trackedbot

Main Controller Board - Arduino Uno R3 (ATmega328P)

Hardware reference, component architecture, pinout, and configuration guide for the Arduino Uno R3 microcontroller development board used as the main controller in the tracked_bot platform.

This board features a Microchip ATmega328P primary motion microcontroller clocked at 16 MHz alongside an onboard USB-to-UART serial interface (ATmega16U2 or CH340G) providing deterministic serial communication to host controllers at 115200 baud.

📋 Table of Contents

  1. Hardware Overview & Key Components
  2. Datasheet References
  3. Component Specifications
  4. Serial UART Communication Architecture
  5. Complete Pinout and Signal Routing
  6. Operational Workflows (Programming & Running)
  7. Hardware Interconnection Architecture
  8. Board Variants & Hardware Compatibility

🔧 Hardware Overview & Key Components

The Arduino Uno R3 provides a robust, single-microcontroller embedded control platform:

  1. Primary Motion Controller (ATmega328P):
    • 8-bit AVR RISC microcontroller clocked at 16 MHz via external crystal resonator.
    • Handles real-time motor control (Timer0 and Timer2 Fast PWM), 74HC595 shift register direction timing, periodic telemetry reporting, and differential skid-steering kinematics.
    • Runs deterministic, bare-metal C firmware without RTOS overhead.
  2. USB-to-UART Interface (ATmega16U2 / CH340G):
    • Provides USB connectivity to a host development PC, single-board computer (e.g. Raspberry Pi), or ROS navigation node.
    • Bridges host serial commands directly to the ATmega328P hardware USART0 (PD0/RX, PD1/TX) at 115200 baud (8-N-1).
    • Handles automatic DTR reset for bootloader synchronization during firmware flashing.
  3. Power Regulation & Distribution:
    • 5.0 V on-board linear regulator (powered via USB 5V or external VIN 7–12V rail).
    • Onboard 3.3 V low-dropout (LDO) regulator providing auxiliary current for low-voltage sensors.

📚 Datasheet References

Original manufacturer datasheets for the core integrated circuits on this board are preserved in the repository:

⚡ Component Specifications

Feature Primary Controller (ATmega328P)
Architecture 8-bit AVR RISC
Clock Frequency 16 MHz (external crystal)
Operating Voltage 5.0 V DC
Flash Memory 32 KB (0.5 KB used by Optiboot bootloader)
SRAM 2 KB internal SRAM
EEPROM 1 KB internal EEPROM
Timers 2x 8-bit (Timer0, Timer2), 1x 16-bit (Timer1)
Hardware Serial (UART) 1x USART (PD0/RXD, PD1/TXD)
I/O Logic Levels 5 V TTL/CMOS
Analog Inputs 6 channels (10-bit ADC, A0–A5)
Interrupts External (INT0 on D2, INT1 on D3), Pin Change (PCINT0..PCINT23)

🔌 Serial UART Communication Architecture

All communication between the robot firmware and the host controller is conducted strictly over the hardware USART0 interface:

Incoming serial frames are ingested via the USART_RX_vect interrupt into a lock-free Single-Producer Single-Consumer (SPSC) ring buffer, decoded by a 5-state finite state machine (FSM), and dispatched deterministically in the main loop.

📌 Complete Pinout and Signal Routing

The headers on the Arduino Uno R3 provide standard female sockets that mate directly with the L293D Motor Shield. The table below details signal routing and dedicated functions within tracked_bot:

Digital Pins (D0 - D13)

Pin AVR Port Onboard Connection Role in tracked_bot
D0 (RX) PD0 ATmega328P USART RX USART0 RX: Serial binary command reception from Host
D1 (TX) PD1 ATmega328P USART TX USART0 TX: Serial binary telemetry transmission to Host
D2 PD2 Header pin FREE GPIO: External Interrupt 0 (INT0), sensors, encoders
D3 PD3 Header pin / L293D PWM2B Reserved (Timer2 OC2B for Motor 2 PWM on shield)
D4 PD4 Header pin / L293D DIR_CLK 74HC595 Shift Clock: Clock line for direction register
D5 PD5 Header pin / L293D PWM0B Reserved (Timer0 OC0B for Motor 4 PWM on shield)
D6 PD6 Header pin / L293D PWM0A Left Track PWM Speed: Timer0 OC0A Fast PWM
D7 PD7 Header pin / L293D DIR_EN 74HC595 Output Enable: Active-low output buffer enable (~OE)
D8 PB0 Header pin / L293D DIR_SER 74HC595 Serial Data: Direction bit data line (SER)
D9 PB1 Header pin / L293D PWM1A Reserved for Pan-Tilt Servo 2 (Timer1 OC1A)
D10 PB2 Header pin / L293D PWM1B Reserved for Pan-Tilt Servo 1 (Timer1 OC1B)
D11 PB3 Header pin / L293D PWM2A Right Track PWM Speed: Timer2 OC2A Fast PWM
D12 PB4 Header pin / L293D DIR_LATCH 74HC595 Storage Latch: Latches direction bits to outputs (RCLK)
D13 PB5 Header pin / Onboard SCK LED Status Heartbeat LED: Built-in diagnostic LED toggle

Analog Pins (A0 - A5 / D14 - D19)

All analog pins pass directly through the L293D motor shield to top breakout pads:

Pin AVR Port Alternative Functions Dedicated Purpose in tracked_bot
A0 PC0 ADC0 / PCINT8 Battery Voltage Sense: 4:1 resistive divider monitoring 2S battery pack
A1 PC1 ADC1 / PCINT9 HC-SR04 Ultrasonic Trigger: Pulse generator
A2 PC2 ADC2 / PCINT10 HC-SR04 Ultrasonic Echo: Pulse duration measurement
A3 PC3 ADC3 / PCINT11 Auxiliary GPIO / Analog Input
A4 PC4 ADC4 / I2C SDA I2C Bus SDA: IMU gyroscope/accelerometer (MPU-6050) / OLED display
A5 PC5 ADC5 / I2C SCL I2C Bus SCL: IMU gyroscope/accelerometer (MPU-6050) / OLED display

🚀 Operational Workflows (Programming & Running)

Workflow 1: Flashing ATmega328P Firmware (tracked_bot)

To compile and flash the bare-metal AVR C firmware onto the ATmega328P:

  1. Disconnect or turn off the robot’s external motor battery power.
  2. Connect the Arduino Uno R3 to your host computer via a standard USB Type-B cable.
  3. Verify the serial port device node (e.g. /dev/ttyUSB0 or /dev/ttyACM0 on Linux): 
    ls -l /dev/ttyUSB* /dev/ttyACM*
  4. Build and flash the firmware image using make: 
    make -C sw/trackedbot/build flash PORT=/dev/ttyUSB0
  5. avrdude will synchronize with the Optiboot / STK500v1 bootloader at 115200 baud and program the Flash memory.

Workflow 2: Normal Robot Operation (UART Control)

After flashing the firmware:

  1. Mount the L293D Motor Shield firmly onto the Arduino Uno R3 headers.
  2. Connect external 2S Li-Ion / LiPo battery power according to the power_supply.md guide.
  3. Connect the host controller (PC, Raspberry Pi, or embedded SBC) to the Arduino Uno R3 via:
    • USB Cable: Direct connection to the Arduino USB port (creating a virtual COM / tty port on the host).
    • Direct TTL Serial: Connect host TX to D0 (RX) and host RX to D1 (TX) with a common ground (5V level tolerant).
  4. Open the serial port at 115200 baud (8-N-1) and begin transmitting binary protocol frames as specified in sw/protocol.md.

⚡ Hardware Interconnection Architecture

flowchart TD
    subgraph Host ["<b>Development PC / Host Controller</b>"]
        CLIENT["<b>Control Application</b><br/>CLI / Web GUI / ROS Node"]
        USB_PORT["<b>USB Host Controller</b><br/>Type-B / Virtual COM Port"]
        CLIENT <-->|"Serial Data Stream"| USB_PORT
    end

    subgraph UnoBoard ["<b>Arduino Uno R3 Main Board</b>"]
        direction TB

        subgraph CommLayer ["USB-to-UART Bridge"]
            USB_UART["<b>ATmega16U2 / CH340G</b><br/>USB-to-Serial Converter"]
        end

        ATMEGA["<b>ATmega328P MCU Core</b><br/>Primary Real-Time Motion Engine (16 MHz)"]

        USB_UART <-->|"Hardware USART0 (D0/RX, D1/TX)"| ATMEGA
    end

    subgraph MotorShield ["<b>L293D Motor Driver Shield</b>"]
        direction TB
        L293D_CTRL["<b>74HC595 Shift Register</b><br/>Direction Multiplexer (Q0..Q7)"]
        L293D_DRV["<b>Dual L293D H-Bridges</b><br/>Motor Driver ICs (IC1, IC2)"]
        L293D_CTRL --> L293D_DRV
    end

    subgraph Chassis ["<b>Locomotion Platform: T101 Aluminum Chassis</b>"]
        MOTOR_R["<b>Right Track DC Gearmotor</b><br/>Channel M1"]
        MOTOR_L["<b>Left Track DC Gearmotor</b><br/>Channel M3"]
        TRACKS["<b>Modular Caterpillar Tracks</b><br/>POM Interlocking Links"]
        MOTOR_R --> TRACKS
        MOTOR_L --> TRACKS
    end

    USB_PORT ==>|"USB Cable / Serial UART (115200 8-N-1)"| USB_UART

    ATMEGA -->|"Timer0 Fast PWM D6 (Left Speed)"| L293D_DRV
    ATMEGA -->|"Timer2 Fast PWM D11 (Right Speed)"| L293D_DRV
    ATMEGA -->|"Direction Bus D4/D7/D8/D12"| L293D_CTRL
    ATMEGA -.->|"Sensors & ADC Bus A0..A5"| MotorShield

    L293D_DRV ==>|"PWM Motor Drive M1"| MOTOR_R
    L293D_DRV ==>|"PWM Motor Drive M3"| MOTOR_L

    classDef hostStyle fill:#0f766e,stroke:#14b8a6,stroke-width:2px,color:#ffffff;
    classDef commStyle fill:#312e81,stroke:#818cf8,stroke-width:2px,color:#ffffff;
    classDef mcuStyle fill:#0c4a6e,stroke:#38bdf8,stroke-width:2px,color:#ffffff;
    classDef shieldStyle fill:#831843,stroke:#f472b6,stroke-width:2px,color:#ffffff;
    classDef motorStyle fill:#701a75,stroke:#e879f9,stroke-width:2px,color:#ffffff;

    class CLIENT,USB_PORT hostStyle;
    class USB_UART commStyle;
    class ATMEGA mcuStyle;
    class L293D_CTRL,L293D_DRV shieldStyle;
    class MOTOR_R,MOTOR_L,TRACKS motorStyle;

    style Host fill:none,stroke:#14b8a6,stroke-width:2px,stroke-dasharray: 4 4
    style UnoBoard fill:none,stroke:#38bdf8,stroke-width:2px,stroke-dasharray: 4 4
    style CommLayer fill:none,stroke:#818cf8,stroke-width:1px
    style MotorShield fill:none,stroke:#f472b6,stroke-width:2px,stroke-dasharray: 4 4
    style Chassis fill:none,stroke:#e879f9,stroke-width:2px,stroke-dasharray: 4 4

For motor shield driver circuits and register assignments, refer to motor_shield.md. For power rail wiring and battery safety, refer to power_supply.md.

🏷️ Board Variants & Hardware Compatibility

The tracked_bot firmware is compatible with standard Arduino Uno R3 boards and equivalent open-source hardware designs:

  1. Official Arduino Uno R3: Uses the ATmega16U2 USB interface chip (enumerates as /dev/ttyACM* on Linux).
  2. Uno R3 Compatible / Clones: Typically use the WCH CH340G USB interface chip (enumerates as /dev/ttyUSB* on Linux). Both versions provide identical 5V TTL serial connections to the ATmega328P USART0 core.
  3. 100% Shield Compatibility: The physical header footprint, pin spacing, and 5V logic signaling are identical across all Uno R3 variants, ensuring seamless stacking with the L293D Motor Shield.
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