Kart Medulla (ESP32)
The Kart Medulla is the ESP32-based control hub that interfaces between the Orin computer, sensors, and actuators. The standard board is the ESP32-DevKitC V4 (38-pin, USB-C) with an ESP32-WROOM-32D module; the older 30-pin board is legacy-only. The system is moving to a dedicated interface PCB that consolidates level shifting, analog conditioning, and IO breakout.
Firmware repository: UM-Driverless/kart_medulla
ESP32 Overview
- CPU: Xtensa dual-core (or single-core) 32-bit LX6 microprocessor
- Clock Speed: Up to 240 MHz
- Wi-Fi: 802.11 b/g/n
- Bluetooth: Bluetooth v4.2 BR/EDR and BLE
- Flash Memory: Up to 16 MB
- SRAM: 520 KB
- GPIOs: 34
- ADCs: 18-channel, 12-bit
- DACs: 2-channel, 8-bit
- Communication Interfaces: SPI, I2C, UART, CAN, I2S
ESP32 Standardization Decision
The project previously used a 30-pin ESP32 development board with a non-standard pinout that is not DevKitC-compatible. To ensure long-term repeatability, predictable wiring, and easy replacement across builds, the project now standardizes on the ESP32-DevKitC V4 (38-pin, USB-C) using the ESP32-WROOM-32D module with an integrated PCB antenna. DevKitC V4 is Espressif's reference design with a stable pinout, reliable auto-reset/boot circuitry, and wide toolchain support. The ESP32 core is identical across boards; the change is driven by hardware consistency and robustness, not performance. The 30-pin board remains deprecated and should not be used for new builds.
ESP32-DevKitC Dimensions
Current ESP32-DevKitC V4 Configuration
The ESP32-DevKitC V4 (with ESP32-WROOM-32D module) serves as the medulla of the kart, interfacing between the Orin computer, steering angle sensor, and motor controllers.
Pin Assignments
Motor Control Outputs
| GPIO Pin | Function | Type | Range | Description |
|---|---|---|---|---|
| GPIO 26 | Throttle | DAC2 | 0-255 | Analog throttle control |
| GPIO 25 | Brake | DAC1 | 0-255 | Analog brake control |
| GPIO 27 | Steering PWM | LEDC | 0-255 | Steering motor PWM |
| GPIO 14 | Steering DIR | Digital | 0/1 | Steering motor direction |
Sensor Interface (AS5600)
| GPIO Pin | Function | Connected To | Description |
|---|---|---|---|
| GPIO 22 | I2C SCL | AS5600 SCL | Clock signal |
| GPIO 21 | I2C SDA | AS5600 SDA | Data signal |
AS5600 Status
The AS5600 magnetic angle sensor remains disabled in firmware until hardware is physically connected.
Auxiliary Pins
| GPIO Pin | Function | Connected To | Description |
|---|---|---|---|
| GPIO 2 | Status LED | Onboard LED | Status indicator |
| GPIO 18 | UART TX | Orin RX | Serial communication to Orin |
| GPIO 19 | UART RX | Orin TX | Serial communication from Orin |
Wiring Connections
ESP32 to AS5600 Angle Sensor
| AS5600 Pin | ESP32 Pin | Wire Color (2025) |
|---|---|---|
| SCL | GPIO 22 | Blue |
| SDA | GPIO 21 | Green |
| VCC | 3.3V | White |
| GND | GND | Grey |
Temporary Color Code
Wire colors are specific to the 2025 version and not official. Always verify connections.
ESP32 to Motor Controllers
Throttle Control
| Motor Driver Pin | ESP32 Pin | Signal Type |
|---|---|---|
| Analog Input | GPIO 26 | DAC2 (0-255) |
| VCC | 5V | Power |
| GND | GND | Ground |
Brake Control
| Motor Driver Pin | ESP32 Pin | Signal Type |
|---|---|---|
| Analog Input | GPIO 25 | DAC1 (0-255) |
| VCC | 5V | Power |
| GND | GND | Ground |
Steering Control
| Steering Driver Pin | ESP32 Pin | Signal Type |
|---|---|---|
| PWM | GPIO 27 | LEDC (0-255) |
| DIR | GPIO 14 | Digital (0/1) |
| VCC | 5V | Power |
| GND | GND | Ground |
ESP32 to Orin (UART Communication)
| Orin Pin | ESP32 Pin | Direction |
|---|---|---|
| RX | GPIO 18 | ESP32 -> Orin |
| TX | GPIO 19 | Orin -> ESP32 |
| GND | GND | Ground |
UART Configuration
Serial communication enables future integration between the Orin computer and ESP32 for command/telemetry exchange.
Kart Medulla Interface PCB (In Progress)
The interface PCB (a.k.a. esp32_expander in the repo) hosts the electrical conditioning and connectors so the ESP32 module can be swapped while keeping wiring consistent.
Draft Hardware Decisions
- Shutdown: use a MOSFET (N-channel low-side or P-channel high-side).
- Analog outputs: use ESP32 DACs with a dual op-amp for gain (x1.5 to 5V throttle, x3 to ~9.99V Festo pressure sensor).
Connector Pinout (Outside World)
The main connector is a set of green push-in headers labeled CN1..CN4 in the schematic.
| Connector | Pin | Signal | Notes |
|---|---|---|---|
| CN1 | 1 | HALL3_5V | |
| CN1 | 2 | HALL2_5V | |
| CN1 | 3 | HALL1_5V | |
| CN2 | 1 | PRESSURE1_0V10 | |
| CN2 | 2 | PRESSURE2_0V10 | |
| CN2 | 3 | PRESSURE3_0V10 | |
| CN3 | 1 | GND | |
| CN3 | 2 | STEER_CMD_DIR_3.3V | |
| CN3 | 3 | STEER_CMD_PWM_3.3V | |
| CN4 | 1 | 3.3V | |
| CN4 | 2 | STEER_SDA | |
| CN4 | 3 | STEER_SCL |
ESP32 Header Pinout (Software Names)
Mapping between the ESP32 38-pin numbering and the DevKitC V4 Type-C headers (H1/H2). ESP32 pins 1-19 correspond to H2 pins 1-19, and ESP32 pins 20-38 correspond to H1 pins 1-19. Pin numbers match the header labels in the diagram.
| ESP32 Pin | H1 Pin | H2 Pin | Signal |
|---|---|---|---|
| 1 | - | 1 | 3V3 |
| 2 | - | 2 | EN |
| 3 | - | 3 | PRESSURE_1_0_3V3 |
| 4 | - | 4 | PRESSURE_2_0_3V3 |
| 5 | - | 5 | PRESSURE_3_0_3V3 |
| 6 | - | 6 | PEDAL_ACC_3V3 |
| 7 | - | 7 | PEDAL_BRAKE_3V3 |
| 8 | - | 8 | MOTOR_HALL_2_3V3 |
| 9 | - | 9 | CMD_ACC_0_3V3 |
| 10 | - | 10 | CMD_BRAKE_0_3V3 |
| 11 | - | 11 | HYDRAULIC_1_0_3V3 |
| 12 | - | 12 | HYDRAULIC_2_0_3V3 |
| 13 | - | 13 | NC (STRAP pin - flash/boot config risk) |
| 14 | - | 14 | GND |
| 15 | - | 15 | SDC_NOT_EMERGENCY_3V3 |
| 16 | - | 16 | RESERVED (FLASH/SDIO) |
| 17 | - | 17 | RESERVED (FLASH/SDIO) |
| 18 | - | 18 | RESERVED (FLASH/SDIO) |
| 19 | - | 19 | 5V |
| 20 | 1 | - | RESERVED (FLASH/SDIO) |
| 21 | 2 | - | RESERVED (FLASH/SDIO) |
| 22 | 3 | - | RESERVED (FLASH/SDIO) |
| 23 | 4 | - | NC (STRAP pin - boot config risk) |
| 24 | 5 | - | NC (STRAP pin - boot config risk) |
| 25 | 6 | - | NC (STRAP pin - BOOT mode pin) |
| 26 | 7 | - | NC (STRAP pin - boot config risk) |
| 27 | 8 | - | MOTOR_HALL_3_3V3 |
| 28 | 9 | - | MOTOR_HALL_1_3V3 |
| 29 | 10 | - | NC (STRAP pin - boot config risk) |
| 30 | 11 | - | CMD_STEER_PWM_3V3 |
| 31 | 12 | - | CMD_STEER_DIR_3V3 |
| 32 | 13 | - | GND |
| 33 | 14 | - | STEER_SDA_I2C |
| 34 | 15 | - | RESERVED (USB UART0 RX) |
| 35 | 16 | - | RESERVED (USB UART0 TX) |
| 36 | 17 | - | STEER_SCL_I2C |
| 37 | 18 | - | SPARE_3V3 |
| 38 | 19 | - | GND |