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Understanding the Brain Jr Led Matrix

edited August 2013 in Hardware

I have successfully connected 18 button switches(16 to digital and two to analog ins)  and 16 leds to the dedicated led pins of the brain Jr.
Everything works well and i'm very pleased so far !

But i can't figure out if it's possible to connect two more leds to the brain Jr withe the "led matrix" thing to also have led indicators for switches 17 and 18 ?
I read the wiki a few times but i really don't understand the led matrix stuff.
I would be grateful if someone can walk me through the process of figuring out how to connect leds 17 and 18.
I'm not using RGB leds.
Thanks !



  • You can connect LED 17 to +1 and -2, and LED 18 to +1 and -3. Then they should be ID 1 and 2 in the editor.

  • Ah thank you mark, it does't seem too complicated when put like that ! :-)

    i realise my leds 17 and 18 are close to leds 7 and 8 so for pratical reasons i might try using pin +7 and -8 for led 17 and pin +8 and -7 for led 18. Do you think that will work and how do i find them in the editor ?


  • If you imagine RGB table on the wiki as a table for connecting single LED's and forget that they are grouped in threes, you can find the combination you are looking for then just count. For example +7, -8 would be LED 38 (ID 37).

  • Thank you very much for your help, it is working !
    Finally, i installed RGB leds to have more options.

    The only problem is the red side of leds does not turn off completely.
    Though it serves as a USB voltage indicator light ... lol


  • That is a known problem that we are working on. The red color on that RGB led has a low threshold voltage and therefor does not turn off completely. You cannot see it through the rubber buttons if you are using those.

  • Unfortunately i'm using transparent lens for the led so it's very visible.

    Is there a chance this can be corrected by firmware update or is a new revision of the circuit board required ?


  • Maybe there's a specific type/brand of RGB 5mm common anode diffused leds that i could use and be sure the red forward voltage is high enough  ?

  • All three things you have proposed are possible solutions. We will be correcting this issue on the next run of boards if we have not already produced a firmware fix.

    I'll update this thread as more information is available.

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