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Ribbon cable length causes noise for displays why?

Discussion in 'General Electronics Discussion' started by willwatts, Nov 15, 2014.

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  1. willwatts

    willwatts

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    Ribbon cable length causes noise for displays why?
     
  2. davenn

    davenn Moderator

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    specifically what sort of noise are your referring to ?
    what are the symptoms ?

    longer unshielded wires will have noise induced into them
     
  3. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Or radiate it.
     
  4. davenn

    davenn Moderator

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    indeed ! :)
     
  5. willwatts

    willwatts

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    specifically what sort of noise are your referring to ?
    what are the symptoms ?


    Display noise on the LCD readings

    The Seven segment displays red lights have noise on the readings

    Are Ribbon Cables not shielded? what else can I use instead of ribbon cables for displays like LCD and Seven segments displays?
     
  6. willwatts

    willwatts

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    Either reflections/impedance mismatch (signal integrity)

    An Impedance mismatch between the circuit boards impedance and the displays impedance?


    or degrading power rails due to the resistance/impedance of the cable (power integrity).

    The ribbon cable adds resistance and lowers the power rails?
    How would lowering the power rails add noise?
     
  7. Gryd3

    Gryd3

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    If the voltage drop is too high along the cable being used, it can induce noise and other ill symptoms... microcontrollers and other logic will not operate in an expected manner if it's power source is excessively noisy or too low.

    Keep in mind too, that any cable will degrade the signal as the length increases. Some cables do better than others depending on the conductor quality and shielding. If there is poor shielding you run the risk of picking up noise from other sources, or even something called cross-talk where the signal from an adjacent wire leaks over. The display noise could be caused by a number of things.
    If possible, you can slow down the data transmission rate if the display supports it, as slower data speeds will usually resist being degraded over longer cable runs. This does not help combat picked up noise from other sources though.
     
  8. willwatts

    willwatts

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    Nov 15, 2014
    What are some common LCD displays noise problem causes?
    What are some common Seven Segment display noise problem causes?

    Instead of using a ribbon cable, what can I use for displays?

    If the voltage drop is too high along the cable being used, it can induce noise and other ill symptoms

    Why does this happen when the voltage drop is to high?

    The length of cable is resistance
     
  9. willwatts

    willwatts

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    Nov 15, 2014
    Does LCD displays or Seven Segment displays cause more noise problems? which one cause more noise problem issues?
     
  10. davenn

    davenn Moderator

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    you still haven't told us what the exact noise problem is ?

    you said that but it doesn't tell us anything much. Tell us the exact symptoms

    and whilst you are doing that
    also tell us where the ribbon cable is in the circuit. Is it between the driver IC's and the display(s) or somewhere else in the circuit ?

    if you don't get to the point quickly I will close the thread again
    I'm not going to let it roll on for dozens of posts going nowhere
     
  11. Gryd3

    Gryd3

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    OK. lets clear this up...
    Noise is caused by external factors such as WiFi, microwaves, Solar Flares etc. This makes it difficult to properly interpret the commands/data being send on a wire if too much is picked up. To help with this, you can shorten the wire, or shield it from the noise by using twisted pair or shielded cable/wire.
    Signal degradation is caused by the wire carrying the signal... if the signal path has too high a resistance, inductance, or capacitance it can alter the signal to the point where it can no longer be recognised.
    There is a third kind of half-way between the two... the signal itself can cause a reflection in the conductor where there are poor electrical connections or impedance mismatches... these echoes interfere with the signal much like noise does... then there is cross-talk where the signal from one wire leaks into another which again, will function like noise.
     
  12. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Oh, and willwatts, whist you're doing that, LEARN TO USE QUOTING.
     
  13. willwatts

    willwatts

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    Nov 15, 2014
    So Ribbon cables are not shielded? what multiwire wire can i use like a ribbon cable to connect to "headers" on a PCB that is shielded?

    I think it's before the Display drivers, what circuit is before the display drivers called for LCD and Seven Segment LED displays?

    7 Segment LCD VS 7 Segment LED:
    which one causes more display noise issues? from ribbon cables? or other noise issues?

    Some displays need a voltage doubler circuit that goes to the display

    what kind of voltage doubler are used? and what kind of displays need a voltage doubler?
     
  14. Gryd3

    Gryd3

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    You should really be reading up on noise, cross-talk and signal attenuation on wikipedia.

    anyway... one method of reducing / eliminating noise is with differential signalling... This is the signal that gets passed down the line, but requires two wires to pass a signal that one wire could typically do.
    You ask what wire you can use... but don't offer any proposed use... where will it be connected, how long do you want it to be, what is the display it will be driving, what data-rates are you planning on using?

    ... the 7 segment LCD/LED question you have posted is making me re-evaluate my time spent typing ... You really should learn to google around a little bit, as it seems apparent to me that you do not understand the concepts that are being discussed.
    Can you please explain why you would use an LCD instead of LED, can you provide any details regarding one over the other?
    Are you aware of the function of a voltage doubler? If your battery was a high enough voltage, would you still need one?

    I am glad to help work though problems and to help people learn, but I need to determine how much you currently understand about the subject and if you have enough interest to look for information from other sources.
    Please do your best to answer the questions provided and we can work out some more of your specific questions...

    (Also.. I am unsure why you are so hung-up on ribbon cables... they have been commonly used in computers, and are still present in cellphone, tvs, and many other displays without any issues.... of course, learning how you want to use it would help)
     
  15. willwatts

    willwatts

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    Nov 15, 2014
    I'm not sure why some company's circuits use LED displays and other Company's circuits use LCD displays
    what I mean is the display issues they have over the other
    can you list some common problems and issues LED displays have compared to LCD displays and vise versa?

    It takes 5 volts lets say and doubles it to 10 volts

    No

    But my question was which displays use a Voltage doubler? i know what a voltage double is and does , i don't know which display types use a voltage doubler

    To power up the display and back lights
     
  16. davenn

    davenn Moderator

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    I don't know of any displays that use a voltage doubler

    LCD displays need a back light its provided in one of 2 ways
    1) low voltage white LEDs
    2) high voltage (1kV - 3kV) CCFLs

    neither use voltage doublers. The CCFL lamp system uses an oscillator and small transformers to generate the high voltage

    Dave
     
  17. Neal

    Neal

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    I think the electric chair uses a voltage doubler:eek:
     
  18. davenn

    davenn Moderator

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    hahaha don't wanna go there :p
     
  19. willwatts

    willwatts

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    Nov 15, 2014
    list the display types
    1.) LCD
    2.) LED
    3.) what else

    what is the circuit before the Display drivers called? what circuit drivers and goes into the display drivers?
     
  20. davenn

    davenn Moderator

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    3) ... VFD ( vacuum Flourescent Display)

    who knows .... what ever the designer wants ... maybe a counter circuit
     
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