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  1. #31
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    Re: 7 segment led displays and my Radio Box

    The reason for your displays not to work as expected , when chained on the same power line is the fact that each device when works and consumes power, it creates noice too to the next device down the chain.
    If you need to chain multiple displays to a single 5v power supply line, using small ceramic decoupling capacitor ( 100 nF or more ) btw 5v and gnd wire , as close as possible to each device, might help. It 'de-couples' devices not to be dependent on each other when they consume power. It might need some experimentation with bigger capacitor values, as your display + cmos package uses much more power. As a rule of thumb – it is best when you combine biggest possible capacitance in the smallest possible package and put it as close to the chip as possible ( smaller capacitor package means less internal resistance and faster response). Additionally –add a bigger electrolytic capacitor 5 uF per device approx ( if you chain 6 displays - 6 x 5uF = 30 uF ) in the beginning of the chain , next to the voltage regulator.

    That might help to some one experiencing similar problems in the future.
    Good luck.

  2. #32
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    Re: 7 segment led displays and my Radio Box

    Hi trakon,
    These MAX7219-driven 8-digit 7-segment LED modules that I am using already have a 100 nF de-coupling capacitor on board, and the specs say upto 8 of them can be daisy-chained without the need for any other elements, so their non-performance in this regard may probably be due to other issues.
    Regards,
    Chakko.

  3. #33
    300+ Forum Addict Tom_G_2010's Avatar
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    Re: 7 segment led displays and my Radio Box

    Quote Originally Posted by tomahawk66 View Post
    Hi trakon,
    These MAX7219-driven 8-digit 7-segment LED modules that I am using already have a 100 nF de-coupling capacitor on board, and the specs say upto 4 of them can be daisy-chained without the need for any other elements, so their non-performance in this regard may probably be due to other issues.
    Regards,
    Chakko.
    I've found that almost every stability problem I've had with them was related to power and daisy chaining. In most cases I was able to chain as many as four but not always. Sometimes they just got finicky. In the end I decided to run a parallel power bus and all was solved.

    I haven't moved any of my projects off the test bench and into permanent enclosures yet but when I do I'll be powering them on a bus to be sure I don't have any problems.
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  4. #34
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    Re: 7 segment led displays and my Radio Box

    Hi Tom_G_2010,
    I did run a parallel +5V / ground power bus off my regulated DC power supply, and connected the VCC / GND of each of these modules individually to this, but that did not solve the problem; I got fully lit displays and/or blank displays, and/or overheating MAX7219 chips. Would you be able to post photographs or a diagram of exactly how you connected your module pins to this bus?
    Thank you!
    Chakko

  5. #35
    300+ Forum Addict Tom_G_2010's Avatar
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    Re: 7 segment led displays and my Radio Box

    I'look to see if I have an photos that are clear enough, but most aren't as this was done on a test bench with pin jumper spaghetti of epic proportions.

    What you describe though for your power bus sounds like what I did as well. On the flip side do you have a connection diagram you can share?

    Also, as this is starting to get off topic from the original thread it might be best to start your own new post. Just a thought.
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  6. #36
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    Re: 7 segment led displays and my Radio Box

    It is good that you have 100nF capacitors pre -installed . And the power supply is regulated - as it should be . But the thing is - the power supply is too slow to react fast enough to the rapid changes in consumption. Still -there might be a need from a 22 uF electrolitic capacitor in the beginning of the power line - if that doesn't help, then i give up.

  7. #37
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    Re: 7 segment led displays and my Radio Box

    Quote Originally Posted by Tom_G_2010 View Post
    On the flip side do you have a connection diagram you can share?

    Also, as this is starting to get off topic from the original thread it might be best to start your own new post. Just a thought.
    I've attached rough drawings of what I understood was suggested, and my working solution. I should add that my Arduino Mega 2560 draws its power via the USB connection to the PC.
    I think we're still within the topic of the thread, which is specifically about interfacing these very modules with Arduino.
    Attached Images Attached Images

  8. #38
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    Re: 7 segment led displays and my Radio Box

    Hi Tomahawk66, did you try a wiring , where Arduino and External source share common GND :

    SuggestedCascade.jpg

  9. #39
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    Re: 7 segment led displays and my Radio Box

    Hi trakon,
    First, thank you very much for taking so much interest in my little puzzle.
    I did try your suggested configuration before, and it did not work, but to be sure I retried it, and found that one or the other of the 4 modules would arbitrarily power off after about a minute. Only restarting Link2fs brought them to life again.
    Would it be possible for you to show me on my diagram how exactly I would connect the leads of the 22 uF electrolytic capacitor you suggested, in order to block the noise? I understand what you are telling me about the susceptibility of even a regulated dc supply to fluctuating power demands and would like to get to the root of this problem.
    Thank you again for your time and patience!
    Regards,
    Chakko

  10. #40
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    Re: 7 segment led displays and my Radio Box

    I am interested by this subject, because just like you i am trying to find the best way to power displays from an external power supply ( those displays are too hungry for power after all) My displays are not 7 segments, they are ordinary 1602 and de-coupling capacitors worked for me ( most of the time )

    SuggestedCascade.jpg

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