The front PCB that screws into the front shell and has the button pads on the board has a BU5782K ASIC that handles headphone audio and button presses.

Button Interface

Here is a quick TikTok explaining the button interface/

Buttons are polled every 33 milliseconds.

The read trigger is a 1us pulse that happens on pin 7 every 33ms.

Each pin has four states.

1. No Buttons Pressed = 5V DC
2. Button A Pressed = 5x Low Pulses 13us apart
3. Button B Pressed = 5x High Pulses 13us apart
4. A + B Pressed = 0V DC

The pulses happen as soon as the Trigger (pin 7) pulses high.

Here is an example of the pins 9 down to 2 from top to bottom. with Left and Run currently pressed.

As you can see pin 7 is the main trigger pin when buttons are read. Pin 6 is a pulse map (the times at which the button pins toggle into the same pattern or inverse pattern.

Then pins 2 to 5 are dual buttons (2 buttons per pin).

Front Board Ribbon Pins



Button Presses

The trigger pin 7 goes high, and then the four button data pins (2 to 5) are read in right at that moment.

Take pin 2 for example which is Up and I buttons.

Without anything pressed the blue pin is 5V.

If Up is pressed, then pin will output the pulse map but inverted.

If I is pressed, then the pin will output the pulse map non-inverted.

When both Up and I are pressed, the pin will go to ground.

Toggle Sliders

The I and II toggle sliders on the front are turbo buttons. They have 3 positions, left, middle and right.

The left position is off, the middle position turbo presses (repeat press/release cycle) while the respective button (I or II) is held down, 4 presses on, 4 presses off, so 132ms on, 132ms off or approximately 4 times a second.

The right position is twice as fast so 2 presses on, 2 presses off, (66mm + 66ms = 132ms) and approximately 7 to 8 times a second.