trackedbot

Main Controller Board - Uno+WiFi R3 (ATmega328P + ESP8266)

Hardware reference, component architecture, pinout, and configuration guide for the Uno+WiFi R3 hybrid development board (commonly marketed as TZT Uno WiFi R3, RobotDyn Uno+WiFi, or WeMos Uno WiFi R3 ATmega328P+ESP8266) used as the main controller in the tracked_bot platform.

This board integrates both a Microchip ATmega328P primary motion microcontroller and an Espressif ESP8266EX (32Mb flash) wireless communications coprocessor, alongside a CH340G USB-to-UART bridge on a single standard Arduino Uno R3 footprint.

📋 Table of Contents

  1. Hardware Overview & Key Components
  2. Datasheet References
  3. Component Specifications
  4. 8-Position DIP Switch Configuration
  5. Complete Pinout and Signal Routing
  6. Operational Workflows (Programming & Running)
  7. Hardware Interconnection Architecture

🔧 Hardware Overview & Key Components

The TZT Uno WiFi R3 replaces a multi-board stack with a dual-processor architecture:

  1. Primary Motion Controller (ATmega328P):
    • 8-bit AVR RISC microcontroller clocked at 16 MHz.
    • Handles real-time motor control (Timer0 Fast PWM), 74HC595 shift register direction timing, odometry, and differential steering kinematics.
    • Runs deterministic, bare-metal C firmware without RTOS overhead.
  2. Communications Coprocessor (ESP8266EX):
    • 32-bit Tensilica Xtensa LX106 processor (clocked at 80/160 MHz) with 32 Mbit (4 MB) external SPI flash memory.
    • Provides 802.11 b/g/n Wi-Fi connectivity (TCP/UDP, WebSocket, or HTTP REST server).
    • Manages network packet reception, telemetry broadcasting, and forwards commands to the ATmega328P via hardware USART at 9600 / 115200 baud.
  3. USB-UART Interface (CH340G):
    • Provides USB Type-B connectivity to a host development PC for firmware flashing and serial monitoring.
    • Multiplexed via an onboard 8-position DIP switch to connect either to the ATmega328P or the ESP8266.

📚 Datasheet References

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

⚡ Component Specifications

Feature Primary Controller (ATmega328P) Wi-Fi Coprocessor (ESP8266EX)
Architecture 8-bit AVR RISC 32-bit Tensilica Xtensa L106
Clock Frequency 16 MHz (external crystal) 80 MHz / 160 MHz
Operating Voltage 5.0 V DC 3.3 V DC (onboard LDO regulator)
Flash Memory 32 KB (0.5 KB used by bootloader) 4 MB (32 Mbit SPI Flash)
SRAM 2 KB internal SRAM ~50 KB usable RAM
EEPROM 1 KB internal EEPROM None (emulated in SPI flash sector)
Timers 2x 8-bit (Timer0, Timer2), 1x 16-bit (Timer1) System timers, Software PWM
Hardware Serial (UART) 1x USART (PD0/RX, PD1/TX) 1x Full UART (UART0), 1x TX-only (UART1)
I/O Logic Levels 5 V TTL/CMOS 3.3 V LVTTL (tolerant on UART via dividers)

🎛️ 8-Position DIP Switch Configuration

The onboard 8-position DIP switch physically routes the UART TX/RX lines between the CH340G USB converter, the ATmega328P microcontroller, and the ESP8266 Wi-Fi SoC:

Mode / Functionality SW1 SW2 SW3 SW4 SW5 SW6 SW7 SW8
Mode 1: Flash ATmega328P (make flash) OFF OFF ON ON OFF OFF OFF N/U
Mode 2: Normal Robot Operation (ATmega328P ↔ ESP8266) ON ON OFF OFF OFF OFF OFF N/U
Mode 3: Flash ESP8266 Firmware OFF OFF OFF OFF ON ON ON N/U
Mode 4: ESP8266 Serial Monitor Debug OFF OFF OFF OFF ON ON OFF N/U
Mode 5: All Modules Disconnected / Isolated OFF OFF OFF OFF OFF OFF OFF N/U

[!NOTE]

📌 Complete Pinout and Signal Routing

The headers on the TZT Uno WiFi R3 follow the standard Arduino Uno R3 footprint. The table below details the signal routing, onboard connections, and usage within tracked_bot:

Digital Pins (D0 - D13)

Pin AVR Port Onboard Connection Role in tracked_bot
D0 (RX) PD0 ATmega328P USART RX (DIP SW1/SW4) USART0 RX: Serial command stream from ESP8266
D1 (TX) PD1 ATmega328P USART TX (DIP SW2/SW3) USART0 TX: Serial telemetry stream to ESP8266
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 Right Track PWM Speed: Timer0 OC0B Fast PWM
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 Reserved (Timer2 OC2A for Motor 1 PWM on shield)
D12 PB4 Header pin / L293D DIR_LATCH 74HC595 Storage Latch: Latches direction bits to outputs (RCLK)
D13 PB5 Header pin / Onboard SCK LED FREE GPIO: SPI SCK / Built-in indicator LED

Analog Pins (A0 - A5 / D14 - D19)

All analog pins are uncommitted by the L293D motor shield and are available on the top header breakout:

Pin AVR Port Alternative Functions Dedicated Purpose in tracked_bot
A0 PC0 ADC0 / PCINT8 Battery Voltage Sense: 10:1 resistor divider to ADC0
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
A5 PC5 ADC5 / I2C SCL I2C Bus SCL: IMU gyroscope/accelerometer (MPU-6050) / OLED

🚀 Operational Workflows (Programming & Running)

Workflow 1: Flashing ATmega328P Firmware (tracked_bot)

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

  1. Disconnect or power down the robot’s external motor power supply.
  2. Set the 8-position DIP switch to Mode 1:
    • SW3 = ON, SW4 = ON
    • SW1, SW2, SW5, SW6, SW7, SW8 = OFF
  3. Connect the board to your development machine using a USB Type-B cable.
  4. Execute the build and flash target: 
    make -C sw/trackedbot/build flash PORT=/dev/ttyUSB0
  5. avrdude will synchronize with the optiboot / STK500v1 bootloader over /dev/ttyUSB0 at 115200 baud and flash the firmware image.

Workflow 2: Normal Robot Operation (Wireless Control)

After flashing the firmware:

  1. Disconnect the USB cable or switch the DIP switch with power off.
  2. Set the 8-position DIP switch to Mode 2:
    • SW1 = ON, SW2 = ON
    • SW3, SW4, SW5, SW6, SW7, SW8 = OFF
  3. Mount the L293D Motor Shield onto the board headers.
  4. Connect external battery power according to the power_supply.md guide.
  5. In this mode, ATmega328P pins D0 (RX) and D1 (TX) communicate directly with the ESP8266 UART at 9600 baud. The ESP8266 listens to Wi-Fi control packets and streams motion commands to the AVR core.

Workflow 3: Flashing ESP8266 Wi-Fi Firmware

When flashing an updated Wi-Fi firmware image or Arduino ESP8266 sketch:

  1. Set the 8-position DIP switch to Mode 3:
    • SW5 = ON, SW6 = ON, SW7 = ON
    • SW1, SW2, SW3, SW4, SW8 = OFF
  2. Connect USB to PC and run esptool.py (or Arduino IDE with board set to Generic ESP8266 Module).
  3. Upon completion, switch to Mode 4 (turn SW7 OFF) to monitor debug output, or Mode 2 to reconnect to ATmega328P.

⚡ Hardware Interconnection Architecture

                 +------------------------------------------------+
                 |              TZT Uno WiFi R3 Main Board        |
                 |                                                |
                 |   +------------+           +---------------+   |
 [USB to PC] ======> |   CH340G   |           |    ESP8266    |   |
                 |   |  USB-UART  |           |   Wi-Fi SoC   | <===> [Wi-Fi 802.11 b/g/n]
                 |   +-----+------+           +-------+-------+   |
                 |         |                          |           |
                 |         +----[ 8-Position DIP ]----+           |
                 |                      |                         |
                 |            (Serial D0/RX, D1/TX)               |
                 |                      |                         |
                 |              +-------v-------+                 |
                 |              |  ATmega328P   |                 |
                 |              | Primary MCU   |                 |
                 |              +-------+-------+                 |
                 +----------------------|-------------------------+
                                        |
                 (PWM D5/D6, Shift Reg D4/D7/D8/D12, ADC A0..A5)
                                        |
                 +----------------------v-------------------------+
                 |        L293D Motor Driver Shield               |
                 |  (IC1, IC2 H-Bridges + 74HC595 Shift Register) |
                 +------------------------------------------------+

For the 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 & Commercial Branding (TZT, RobotDyn, WeMos)

The hybrid Uno+WiFi R3 board is manufactured and distributed under several commercial brand names across various suppliers:

Important Clarification:

These are identical physical and electrical implementations of the same dual-processor architecture:

  1. Both Chips are Present: Every variant includes both the 8-bit Microchip ATmega328P (running at 5.0 V) and the 32-bit Espressif ESP8266EX (running at 3.3 V with 32 Mbit / 4 MB SPI flash) alongside the CH340G USB bridge.
  2. Standard 8-Position DIP Switch: All variants feature the same 8-position DIP switch controlling serial multiplexing between the USB interface, AVR core, and ESP8266 SoC.
  3. 100% Shield Compatibility: Because the physical Uno header pins (D0–D13, A0–A5) are wired directly to the ATmega328P, standard Arduino Uno shields (including the L293D Motor Shield) plug directly onto the board with full 5V TTL logic compatibility and exact Timer0/Timer2 hardware PWM pinout.
  4. Distinction from Standalone ESP8266 Boards: This dual-SoC board should not be confused with standalone ESP8266 boards (such as the legacy Wemos D1 R2 which contained only an ESP8266 without an ATmega328P). On this board, the ATmega328P runs the repository’s native real-time C firmware (sw/trackedbot), while the ESP8266 handles Wi-Fi networking and streams commands over hardware UART.
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