32×32 panel doing nothing unless I touch a given header pin

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  • May 26, 2019 at 4:55 pm #11243
    tdelprat
    Participant

    Hi,

    I assembled the Nootropic RGB matrix backpack board V2 and connected the 32×32 leb pannel and the power supply.

    At first, nothing happened: no lights at all.

    After double checking, I discovered that if I touch one of the pins of the header connector then the panel starts to show led animations.
    In the beginning, I thought it was a soldering issue, but it does not seem so:

    • this happen with only one pin
    • just barely touching the pin is actually enough>

    Based on the schematic, my understanding is that this is the pin connected to the 5V supply:

      x x
  x x
  x x
  x x
  x x
  x x
  x X   <- pin than when touched makes the panel work
  x x
--   -- 
  [ ]   <- push button
--   --

    I double checked all the soldered parts, I believe this is not the issue.

    My current understanding is that I have 2 different issues:

    Sorry if my questions are stupid, I am a beginner.

    I welcome any hint or advice.

    Tiry

    • This topic was modified 5 years, 6 months ago by tdelprat. Reason: updated formating
    • This topic was modified 5 years, 6 months ago by tdelprat. Reason: updated formating
    May 27, 2019 at 5:47 pm #11250
    Michael
    Keymaster

    Hi Tiry,

    Hmm, this is strange. I seems like there is a bad connection between the backpack board and the matrix. Sometimes the male and female headers don’t make good contact, and a very light touch may help. It may be the ground pin that has a bad contact, too.

    I would try this: remove the backpack from the panel. Then carefully bend the panel’s 5V and ground pins a small amount. This way when you connect the backpack it may make better contact. Sometimes a very small adjustment to the position of pins will help.

    That’s my suggestion. It sounds like you soldered it fine, and if it is showing animations (even the wrong size for the display), then that means that the backpack board is running correctly. I think you have a small connection problem. Let me know if you get it working.

    May 29, 2019 at 5:34 pm #11260
    tdelprat
    Participant

    Hi,

    Thank you for your answer.

    Switching the power supply for a “switching power adapter” did not solve the issue.

    I did not succeed in solving the issue by bending the pins or unplugging / plugging the backpack card.
    It does not seem to be a pressure issue.

    To be clear, even barely touching the 5V pin (on the backpack board) indicated in my previous post makes the panel work (or at least do something).
    It does not work if I touch with plastic but works if I use my finger or even paper(!).

    As I said, last time I did electronic was about 20 years ago and even back then I was a beginner: it seems to me like something related to power supply or ground, but I obviously may be wrong.

    Any other advice for me?

    Thanks.

    Tiry

    May 30, 2019 at 12:14 pm #11274
    tdelprat
    Participant

    I realized that I was looking at the schematics on page https://nootropicdesign.com/matrixbackpack/design.html whereas I have a V2 board.

    So, I installed Eagle to be able to view the V2 schematics.

    It seems that the “magical” pin that makes the board work when I touch it is not connected to 5V but to what I think is the PIN 16 (PB2 ?) of the ATMega328.

    Not sure if this help or even makes any sense …

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