SOLVED!!! ~ mk LED troubles - ghosting LEDs

  • hey all

    so i have my mk128 almost finished but i have run into a weird problem that has me a bit confused. when i run monome test and trigger the LEDs, i get ghosting on other LEDs in either the same row or column. the ghosts are never in the same arrangement and only exist on the same button PCB. i tried resoldering everything but no avail. there are a few cold solder joints on the diodes i am going to re-do now but has anyone run into this problem or have insight as to what it may be? i figure it is probably something easy and involves a longer time with my soldering iron, i'm just not sure yet. beh?

  • Check you have the correct r set resistor. I used one that was too low and i think it was overloading the led driver to light additional led's.

  • not the iset? i used the included one, however my LEDs are a lot brighter, still they operate at the same settings.

  • oh, and for further info, all the button presses are fine, so it appears to be a problem solely with the LEDs

  • What LEDs did you choose? Were you going for mega bright! Did they go outside of these gudlines?

    http://docs.monome.org/doku.php?id=tech:mk:led

    I have not built one of the new kits but the theory is the same. The I-Set resistor controls the maximum potential current to the MAX chip. If you install LED's of a value that is too high drawing too much current, it will not be happy. I really no very little about electronics but when I checked the value of my resistor, it was all wrong. I changed it and happy days.

    http://www.arduino.cc/playground/Main/MAX72XXHardware

    Have a look at this link. Scroll down the bottom. It shows how to calculate. Looking at the driver kit, I think this table will help you calculate if you have gotten a bit carried away with your LED's.

  • ghosting indicates a fried max chip.

    typically this happens when the iset resistor is too low. seeing as how you used the provided resistor, it perhaps was defective from the factory, or it was overheated when soldering.

    you should be able to swap a new on in. let me know if you have problems, i did one last week by removing it by cutting the legs, then cutting the legs off a new chip (thin part only) and "surface mount" soldering the leg-less one on there. worked well.

  • is this chip more sensitive to heat then others? because it is happening on both of my boards, so this problem would have happened twice. if that's the case it's possible i overheated that chip twice, or, it is the iset resistor. which should still be ok since my LEDs were 20mA and 3.2v. there luminance is a huge 6000mcd though!

  • what kind of soldering iron are you using? does it have temp regulation?

    twice seems bizarre.

  • yea, that is why i am questioning it.

    it's the weller wtcpt, temperature controlled tip iron. i'll try replacing the tip and try it again. it probably won't hurt to up the iset to 20k huh? though that seems to not have been the problem...

  • those chip's are pretty robust. For the sake of a resistor, i would try a higher value. You have gone for quite bright led's and i would suspect the data sheet for them is not correct. It really sounds like the same issue i had.

  • Problem solved ¡!!!¡!!¡¡¡¡!¡¡!!

    Replaced all leds and no problem. Even though it worked on my ardiunome, DONT USE LEDS FROM EBAY!!!!!