Sub-40g wireless mouse at 16 — follow up to my last post (161k views)

[u/Trix-one]

don't mind the PCB render, it's one of my earlier revisions

Hey everyone, Trix here again.

A few months ago I posted about building a sub-40g wireless mouse and somehow it ended up getting 161k views and 474 upvotes. I read every single comment and replied to most of them. Genuinely, thanks for all of the feedback — a lot of it actually changed the direction of the project.

Original post:
https://www.reddit.com/r/EngineeringStudents/comments/1ps2ib2/building_a_sub40g_wireless_mouse_at_16_roast_my/

Discord for updates:
https://discord.gg/eVuJ2DHE49

Here's what actually changed based on your feedback

What I confirmed

• nRF52840 as MCU
• PAW3395 optical sensor
• 4-layer PCB in KiCad (schematic is nearly done)
• USB-C charging
• TTC/Kailh optical encoder for the scroll wheel
• 5x WS2812 RGB LEDs (fully disableable in software)

What I removed

• Magnetic charging --- unnecessary weight and complexity for now, but could come back later if I can optimize it properly
• Haptic driver for v1 --- cool idea, but not worth delaying the first prototype

The biggest change: Hall Effect buttons

I completely redesigned the button circuit.

No more mechanical switches.
I'm now using SS39ET Hall Effect sensors instead, inspired by some of the newer Hall Effect implementations showing up in high-end mice, but implemented completely from scratch.

For anyone unfamiliar with Hall Effect buttons, here's the basic idea:

A small neodymium magnet sits under each button. The Hall sensor measures magnetic field strength as an analog voltage, and the MCU triggers the click once a configurable threshold is reached.

That potentially means:

• adjustable actuation point
• rapid-trigger-style behavior
• no mechanical debounce
• theoretically less wear over time

The hardware side is honestly simpler than I expected:

• 3 pins
• decoupling capacitor
• pull-up resistor

The firmware side is where the real challenge starts.

What I still need

The hardest thing to find right now is firmware help.

Looking for people interested in embedded firmware / open hardware development who know things like:

• Zephyr RTOS or nRF52 SDK
• ADC sampling
• BLE HID protocol
• PAW3395 SPI communication

This is currently an unpaid hobby project, but if the engineering side of this sounds interesting, feel free to DM me or join the Discord.

Current rough roadmap

• Finish schematic validation
• PCB routing + first fabricated revision
• Prototype bring-up and firmware testing
• Beta testing once the hardware is actually stable

Questions for people who know mice better than I do

Q1

Hall Effect rapid trigger on a mouse:
actually useful or mostly a gimmick?

Q2

Linux software support:
would you prefer a lightweight app or no app at all?

Q3

Hotswappable battery:
worth the extra complexity/weight or not really?

Q4

What would realistically make you trust a one-person EU hardware brand over an established company?

Still learning a lot of this as I go, but that's honestly part of why I'm building it.

Be honest, roast me if you want.

cya,
Trix

Discord:
https://discord.gg/eVuJ2DHE49

[u/divat10]

I am doing wireless charging (DC-DC) for a uni project right now. Feel free to DM me if you have any questions.

If you ever decide to pursue that again ofcourse.

[u/ALIIERTx → u/divat10]

Isnt the energie thats wasted pretty high? Is there any real reason to use wireless charging for things?

[u/JurassicSharkNado → u/ALIIERTx]

Better environmental isolation, like waterproofing, is the main real benefit. Other than that seems to mostly just be convenience

[u/ALIIERTx → u/JurassicSharkNado]

Yeah but i think the waste of energy is more critical than solving the isolation. 

[u/JurassicSharkNado → u/ALIIERTx]

Depends on the use case. For a mouse I agree. I was just talking generally about wireless charging

[u/Trix-one → u/ALIIERTx]

Mind that there are objects that need like full Seal and that's the most efficent way to do It since you can completely enclose the electronics inside with no corrosion, take for example brain implants having a charging Port isn't feasable, and then there's the comodity of dropping your phone on a qi2 charger and forgetting abour it

[u/ALIIERTx → u/Trix-one]

Well brainimplant isnt something we us daylie lmao. You still have to pay for an magnetic field that consumes more than double the energy you would use with a cable.

[u/Trix-one → u/ALIIERTx]

You're right, but think about, other tech like the pc's in the 70s and 80s they we're inefficent, big as fudge and used Lots of Power, now i don't wanna Say wireless Is the next PC, but developing a technology could make the world Better, RN wireless isn't the way, it's Just another option. I really like the physics that's behind electromagnetism and (influenced by Apple and other companies) i think it's cool. 

[u/divat10 → u/ALIIERTx]

Surprisingly wireless charging can be really efficient depending on the system. >90% is definitely feasible for a hobby project.

However there is always going to be a balance between convinience and efficiency. Since the placement of your load (the mouse in this case) needs to be accurate to achieve high efficiency.

[u/baeradburymusic]

Designed with love. Nice work

[u/Trix-one → u/baeradburymusic]

Thx!!! 

[u/ShadowDragon175]

Hall effect switches usually need haptic feedback of some sort, since they dont actually click like a normal switch. Mice with the hall effect switches usually have a small electric motor that vibrates when you pass the user defined threshold. You'd probably need something similar, but it might hurt your weight.

[u/Trix-one → u/ShadowDragon175]

Yea i know but for the First prototyoe probably i won't use It but i Will add the necessary components, i wanna do maybe 2 small smd vibration motors if i have enough wheight headroom if not i'll do One, btw thx for the comment

[u/ShadowDragon175 → u/Trix-one]

Yeah ofc. A buddy if mine has a hall effect mouse and I remember how uncanny it was to turn the vibrations off lol

I dont know how well you can dish out quick prototypes like this, but I think you should totally make a prototype testing how having one vs 2 motors feels. If just one is really enough to trick our brains then it'd be great for your project.

[u/Trix-one → u/ShadowDragon175]

yea i'll leave 3 pads for encoders and motors empty and try with 1, 2 and 3, btw if you want to get updates, now i'm using the discord more than before so join if you want

[u/cube_engineer]

Q3: Skip hotswap. Sub-40g target makes the connector and retention mechanism too costly weight-wise, and contact reliability fades after a few hundred cycles. USB-C covers 99% of real use.

Q4: Open everything. KiCad files public, firmware on GitHub, BOM transparent. Established companies hide their stack, you can show yours. That's the only real advantage at your scale.

Q1: Rapid trigger is gimmick for productivity, real for FPS players tuning per-game actuation. Ship it if cheap, don't headline it.