This is my first instructable.... ever. So here it goes.
I own a Kaossilator 2 (KO2). It's fun little phrase synthesizer and simple looper. But it has this awkward issue with mic button. When you want to record something from microphone you have to hold down two buttons simultaneously. First the mic button to enable built-in microphone or external input (mic in) and second the loop recording bank button. This isn't an issue until you want to connect another instrument to it and record a loop. While holding down two buttons you have only one hand free to express your self as best as you can.
Imagine that mic enable button is toggle switch. You could enable external input and hold down bank button with your foot and have both hands free. We are now one step closer to our goal. But you still need to put KO2 on the floor, record a loop and then pick it back up. This calls for an foot switch which I'll be making in my second instructable.
Since Korg is reluctant to incorporate mic input toggle functionality in software update this could be solved with a little hardware hack. There are many ways to latch a push button. It can be done with transistor circuit, logic gates, NE555 timer or an microcontroller (MCU) and probably some other ways too. My favorite is MCU since it uses least amount of components and can be soldered directly on KO2s PCB.
Step 1: Look inside
First off let's see what we are dealing with.
We see a nicely exposed signal line from SW7 to some resistors. This is a signal path of our mic button. Since there are no other components in the way we can just break the line and solder our MCU directly on the board.
Next thing to consider is that big black chip. Finding out functionality of its pins is important for tracing out the circuit. In our case the only pin that concerns us is Vdd 3.3V power line for our MCU.
Link to CY8C3244AXI-153 PSoC: http://www.cypress.com/?mpn=CY8C3244AXI-153
In datasheet we see that closest Vdd pins to our line are 26 and 100. And GND is everywhere. Entire mesh is GND.
So now we know where all of the signals that concern us are located.