Hello!

I’ve ventured far too deep into the custom ergonomic columnar-staggered mechanical keyboard rabbit-hole, and I think I’ve finally found myself at my endgame (for now, anyway lol): the Hillside 46.

TL;DR:

Please see “questions” section at the bottom regarding why, how, and if I should use the ESD protection on the right-half, left-half, or both halves of this split ergo-mech keyboard build.

Background:

In constructing this board, I came across a part of the circuit design that has confused my non-expert brain: the ESD chip and decoupling capacitors. At a theory level, I understand that it protects the board from electrostatic discharge (presumably, specifically, the microcontroller) and the damage it can cause. What is weird to me is that this is the only keyboard out of the several split-mech-ergo boards I’ve built that have featured this protection circuit, and even within the Hillside family of keyboards, the version with 46 keys that I built seems to be the only one with this protection circuit which makes the decision even more perplexing to me.

Given that this is a split-keyboard design with a reversible PCB, there are footprints for the SRV05-4 ESD chip (datasheet here) and decoupling capacitors on both sides of the PCB though they appear to be wired up differently depending on the side of the board you’re using (schematic here). On the “top” of the PCB (left side of the keyboard), you would solder the ESD chip with pin 1 at the top-left position. I did this and everything works fine.

On the “bottom” of the PCB (right half of the keyboard), the connections to the pads seem to be mirrored from the “top” of the PCB, but it looks like that was done so in a way that would not allow me to invert the ESD chip, with pin 1 at the bottom-right of the footprint, and still have everything work. I definitely can’t keep pin one at the top-left of the footprint on the “bottom” of the PCB, so I’m kind of stuck as to what to do.

Questions:

1. Are the ESD chip and decoupling capacitors necessary or just nice to have?
2. If they are necessary or very useful, do I really need them on both halves of the board?
3. Looking at the Gerber file, it seems like I might be able to mount the ESD chip to the footprint on the underside of the right-side PCB and still have it functional; is that correct?
4. What is this ESD circuit protecting against, exactly? I assume it’s potential voltage spikes on lines that shouldn’t have them that can occur if I were to unplug one end of the audio cable while the keyboard was still plugged into power/USB; is that correct?

Thanks in advance!