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Max7219 Woes — Parallax Forums

Max7219 Woes

DigitalBobDigitalBob Posts: 1,513
in General Discussion

I made some of my own 6 digit, seven segment boards. And had issues with it coming on. Such as not lighting the segments, flickering on sometimes etc.. So I added the brown 0.1uf cap. at the power pins, no cigar, still didn't work. When I soldered the blue 0.1uf cap. to the pins it works perfect. I have a previous 5 digit board and the cap. worked at the power pins. I guess thinner traces all crammed together for the 6 digit board, made for some board capacitance.

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Comments

  • frank freedmanfrank freedman Posts: 1,983

    Did you flex the board a bit after the fix to make sure no fracture or shorts of any traces? Or vias that aren't quite plated through (looks double sided). Also one hole looks really close to a trace in picture left area near the brown cap. Picture makes it hard to tell. How much mA when it was acting up?

  • DigitalBobDigitalBob Posts: 1,513

    I did a close inspection and everything look good, plus I went over the artwork again. On my next revised board I added a smt cap. Under the dip socket. Thanks for your input.

  • jmgjmg Posts: 15,173

    @DigitalBob said:
    ..... When I soldered the blue 0.1uf cap. to the pins it works perfect. I have a previous 5 digit board and the cap. worked at the power pins. I guess thinner traces all crammed together for the 6 digit board, made for some board capacitance.

    You just got lucky there :) LED drivers have high dynamic currents and certainly need good decoupling.
    Two caps are often used, eg 100nF and 10uF

    @DigitalBob said:
    On my next revised board I added a smt cap. Under the dip socket.

    Good idea
    On LED drivers it is also useful to employ the PCB CAD copper pour, to give maximal copper on both sides for heat spread.

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