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 & Early Prototype Showcase (Rev 0.1)

Note

Early Prototype Notice (Rev 0.1 Carrier Build):
The photographs and schematic below represent the very early initial stage of the physical hardware build. At this stage, only the core carrier foundation is soldered onto the 6×9 cm perfboard: the ESP32-S3-N16R8 microcontroller, nRF24L01+ 2.4 GHz radio module, 100 µF electrolytic burst-smoothing capacitor, signal male pin headers, and power rail male headers.
The repository's firmware (firmware/main/mmcontroller.c) and schematic (hardware/mfc-1.kicad_sch) are intentionally kept matched to this verified Rev 0.1 hardware baseline. As the new modules (1.8" ST7789 TFT, K-Silver PS5 Hall-Effect Joysticks, MicroSD, MAX4466, 2N2222 buzzer stage, and enclosure) are physically integrated, both the hardware photos and firmware will be updated step-by-step.

• Controller Prototype (Rev 0.1): 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 benchtop 1.3" SH1106 OLED display connected via the male breakout headers.
• Current Baseline 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, 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 (hard-tied to GND internally), 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 (Early Build — Rev 0.1): Initial 6×9 cm perfboard carrier top view — ESP32-S3-N16R8 module, nRF24L01+ 2.4 GHz transceiver, 100 µF decoupling capacitor, peripheral male pin headers, and power rail male headers. (Will be updated as Phase 2 modules are installed).

Figure 2 (Early Build — Rev 0.1): Side profile showing the external 2.4 GHz SMA dipole antenna connected to the nRF24L01+ transceiver and dual USB-C ports (Native USB-OTG & UART).

Figure 3 (Early Build — Rev 0.1): Underbody point-to-point solder bridges, common ground/power rails, and shared SPI2 signal routing on the 6×9 cm perfboard.

Rev 0.1 Core Carrier Schematic (hardware/mfc-1.kicad_sch)

Figure 4: KiCad 10 schematic of the Rev 0.1 Core Carrier (`U1: ESP32-S3`, `U2: nRF24L01+`, `C1: 100 µF` decoupling capacitor).

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3. Dual-Node System Architecture & Bill of Materials (BOM)

flowchart LR
    subgraph TX["Node 1: Handheld Controller (ESP32-S3-N16R8)"]
        MCU["ESP32-S3-N16R8<br/>(FreeRTOS Dual-Core)"]
        HALL["2x K-Silver PS5<br/>Hall-Effect Joysticks"] -->|ADC1| MCU
        MIC["MAX4466 Electret<br/>Mic Pre-Amp"] -->|ADC1| MCU
        ENC["KY-040 Rotary Encoder"] -->|Hardware PCNT| MCU
        MCU -->|SPI2_HOST + CS GPIO10| TFT["1.8&quot; ST7789 Color TFT"]
        MCU -->|SPI2_HOST + CS| SD["MicroSD Card (FAT32)"]
        MCU -->|2N2222 NPN Drivers| BUZ["1x Passive + 2x Active Buzzers"]
        MCU -->|SPI2_HOST + CSN GPIO14| NRF_TX["nRF24L01+ 2.4GHz TX"]
    end

    subgraph RX["Node 2: 4WD RC Vehicle (GD32F103C8T6)"]
        NRF_RX["nRF24L01+ PA+LNA<br/>(1km SMA Antenna)"] -->|SPI| GD32["GD32F103C8T6<br/>(ARM Cortex-M3)"]
        IMU["MPU9250 9-DOF IMU"] -->|I2C| GD32
        TOF["VL53L0X ToF / HC-SR04"] -->|I2C / Divider| GD32
        GD32 -->|Closed-Loop PID PWM| MOT["4x JGB37-520 12V<br/>333RPM Encoder Motors"]
    end

    NRF_TX <==>|"2.4 GHz RF Link (Ch 0-125)"| NRF_RX

3.1 Handheld Controller (MFC — Transmitter Node)

Subsystem	Component	Technical Details & Role	Build State
MCU	Espressif ESP32-S3-N16R8	Dual-core Xtensa® LX7 @ 240 MHz, 16 MB Quad SPI Flash, 8 MB Octal PSRAM.	Installed (Rev 0.1)
RF Telemetry	Nordic nRF24L01+ Module	2.4 GHz ISM band transceiver over shared SPI2_HOST.	Installed (Rev 0.1)
Bulk Decoupling	100 µF Electrolytic + Male Headers	Suppresses nRF24 PTX current spikes; modular header rails for peripherals.	Installed (Rev 0.1)
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" bench OLED).	Next Upgrade
Joysticks	2× K-Silver (KS) PS5 Hall-Effect Modules	3.3V active magnetic contactless gimbals for zero stick drift.	Next Upgrade
UI Input	KY-040 Rotary Encoder	Quadrature encoder (CLK, DT, SW) decoded in hardware via ESP32-S3 PCNT.	Bench Verified
Voice AI	MAX4466 Electret Microphone Module	Analog pre-amplifier with adjustable gain for cloud-connected AI voice assistant input.	Next Upgrade
Data Logging	Arduino Micro SD Card Module	SPI interface, formatted FAT32 for local telemetry and configuration logging.	Next Upgrade
Audio Output	1× Passive Buzzer + 2× Active Buzzers	Passive buzzer for melodies + 2× active buzzers for percussive UI clicks, driven by 2N2222 NPN Transistors.	Next Upgrade
Power System	Dual 18650 Li-ion + TP4056 + MT3608	Dual 18650 cells, TP4056 charger, MT3608 DC-DC boost converter (5V rail), 1N5817 Schottky & 1N4001 diodes, 100 nF ceramic caps.	Next Upgrade

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)

4.1 Current Verified Pin Allocation (firmware/main/mmcontroller.c)

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)

4.2 Planned Pin Allocation for Phase 2 Modules (Safe ESP32-S3 Matrix)

To avoid ESP32-S3 Octal Flash/PSRAM pins (GPIO 26–37), USB-OTG pins (GPIO 19–20), strapping pins (GPIO 0, 3, 45, 46), and ADC2 Wi-Fi conflicts, the remaining modules map cleanly to:

Upcoming Module	Signal	Recommended GPIO	Hardware Resource
K-Silver Hall Joystick 2	VRx2 / VRy2	GPIO 6 / GPIO 7	ADC1_CH5 / ADC1_CH6 (12 dB Atten)
MAX4466 Microphone	OUT (Analog)	GPIO 1	ADC1_CH0 (DMA / Oneshot audio sampling)
Battery Sense Divider	VBAT_SNS	GPIO 2	ADC1_CH1 (100kΩ / 100kΩ voltage divider)
MicroSD Card Module	CS_SD	GPIO 18	Shared SPI2_HOST Chip Select #3
Passive Buzzer (Melody)	BUZ_PWM	GPIO 38	LEDC Hardware Timer PWM via 2N2222
Active Buzzers 1 & 2	ACT_BUZ_1/2	GPIO 39 / GPIO 40	Digital Output via 2N2222 NPN low-side switches
Toggle / Slide Switches	SW_MODE	GPIO 41 / GPIO 42	Digital Input (GPIO_PULLUP_ENABLE)

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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 carbon 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 (alongside a 100 nF ceramic cap for high-frequency noise) to prevent 3.3V rail brown-outs during PTX transmission bursts.
5. 2N2222 Base Resistor & Flyback Protection: Always place a 1 kΩ series resistor between the ESP32-S3 GPIO pin and the Base (B) of each 2N2222 NPN transistor (an unresisted BJT base clamps the GPIO to 0.7V and draws excessive current). Place a 1N4001 flyback diode in reverse-parallel across inductive buzzer coils.
6. Multi-Slave SPI Bus Initialization Rule: When sharing SPI2_HOST across nRF24L01+ (GPIO 14), TFT Display (GPIO 10), and MicroSD (GPIO 18), configure all three CS pins as outputs and drive them HIGH (1) prior to initializing the first SPI device so uninitialized slaves do not corrupt MISO (GPIO 13).

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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 once the CS-equipped TFT module is wired. (Note: Verify whether the 1.8" PCB uses the ST7789 or ST7735S driver IC on arrival; both use identical SPI wiring and esp_lcd panel APIs).
2. MicroSD Card SPI & FATFS Setup: Configure the Arduino MicroSD card module on the shared 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 Rev 0.1 Baseline)
│   ├── 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              # Rev 0.1 carrier schematic (ESP32-S3, nRF24L01+, 100uF cap)
│   └── mfc-1.kicad_pcb              # Board layout & routing rules
├── images/                          # Rev 0.1 early prototype photography & vector schematic
│   ├── TOP_VIEW.png                 # Early build (Rev 0.1) carrier top view
│   ├── SIDE_VIEW_WITH_ANTENNA.png   # Early build (Rev 0.1) RF antenna & profile view
│   ├── BOTTOM_VIEW.png              # Early build (Rev 0.1) perfboard underside wiring
│   └── mfc-1.svg                    # Vector export of Rev 0.1 KiCad schematic
├── .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