Multi-Functional Controller (MFC) & 4WD RC Vehicle

1. Project Overview & Aim

• Primary Goal: Engineer a high-performance, bare-metal handheld remote controller (MFC) from scratch using an ESP32-S3-N16R8, paired with a custom 4WD RC Vehicle controlled by an ARM Cortex-M3 (GD32F103C8T6).
• Secondary Objectives: Extend the controller's capabilities to include a cloud-connected AI voice assistant (MAX4466), local FAT32 SD card telemetry logging, and PC Gamepad (USB HID / Bluetooth) support.
• Tech Stack: C/C++, ESP-IDF v5.x (FreeRTOS), bare-metal register manipulation, SPI, I2C, Hardware Pulse Counter (PCNT), and One-Shot ADC1.

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2. Current Situation & Hardware Prototype

• Controller Prototype: Currently prototyped on a 6×9 cm perfboard. The ESP32-S3-N16R8 communicates over a shared SPI2_HOST bus with a Nordic nRF24L01+ 2.4 GHz transceiver and a temporary 1.3" SH1106 OLED display, decoupled by a 100 µF electrolytic capacitor across the radio rails.
• Firmware: A deterministic FreeRTOS state machine (firmware/main/mmcontroller.c) handles hardware quadrature decoding (PCNT) for a KY-040 rotary encoder menu UI, 300 ms software button debouncing, ADC1 joystick polling, and live 2.4 GHz RF channel configuration (0–125).
• Display Hardware Pivot (1.3" OLED \rightarrow 1.8" ST7789 TFT): Bench testing revealed that the 7-pin 1.3" OLED module lacks a physical Chip Select (CS) pin, causing SPI bus collisions when sharing the bus. We are upgrading to a 1.8" ST7789 Color TFT LCD (which exposes a dedicated hardware CS pin on GPIO 10) to share the SPI bus safely without bus contention.
• Manufacturing & Enclosure Status: Paused cutting the rigid ABS plastic project box (DT-100, 190 × 137 × 59 mm) until next month when a variable 3-speed rotary tool (Dremel/E108) and 2.35 mm diamond cutting wheels arrive to ensure clean, professional cutouts without melting the ABS plastic.

Figure 1: 6×9 cm Perfboard Controller Prototype (Top View) — ESP32-S3-N16R8 module, nRF24L01+ 2.4 GHz transceiver, 100 µF burst-smoothing capacitor, peripheral male header bus, and power rail headers.

Figure 2: Side Profile — External 2.4 GHz SMA dipole antenna connected to the nRF24L01+ transceiver and dual USB-C ports (Native USB-OTG & UART).

Figure 3: Underbody Bus Routing — Point-to-point solder bridges, common ground/power rails, and shared SPI2 signal routing on the 6×9 cm perfboard.

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3. Hardware Architecture & Bill of Materials (BOM)

3.1 Handheld Controller (MFC — Transmitter Node)

Subsystem	Component	Technical Details & Role
MCU	Espressif ESP32-S3-N16R8	Dual-core Xtensa® LX7 @ 240 MHz, 16 MB Quad SPI Flash, 8 MB Octal PSRAM.
RF Telemetry	Nordic nRF24L01+ Module	2.4 GHz ISM band transceiver over shared SPI2_HOST.
Display	1.8" ST7789 TFT Color LCD	3.3V logic, full-color SPI display with dedicated CS pin (replacing 7-pin CS-less 1.3" OLED).
Joysticks	2× K-Silver (KS) PS5 Hall-Effect Modules	3.3V active magnetic contactless gimbals for zero stick drift.
UI Input	KY-040 Rotary Encoder	Quadrature encoder (CLK, DT, SW) decoded in hardware via ESP32-S3 PCNT.
Voice AI	MAX4466 Electret Microphone Module	Analog pre-amplifier with adjustable gain for cloud-connected AI voice assistant input.
Data Logging	Arduino Micro SD Card Module	SPI interface, formatted FAT32 for local telemetry and configuration logging.
Audio Output	1× Passive Buzzer + 2× Active Buzzers	Passive buzzer for melodies + 2× active buzzers for percussive UI clicks, driven by 2N2222 NPN Transistors.
Power System	Dual 18650 Li-ion + TP4056 + MT3608	Dual 18650 cells, TP4056 charger, MT3608 DC-DC boost converter (5V rail), 100 µF electrolytic capacitor (nRF24 burst smoothing), and 100 nF ceramic decoupling caps.

3.2 RC Vehicle (Receiver Node)

Subsystem	Component	Technical Details & Role
MCU	GD32F103C8T6 Mini Board	32-bit ARM® Cortex®-M3 real-time vehicle controller.
RF Telemetry	nRF24L01+ PA+LNA Module	High-power 2.4 GHz transceiver with Power Amplifier, Low-Noise Amplifier, and external SMA antenna (~1 km range).
IMU / Navigation	MPU9250 9-DOF Sensor	3-axis Gyroscope, 3-axis Accelerometer, and 3-axis Magnetometer (I2C) for tilt-compensated heading.
Drivetrain	4× JGB37-520 12V 333 RPM Gear Motors	High-torque 12V DC gear motors with built-in quadrature encoders for closed-loop PID velocity control.
Chassis / Box	DT-100 Project Box	Rigid black ABS enclosure (190 × 137 × 59 mm).
Power System	12V Battery + Motor Drivers	12V traction battery pack, heavy-duty H-bridge motor drivers, and 12–24V Waterproof Main Switch.

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4. Pinout Definitions (ESP32-S3 Controller)

The controller firmware (firmware/main/mmcontroller.c) and schematic (hardware/mfc-1.kicad_sch) allocate pins on the ESP32-S3-N16R8 as follows:

Bus / Peripheral	Signal	ESP32-S3 Pin	Interface / Mode	Notes
SPI Hub (SPI2_HOST)	MOSI	GPIO 11	SPI Master Output	Shared data line (nRF24L01+, Display SDA, MicroSD)
SPI Hub (SPI2_HOST)	MISO	GPIO 13	SPI Master Input	Shared data input (nRF24L01+, MicroSD)
SPI Hub (SPI2_HOST)	SCK	GPIO 12	SPI Master Clock	Shared clock line (nRF24L01+, Display CLK, MicroSD)
nRF24L01+ Radio	CSN	GPIO 14	SPI Chip Select	Dedicated radio bus enable
nRF24L01+ Radio	CE	GPIO 21	Digital Output	Radio TX/RX power state activation
TFT Display (1.8" ST7789)	CS	GPIO 10	SPI Chip Select	Dedicated display bus enable
TFT Display (1.8" ST7789)	DC	GPIO 9	Digital Output	Command vs. frame data selection
TFT Display (1.8" ST7789)	RES	GPIO 8	Digital Output	Hardware display reset (BLK tied to 3.3V)
KY-040 Rotary Encoder	CLK	GPIO 15	Hardware PCNT	Quadrature channel A (1000 ns glitch filter)
KY-040 Rotary Encoder	DT	GPIO 16	Hardware PCNT	Quadrature channel B (direction sensing)
KY-040 Rotary Encoder	SW	GPIO 17	Input (PULLUP)	Push-button switch (300 ms software debounce)
K-Silver Hall Joystick 1	VRx	GPIO 4	ADC1_CH3 (12 dB)	Analog X-axis (0–3.3V active Hall sensor)
K-Silver Hall Joystick 1	VRy	GPIO 5	ADC1_CH4 (12 dB)	Analog Y-axis (0–3.3V active Hall sensor; 2nd joystick pending)

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5. Hardware Safety & Engineering Rules

1. Enclosure Machining RPM Rule: Do NOT use standard fixed 16,000 RPM rotary tools on the DT-100 ABS plastic enclosure; high friction melts ABS instead of cutting it. Machining is paused until the variable 3-speed rotary tool with 2.35 mm diamond cutting discs arrives.
2. Hall-Effect Gimbal Polarity Protection: Do NOT wire the K-Silver (KS) PS5 Hall-effect joystick VCC backward. Unlike passive potentiometers, these are active 3.3V CMOS magnetic sensors and will burn out immediately under reverse polarity.
3. 5V Sensor Level Shifting on GD32: Do NOT wire a 5V HC-SR04 ultrasonic ECHO pin directly to the 3.3V GD32F103C8T6 without a resistor voltage divider (or use the 3.3V VL53L0X I2C Time-of-Flight sensor instead).
4. nRF24L01+ Burst Decoupling: Always keep the 100 µF electrolytic capacitor across the nRF24L01+ VCC/GND pins to prevent 3.3V rail brown-outs during PTX transmission bursts.

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6. Immediate Next Steps & Engineering Roadmap

1. 1.8" ST7789 TFT Migration: Rewrite the display initialization and frame buffer logic using ESP-IDF's esp_lcd component to replace the custom 5×8 monochrome OLED driver.
2. MicroSD Card SPI & FATFS Setup: Configure the Arduino MicroSD card module on the SPI bus and initialize the FATFS virtual filesystem (VFS) for reading/writing telemetry logs.
3. NVS Hall-Effect Joystick Calibration: Write the calibration routine for the K-Silver PS5 Hall-effect joysticks—measuring resting center, minimum, and maximum voltages and saving them persistently to ESP32-S3 Non-Volatile Storage (NVS) flash.
4. GD32F103C8T6 Vehicle Receiver Firmware: Structure the ARM Cortex-M3 C codebase to poll the nRF24L01+ PA+LNA module, read MPU9250 9-DOF I2C telemetry, and run closed-loop PID motor control on the 4× JGB37-520 encoder motors.

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7. Repository Structure & Build Instructions

multi-functional-controller/
├── docs/
│   └── PROJECT_HANDOFF.md           # Canonical engineering handoff & specification
├── firmware/                        # ESP-IDF v5.x C99 Firmware Project (ESP32-S3)
│   ├── CMakeLists.txt               # Top-level CMake project configuration
│   ├── sdkconfig                    # Verified ESP32-S3 target configuration
│   └── main/
│       ├── CMakeLists.txt           # Component registration
│       └── mmcontroller.c           # Master firmware: Shared SPI2, PCNT menu UI, nRF24 tuning
├── hardware/                        # KiCad 10 Electronic Design Automation (EDA)
│   ├── mfc-1.kicad_pro              # KiCad project file
│   ├── mfc-1.kicad_sch              # Controller schematic design (ESP32-S3, nRF24L01+, 100uF cap)
│   └── mfc-1.kicad_pcb              # Board layout & routing rules
├── images/                          # High-resolution 6x9cm perfboard prototype photography
│   ├── TOP_VIEW.png                 # Front carrier board overview
│   ├── SIDE_VIEW_WITH_ANTENNA.png   # RF antenna and profile perspective
│   └── BOTTOM_VIEW.png              # Perfboard underside solder bus wiring
├── .gitignore                       # Clean repository filter (builds, caches, local configs)
├── LICENSE                          # MIT License
└── README.md                        # Master engineering documentation

Build & Flash (ESP32-S3 Controller)

. $HOME/esp/esp-idf/export.sh
cd firmware
idf.py set-target esp32s3
idf.py build
idf.py -p /dev/ttyACM0 flash monitor

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Author & Project Links

• Author: Ertunç Özbay
• Personal Workshop & Portfolio: ertuncozbay.dev
• Project Detail Page: ertuncozbay.dev/projects/multi-functional-controller.html
• License: MIT License