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Help me figure out these pin assignments?

Discussion in 'Datasheets, Manuals and Component Identification' started by cat6, Oct 22, 2012.

  1. cat6

    cat6

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    Sep 15, 2012
    Hey everybody,

    I picked up this component, a Rohm LU-3011 7-digit display array. You can see somebody's blog post about this component here: http://bobdasquirrel.blogspot.ca/2011/08/rohm-lu-3011-led-display-module.html

    That said, Rohm's website seems to be utterly devoid of any material (their emails bounce back and the site has almost no content) and I can't find a data-sheet anyplace.

    I can only get the first 7-segment display (on the far right) to work, and even then the top-left and bottom-right segments don't light up no matter what I do. All the pins have some effect, be it in my own experiments getting segments on the rightmost display to light up, or as noted in the blog post above. The only pins not accounted for are 7 and 20-23.

    Does anybody have any experience working with displays like this? Any hints or info are welcome.
     
  2. CocaCola

    CocaCola

    3,635
    5
    Apr 7, 2012
    Do you understand how multiplexing works?
     
  3. cat6

    cat6

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    Sep 15, 2012
    Ah, yes. I hadn't thought about that. We *just* learned about MUX's in school. Three currents enter a MUX and the third one decides which of the first two will exit. Not sure how that applies here, exactly, but I guess some further experimentation is in order...
     
  4. CocaCola

    CocaCola

    3,635
    5
    Apr 7, 2012
    Understanding multiplexing will help you understand how to light up the other 7 segments in that display... My only concern is that you said a few segments appear dead, where you using appropriate current limiting when testing? If not you very well could have damaged the display...
     
  5. cat6

    cat6

    10
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    Sep 15, 2012
    "Appropriate current limiting"? You mean like a resistor in the circuit? I've been feeding the display a 5v current from one of the digital outputs from an Arduino Uno R3. No apparent problems have come up doing that either directly or with the sort of resistor I'd use in a simple LED circuit, so I've mostly been leaving out the resistor. I've actually left this circuit in a 'blink on and off' program lighting up one or two of the segments for days at a time in between fiddling sessions--no apparent problem. And I didn't say a few segments appear dead...only that I couldn't get them to light up. I've no idea what that means--I've been assuming that I just haven't figured out the weird/mysterious electronic gizmo-der-y of the device itself. Do you think it's likely I've burnt this thing out?
     
  6. CocaCola

    CocaCola

    3,635
    5
    Apr 7, 2012
    Yes...

    Your are damaging the LEDs and they will (if they haven't already) fail shortly doing this... Shortly is a relative term, they will still light for awhile but the intensity will diminish and they will go out long before their 100,000 hour or so life expectancy... This shortened time could be a matter of seconds, minutes, hours or days in the end your are putting them in an early grave... LEDs need the current limited, review the LED sticky on this forum, running without limiting is like driving a car without brakes, perfectly safe until it's not...

    Good chance...
     
  7. BobK

    BobK

    7,645
    1,662
    Jan 5, 2010
    On the other hand, the Arduino output is probably not capable of sourcing much more current than the segments can take. But that is not a reason to omit the resistor.

    Bob
     
  8. CocaCola

    CocaCola

    3,635
    5
    Apr 7, 2012
    Valid point but AVR's are specified to be able to source/sink 40mA (I wish PICs went this high)... I have never actually tested to see what they actually will max out at before they shut down or the chip lets out magic smoke but the I/O pins have an internal resistance of 25 Ohms so they theoretically can pump upwards of 200 mA @ 5V... Even at 40mA that is a lot for a red 7 segment that generally runs at about 15mA a segment...
     
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