Build Your Own MIM

Mouse Input Modifier · Open Hardware · Build it in an afternoon

MIM is open hardware — and that's the whole point. The device that reshapes your mouse input in real time is something you can hold, open up, and build yourself. No locked-down black box: the exact same firmware that ships in the finished Alpha units runs on a Teensy you solder at your own kitchen table. Start with a bare-bones board in about 25 minutes, or go all the way to a full build with dual displays and encoders in an aluminium enclosure. Three tiers, each one building on the last, and firmware flashing that works the same across all of them.

Not into soldering? You don't have to be. Ready-to-use MIM units are available on request — no iron, no wiring, just plug in and play. Say hi on Discord and we'll sort you out. The build guide below stays right here for whenever you get curious.

Build Tiers Overview

Tier	Name	Soldering	What you get
Tier 1	Bare Bones	~25 min, basic skills	Fully functional, no enclosure
Tier 2	Compact Build	~40 min	Permanently soldered, reset button, stable
Tier 3	Full Build	~2 h	2× TFT, 2× encoder, aluminium enclosure

Tier 1 — Bare Bones #

Goal: The fastest possible path to a working MIM — just a handful of solder joints. Perfect for a first taste before you commit to a fancier build.

Parts

Part	Source	Note
Teensy 4.1	SparkFun / DigiKey	SparkFun DEV-20360
Micro-USB cable	any	Teensy → PC
USB-A socket on breakout board	AliExpress / Amazon	for mouse / keyboard / controller
4× jumper wires (male–female)	any	10–15 cm is enough
Soldering iron + solder	—	Basic equipment

USB Host Pin Assignment

The Teensy 4.1 has five pads on its bottom side for the USB host connection. This is where you connect the mouse, keyboard, or controller.

Pad 2  →  +5V   (USB Pin 1)
Pad 3  →  D−    (USB Pin 2)
Pad 4  →  D+    (USB Pin 3)
Pad 5  →  GND   (USB Pin 4)
Pad 6  →  GND   (optional, can share with Pad 5)

Teensy 4.1 — USB Host pads on the bottom side

Teensy 4.1 — Bottom side with USB Host pads (Pads 2–6). Red = +5 V, White = D−, Green = D+, Black = GND.

MOUSE / KEYBOARD / CONTROLLER
        │
  USB-A Socket (Breakout)
  Pin 1 (+5V)  ──── Teensy bottom Pad 2
  Pin 2 (D−)   ──── Teensy bottom Pad 3
  Pin 3 (D+)   ──── Teensy bottom Pad 4
  Pin 4 (GND)  ──── Teensy bottom Pad 5
        │
     [Teensy 4.1]
        │
  Micro-USB (top)
        │
       PC

Bare Bones build — three connection variants

Bare Bones build — left: with deleyCON USB-A adapter and extension cable; center: with right-angle USB-A socket; right: mounted on breadboard with wiring.

Optional: Built in an Enclosure

The Bare Bones build fits into a compact aluminium enclosure — no additional soldering required, just cable management and a USB-C panel-mount adapter.

Bare Bones MIM build in aluminium enclosure

Completed Bare Bones build in aluminium enclosure with MIM label and USB-C cable.

Wiring #

For more complex builds, correct wiring according to the firmware implementation is essential. The diagram below shows the full connection overview for all supported configurations.

MIM Wiring Diagram v03 — Overview

Tier 2 — Compact Build #

Builds on Tier 1. This is the one you'll actually keep on your desk: permanently soldered on perfboard, with a proper reset button and buffer capacitors. Rock-solid even with high-resolution gaming mice (Beast X Pro, 4K polling) — set it up once and forget about it.

Additional Parts vs. Tier 1

Part	Value / Type	Source	Note
Perfboard	~80 × 50 mm	AliExpress / Conrad	Teensy fits on 56-pin board
Buffer capacitor 1	1000 µF / 16 V, Low-ESR	Conrad / Reichelt	Electrolytic, on USB host VBUS/GND
Buffer capacitor 2	100 nF, MLCC	Conrad / Reichelt	Ceramic, parallel to electrolytic
Reset button	Momentary, illuminated	AliExpress	e.g. RUNCCI-YUN 16 mm
USB host cable	USB-A socket with pigtail	AliExpress	instead of breakout board
Wire	4× 0.25 mm²	any	for USB host wiring

Why Capacitors?

High-resolution mice (2000Hz and more) can cause brief voltage drops on the VBUS line during enumeration, leading to connection drops. The capacitors buffer these spikes directly at the Teensy's host port.

Placement: both capacitors in parallel between Pad 2 (+5V) and Pad 5 (GND) on the bottom of the Teensy, as close to the pads as possible.

Tier 2 build progression — breadboard to compact enclosure

Left: Bare Bones build on breadboard. Center: Compact build with capacitors, USB-A socket, and illuminated reset button. Right: Finished build in compact enclosure.

Reset Button

The reset button provides direct access to the HalfKay bootloader — useful when the firmware has locked up or for a manual firmware update.

Connection: Program pad (top left on Teensy, labelled) → GND

[Button] ──── Program pad (Teensy front side, top left)
[Button] ──── GND

A brief press → Teensy boots into the HalfKay bootloader. Teensy Loader recognises it automatically and waits for a new firmware image.

Assembly Order

Place Teensy on perfboard, solder pin headers
Mount USB-A socket with pigtail at the edge of the perfboard
Solder capacitors to the bottom of the Teensy (watch electrolytic polarity!)
Solder USB-A cable to host pads (pin assignment as Tier 1)
Wire reset button (Program → GND)
Double-check all connections before first power-on

Tier 3 — Full Build #

Builds on Tier 2. The full experience: dual TFT displays, two encoders, an aluminium enclosure and a panel-mounted USB-C socket. Tune your curves live on the device, no laptop needed. This is exactly the Alpha Edition build — the same unit you'd get if you ordered a finished one.

Additional Parts vs. Tier 2

Part	Type	Source	Note
TFT Display 1+2	ST7789, 240×280, SPI	AliExpress	2 pieces
Encoder 1+2	KY-040 with button	AliExpress	2 pieces
Enclosure	Hammond 1455KGYBK	Mouser / RS Components	120 × 65 × 27 mm
End panels	ABS, matching Hammond 1455	Hammond / Mouser	or 3D print
USB-C Panel-Mount	CF-V8RI, 90°, 10 cm	AliExpress	Micro-B Male → USB-C Female
Screws / standoffs	M2.5, assortment	Amazon	for perfboard mounting inside enclosure

Encoder Assignment

E1 (left)   — Navigation (select parameter)
E2 (right)  — Change value / mode toggle (LongPress)

Both encoders: CLK, DT, SW pins each to free digital pins on the Teensy.

TFT Displays (SPI)

Both displays share the SPI bus (MOSI, SCLK, common) but each has its own CS and DC pin.

Display 1: CS → Pin X, DC → Pin Y
Display 2: CS → Pin A, DC → Pin B

MIM Full Build — interior view: perfboard in enclosure, TFTs and encoders installed

Full Build — interior view: perfboard mounted in enclosure slots, both TFTs installed, cable routing completed.

MIM Full Build — both TFT displays active with speed curves and encoder values

Full Build — both TFT displays active: speed curve (top) and Y-speed profile values (bottom). Left and right encoder for navigation and value adjustment.

MIM Full Build — alternate angle, both displays and encoders visible

Full Build from above — both displays and encoders visible. Device connected and in use.

Initial Firmware Flash

The same firmware runs on all three hardware tiers — no per-tier configuration needed.

Download Teensy Loader (pjrc.com) and install it
Go to mim-control.com/dev-options and download the latest MIM Firmware A .hex file
Open the .hex in Teensy Loader, connect the Teensy via Micro-USB, press the white button on the Teensy — it flashes automatically

Teensy Loader with loaded .hex file, progress bar during flash

Teensy Loader with the MIM firmware .hex loaded — progress bar during flash.

Test the Connection

Open a browser (Chrome or Edge — Firefox does not work)
Go to mim-control.com
Click Connect — device should appear
Connect mouse — MIM tab becomes active

mim-control.com — connection flow: port selection to fully connected

mim-control.com — left: port selection dialog; center: correct port selected; right: connected with full MIM interface, speed curves, and serial monitor active.

Firmware Update

After the initial flash, updates can be installed directly from the browser.

Go to mim-control.com/update
Current vs. available version is shown
"Download firmware" → .hex file is loaded
Press the white button on the Teensy briefly → boots into bootloader
Teensy Loader detects the bootloader and flashes automatically

Tier 2 and Tier 3 have a dedicated reset button — use it instead of the white button on the Teensy board.

AIM / CIM — XInput Mode

AIM converts mouse input into joystick deflection (XInput output). CIM passes a connected controller through with correction applied. Both modes output XInput signals instead of standard HID.

These modes require Firmware C — a separate firmware image available on mim-control.com/dev-options under "Firmware C". Flash it the same way as Firmware A using Teensy Loader.

Note: mim-control.com does not work with Firmware C. Configuration requires external tools. To return to MIM / KIM, simply flash Firmware A again.

Help & Community

Questions, problems, preset sharing — all in the Discord:

→ Join Discord

And if you'd rather skip the build entirely: ask about a ready-to-use unit there too — same place, same friendly people.

Video build guide:

→ Watch on YouTube

MIM · Mouse Input Modifier · github.com/boa-constrictor-42 · DIY Guide v1.0