Custom ESP32-S3 board for simracing

February 24, 2026 ยท View on GitHub

Custom DevKit

Note

This board has been manufactured and tested (REV2). It works.

Features

  • ESP32-S3.

  • 4MB flash and 2MB PS-RAM.

  • External power supply (~5V DC) via quick release or cable.

  • Optional LiPo/Li-ion battery.

  • Battery charger:

    • Supports safe battery charging and discharging simultaneously. This also enhances battery life.
    • Automatically switches from external power to battery.
    • The charging current is automatically adapted to the state of charge with priority to the ESP32. The maximum charging current is 300 mA.
    • LiPo and Li-ion chemistries.

  • "Fuel gauge" (state of charge).

  • BLE (wireless) or USB (wired) connectivity.

  • 32 switches.

  • 8 rotary encoders. Can also be configured for other uses.

  • 2 analog clutch paddles (potentiometers or HE sensors).

  • 2 RGB LED strips (user-selected power).

  • 10 additional GPIO pins available for customization. Can be expended in additional switches, rotary encoders, etc.

  • 50.8mm and 70mm quick release mounting holes. Special care must be taken not to crush the PCB with the fastening screws of the quick release. Use additional nuts to prevent this.

Antenna

An external antenna is required (you have to purchase one separately). The following coaxial connectors are compatible:

  • W.FL Series connector from Hirose.
  • MHF III connector from I-PEX (also known as IPEX3)
  • AMC connector from Amphenol

Note that U.FL connectors are not compatible.

It is recommended to select an antenna that meets the following requirements:

  • 2.4 GHz band.
  • 50 ohm impedance.
  • The maximum gain should not exceed 2.33 dBi.

You can find them in the Adafruit store, AliExpress or other retailers.

Power supply

There are three power plugs in the board:

  • 5V and GND pads (for short, "external power").

    Take care not to swap those terminals. There is no reverse polarity protection. Connect this plug to the quick release if available or to a power connector housed in the casing. If you have a Simagic QR, GND is the yellow wire and 5V is the green one. Labeled as External power in the board.

  • USB cable.

    Under no circumstances should you connect both power plugs simultaneously. You could damage the board or your simracing gear. Detach the external power plug before connecting the USB cable. Keep this present when uploading firmware.

  • Battery + and - pads ("Battery plug" for short). There is reverse polarity protection in the battery charger, but not in the fuel gauge. Take care not to swap those terminals.

Power requirements

  • External power plug:

    • DC voltage: min. 4V6, max. 10V. There is over voltage protection.
    • Input current: max. 1A.

  • Battery (optional):

    • Just one battery is supported. Do not attach two or more batteries, not in parallel, nor in series.
    • Only LiPo or Li-ion chemistries are supported.
    • Single-cell "1S" battery, max. 4V7.

Support for LED strips

Two optional single-wire LED strips are available. You must choose a power supply for the LED strips (labeled VLED) using the onboard switch:

  • 5V:

    VLED is connected directly to the external power plug. In such a case, the power supply must meet the requirements of the LED strips, which are typically a maximum of 5.3 volts DC. This option provides unregulated power, but sufficient voltage. It will not work without a permanent external power supply.

  • 3V3

    VLED is connected to the 3V3 LDO regulator, providing constant voltage and brightness. However, the voltage may not be sufficient to display the correct colors. You can reduce the global brightness to compensate for this. This option works if power is supplied either from the battery or from an external source.

  • VBAT

    If the external power supply is connected, this option provides constant brightness at 4.4 regulated volts (sufficient for any LED strip). If not, this option powers the LED strips directly from the battery. The colors will be correct but will fade as the battery runs out. Power may fluctuate while the battery is charging.

Please, operate the VLED switch while there is no power supply.

External wiring

Use GND as a common pole for all switches and rotary encoders. There are more than enough GND pads available on the board. However, you can also chain GND from one switch (or rotary encoder) to the next.

There are two 3V3 pads available to power other devices, but note that the maximum current the board can deliver is 1A to the whole system.

The Charging pad works in open-drain mode and is active LOW. You can attach a LED witness via a 1K-ohm resistor in this way:

flowchart LR
  charging(charging pin)
  resistor[1K resistor]
  led("(cathode)-|<--(anode)")
  power(3V3)
  charging --- resistor --- led --- power

The pin out is printed on the back of the board:

Pin out

System shutdown

It is recommended to attach a non-momentary switch to one pole of the battery to shutdown the system. The firmware is also able to enter deep sleep mode as a shutdown option. It will deplete the battery but at a very slow rate. To wake up the system you can configure one of the RTC pins (assigned to the rotary encoders) or attach an external push button to the Reset pads.

GPIO configuration

  • RGB LED strips:

    GPIO 40 (Din1) and GPIO 38 (Din2) must be configured in open drain mode, as those pins are pulled up.

  • Primary I2C bus

    GPIO 8 (SDA) and GPIO 9 (SCL) must be configured as the primary I2C bus. The I2C bus has external pullup resistors. Two GPIO expanders are attached to this bus. Their hardware addresses are 0 and 7 (decimal).

  • Rotary encoders:

    Rotary #A pinB pin
    1GPIO 4GPIO 5
    2GPIO 7GPIO 6
    3GPIO 11GPIO 10
    4GPIO 13GPIO 12
    5GPIO 17GPIO 18
    6GPIO 16GPIO 21
    7GPIO 15GPIO 33
    8GPIO 14GPIO 34

    Note that A and B pins can be customized for other uses, for example, additional switches.

  • Analog clutch potentiometers (ADC pins)

    • Right clutch paddle: GPIO 1 (potentiometer 1)
    • Left clutch paddle: GPIO 2 (potentiometer 2)

  • Other GPIO pins available for customization:

    35, 36, 37, 39, 41, 42, 47, 48, RXD0 and TXD0.

  • GPIO pins not available:

    • GPIO 3 (bootstrap)
    • GPIO 26 (PSRAM)
    • GPIO 45 (bootstrap)
    • GPIO 46 (bootstrap)

Manufacturing

Link to project in Open Source Hardware Labs: https://oshwlab.com/afpineda/simwheelkit_esp32_unified. You can one-click order manufacturing from that site.

Take this information into account when ordering:

  • This board is designed for the JLC04161H-3313 physical stacking.
  • Minimum hole (via) size is 0.3mm (12mil).
  • PCB thickness is 1.6mm.
  • Copper weight:
    • Outer: 1oz
    • Inner: 0.5oz
  • You can safely choose the cheapest via covering.
  • 4 layers (Signal/power + GND + GND + Signal/power).
  • Pin headers are not included in the bill of materials (BOM) on purpose. You can safely ignore any error message regarding them. Direct wire soldering is a better option than pin headers for the intended application, but you can choose to mount them: open in EasyEDA PRO, select each pin header and change the property Add into BOM to true.
  • If you choose to include the pin headers in the BOM, take into account that PWRH1 is mounted on the back, as this is the place where the quick release have the wires.
  • Each quick release may require a different connector.

Files

Firmware customization

Arduino's sketch named CustomDevKitFirmware is the place where you build your own firmware by modifying a few specific lines of code. You may want to make a copy first to prevent your customized code from being deleted after updating. To make a working copy:

  • Copy the entire folder under a different name. Place that copy in the src/Firmware folder.
  • Make sure that both the folder and the ".ino" file inside it have exactly the same name.

There a few things to customize as noted in the sketch file:

  • To configure a custom device name and manufacturer modify the following lines:

    std::string DEVICE_NAME = "Custom steering wheel";
std::string DEVICE_MANUFACTURER = "Me";

  • If you have BLE connectivity and battery power without a power on/off switch, modify SHUTDOWN_ON_DISCONNECTION in this way:

    #define SHUTDOWN_ON_DISCONNECTION true

    Additionally, configure a wake up pin in this line:

    #define WAKE_UP_PIN ROT1A

    which is configured to the first rotary encoder by default. For rotary encoders, you can use either the A or B pins.

    You can also wire an external push button to the Reset pads for wake up.

  • If you have USB connectivity, or you have BLE connectivity with external power, or you have BLE connectivity with battery power and a power on/off switch, leave SHUTDOWN_ON_DISCONNECTION in this way:

    #define SHUTDOWN_ON_DISCONNECTION false

  • Configure the LED strips by setting the number of pixels on each. If you are not using an LED strip, set it to zero.

    #define LED_STRIP1_COUNT 8
#define LED_STRIP2_COUNT 0

    By default WS2812 pixel drivers are configured, but you can change that.

  • If you don't have battery power, modify ENABLE_BATTERY in this way:

    #define ENABLE_BATTERY false

  • If you have battery power, leave ENABLE_BATTERY unmodified:

    #define ENABLE_BATTERY true

    and choose whether you want the system to shutdown on very low battery levels:

    #define SHUTDOWN_ON_LOW_BATTERY false

    write false or true to the right of SHUTDOWN_ON_LOW_BATTERY.

You can further customize the firmware at will. See the customization how-to.

Firmware uploading

No PC driver needs to be installed. Your board must enter bootloader mode for the serial port to become available and Arduino IDE recognizing the board. To enter bootloader mode, press and hold BOOT, then press and release RESET, then release BOOT.

In Arduino IDE, configure your board in this way ("Tools" menu):

  • Board: ESP32S3 Dev Module (esp32).
  • USB-Mode: "USB-OTG".
  • USB CDC on Boot: "Disabled".
  • Upload mode: USB-OTG CDC (TinyUSB).

Important

You must click on the Reset button after uploading.

Arduino IDE settings for troubleshooting

The previous Arduino IDE options do not enable the USB serial output for troubleshooting in the serial monitor. If you need the serial monitor, use the following options:

  • Board: ESP32S3 Dev Module (esp32).
  • USB-Mode: "USB-OTG".
  • USB CDC on Boot: "Enabled".
  • Upload mode: USB-OTG CDC (TinyUSB).

But USB HID connectivity will be disabled in this case (there is BLE connectivity only).

Hardware revisions

  • REV 2: First publicly available PCB.

  • REV 1: Not publicly available.