MK103 Conversion

I’ve built a cigar box guitar with a strand of 10 tiny ‘rice’ LEDs running inside the neck, back-lighting the fretboard inlays. The 10 LEDs were originally powered by 2 AA batteries. Now I’d like to incorporate the MK103 into the mix to make the strand of LEDs flash in-time with the music I play.

I’ve installed a 3-way turn-knob switch:
1st position - Lights ON
2nd position - Lights ON w/ MK103
3rd position - OFF

This is my wiring plan:


  1. Does the negative contact on the MK103 flow straight through the board the way that I am using it in my diagram? In other words, when the switch is in position 1 will the negative make it back through the MK103 to the battery?

  2. What could I use to reduce the voltage from 9v to 3v when the switch is in position 1?

  3. What are the output voltages on each of the four MK103 LED slots? I figure I will need to combine 2-4 of those slots to power the 3v LED strand.

Thanks for any advice you can offer. I am really excited about this project!! :lol:

great idea, here is how I would do it…
I would use a constant current LED replacing the 1 LED with four(or more if you wish)

I would connect the constant current LED as the ‘Voltage Reducer’ for when the switch is in position 1.
it might also be a good idea getting a switch that will switch the negetives as well as the positives(Eg… This one) so it can change the path of the negetive(in case it won’t go through the minikit…)

This should work…

[color=red]test it first with similar LED’s to the guitar’s, before connecting it to the guitar’s LEDs, in case this does not work…[/color]
good luck with your project,


Thanks for the reply! I did a google search on “constant current LED” and found an instructables how-to:—simplest-light-with-constant-current/

Is that what you had in mind? That looks like a great option for position 1, but i’m still left with too much voltage coming out of the MK103, right? Could I chuck the 9v supply entirely and use the 3v supply instead? Would that be possible, even if i had to change some resisters on the MK103?

Or, keeping with the 9v, could i use a voltage divider? to handle both positions?

Thanks again,

That could work, did you try the link to Maplins :

You could try running the kit on 3V, it might just work…
or you could replace the LED’s with 12V/9V ones (is that a possibility?)