Button Box Get in touch

In development · Hardware and firmware

Button Box

A sim-racing button box with its own circuit board and enclosure. No hot glue involved.

Get in touch See it working

BT1–BT6 · press a button, follow the schematic

Schematic for one button: the switch input to the STM32 and the LED driver from the 74HC595 INPUT +3V3 BT1 R3310 Ω R13.3 kΩ C310 nF BUTTON1 U1 STM32L432PA0 · pad 6 0 LED VBUS BT1 LED R1927 Ω Q12N7002 R1710 kΩ R15100 kΩ U4 74HC595QA · pad 15

U1 reads, active high

  1. 0PA0
  2. 0PA8
  3. 0PA9
  4. 0PA10
  5. 0PA15
  6. 0PB0

SPI byte into U4, latched by SR_CS

  1. 0QH
  2. 0QG
  3. 0QF
  4. 0QE
  5. 0QD
  6. 0QC
  7. 0QB
  8. 0QA
From the production schematic, with the buttons on their 30 mm grid as on the board. Holding a button lights its LED here so you can see both paths. That part’s only an illustration, since there’s no firmware in this repository.
Title
Button Box
Dwg no.
Q2-001
Rev
2026.1
Status
In development
Drawn by
DWMM Holdings

Notes

What it does.

The electrical and mechanical design for the Mission City Motorsport button box: schematic, board layout and enclosure, built around an STM32L432. There’s also a battery board for a wireless version (schematic only) and an enclosure for a matching volume box.

  1. 01

    KiCad schematic and PCB layout, with a matching enclosure design

  2. 02

    Uses the shared in-house symbol and footprint libraries

The board

What’s on it.

One STM32L432KC handles everything: six inputs, an SPI bus shared by the LED shift register and an EEPROM, and USB.

RefPartJob
U1STM32L432KCReads the six buttons and drives the shift register and EEPROM over SPI.
U474HC595Shift register for the six button LEDs, each switched by a 2N7002.
U225LC SPI EEPROMShares the SPI bus, with its own chip select.
U3AP2112K-3.3The 3.3 V regulator, fed from USB.
J3, J6USB-CPower and data, with TPD2E009 ESD protection.
J4Tag-Connect TC2030SWD for programming and debug.
BT1–BT6RP8100Push buttons with built-in LEDs.

Where it stands

The electronics are drawn. Parts are next.

  1. 01

    Electrical design

    Done. The schematic is drawn and the 69 × 86 mm board is laid out in KiCad, using the shared in-house symbol and footprint library.

  2. 02

    Parts

    Sourcing the bill of materials is still open.

  3. 03

    Enclosure

    Designed in SolidWorks: a box body, faceplate and rig mount for 3D printing, plus a matching volume box.

  4. 04

    Wireless version

    A 1S2P battery board, drawn as a schematic only.

Specification

What it’s built with, and when.

Pulled from the repository each time this site is built.

State
In development
Discipline
Hardware systems
Shape
Hardware and firmware
Started
Aug 2026
Last change
Aug 2026
Commits
13
  • KiCad
  • STM32L432
  • SolidWorks
  • Python 100%

Related work

Built alongside Button Box

KiCad Libraries A shared KiCad library for in-house parts Mission City Motorsport The website, stream overlay and shared components for a sim-racing team STM32 Platform A firmware platform for STM32 with no vendor code in the build

Next

Build on Button Box

Ask about licensing the platform, bringing up a board, or contract firmware work.

Email dmoore@dwmmholdings.com How it works

This site isn't finished. Anything on it may still change, and none of it is binding until the site is live.