbital Corporation [matrix-orbital.com] makes a series of LCD display panels (also VFD (Vacuum Fluorescent Display) modules that appear to be completely compatible and brighter than the LCD panels) that are sold through a few different channels, including Linux Central [linuxcentral.com]. These appear to use RS-232, (or I2C, whatever that is) so you'll need a spare serial port.

    The software to drive these is LCDproc [omnipotent.net] which works on a fairly configurable client/server interface, so it should be possible to display anything you want with LCDproc as long as you can write a client that can speak the protocol [omnipotent.net].
  • You can check to see if it's on the SMB bus. I know some displays use the SMB bus as it's an available communications link, and standard chips are available for it. There is a group working on code for monitering CPU temps and system voltages via SMB connected devices already installed on many motherboards. I just couldn't find it on a quick search.
  • I've looked into making them, and the main cost is the LEDs them selves. For high brightness LEDs your talking $1 a piece in 1+k quantities for red @ 1cd light output. If you want full color, look at $4 per led with much reduced visibility, or $12 for simular visibility to a high brightness red. Prohibitive. One could setup a Linux box behind one of the displaies to run it without much fuss. Just use an IO card and latches, or the parallel port with latches and addressing logic. A hint, don't try to control more than 8x8 squares at once unless boosting your sink/drive currents.
  • If you're looking for a cheap way to get an LCD running on your system, check out the Sanyo DM016Z at this place [eio.com] (scroll down-near the bottom). It's a 2x16 character backlit LCD that uses the industry-standard Hitachi HD44780 controller for only USD $5.99 + S&H. You may also want to purchase the lcd cable for $0.99 if you want to make life easier. There are also links on the page to schematics to show you how to connect the device to a parallel port or serial port.
  • I have one of the old everex 486 computers that have a little led display built on them. I was wondering if anyone has figured out how to control them. The are 8 characters wide. When in dos they say stuff, but after lilo loads they say "EXE BOOT". When reading floppies in dos they tell you what track they are reading. I think they are controlled by bios calls, but thats all the information I have. Anything someone could give me about controlling them would help. Thanks.
  • Yes that file was quite influential, I think. It made me hook up a nice 8 bar LED to my parallel port. I even hacked together a kernel module, and some interesting driver software.

    Hmmm, I should get that back to working order (I guess the kernel module will need some reworking though. It was written on a 1.2 kernel I think ;)

    And I still think that >$50 for those LCD modules is a bit steep. I think I'll have a look at our local electronic store, and see if I can't find anything way cheaper...

    Regs, Pierre.
  • I, as do many Linux users, venture to the dark side from time to time (Mesa support for TNT would change things dramatically, though). I read LCDproc's faq on a windoze port, but I'm not holding my breath. Anyone know of a place to find some software for an LCD screen (free would be nice, I suppose)? hotfiles, download, & winfiles came up with a bunch of nonsense. I'd just hate to spend 100 bucks or so and have is sit there looking dumb in windoze (M$ insult explicitly implied).

    Monty
    (I blame everything on nvidia lately)

  • I have a Matrix Orbital display, 4 lines by 20 characters. The one I have came with a bracket that fits in the drive bay.

    You can display anything you want on it just by writing to the serial port that it is plugged into. I wrote a perl script to play around with it. It has some control characters for positioning text and doing bar graphs. Pretty neat device.

    LCDproc is a program that will display proc info to these panels. It is cool too, but not neccessary if you are using it for a specific application like the MP3 players.

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