Arduino Robot Project Build: L298N vs TB6612FNG Motor Driver Decision Guide

Building a reliable Arduino robot project usually stalls at the motor driver selection. You pick a chassis, wire up an ultrasonic sensor, and then face the classic dilemma: do you use the bulky, cheap L298N, or the efficient, compact TB6612FNG? The wrong choice leads to stalled motors, logic brownouts, and hours of frustrating debugging.

This guide cuts through the guesswork. We will make a concrete hardware decision, wire the system with exact pin mappings, and flash complete, compilable C++ code targeting the Arduino Uno R3 (ATmega328P DIP). Finally, we will cover the exact error strings and hardware symptoms you will encounter when things go wrong.

The Core Decision: L298N vs TB6612FNG

Before buying parts, you must match your motor driver to your power source. The L298N uses bipolar junction transistors (BJTs), resulting in a massive 2V to 3V voltage drop and poor thermal efficiency. The TB6612FNG uses MOSFETs, dropping only about 0.5V and running cool under load.

Exact Parts List and Chassis Specs

Here is the exact bill of materials (BOM) for a 2WD obstacle-avoiding platform. Prices reflect standard hobbyist supplier rates.

Pin Mapping and Wiring Walkthrough

The most common point of failure in an Arduino robot project is a floating ground or a misrouted PWM signal. The TB6612FNG requires both a logic voltage (VCC) and a motor voltage (VM).

Numbered Wiring Steps

1. Establish Common Ground: Connect the negative terminal of your 2S LiPo battery pack directly to the Arduino Uno GND pin, and then to the TB6612FNG GND pins. If logic and motor grounds are not bonded, the driver will not interpret logic signals.
2. Wire Motor Power: Connect the LiPo positive terminal to the TB6612FNG VM pin. Do not route motor power through the Arduino's Vin or barrel jack; the onboard linear regulator will overheat and trigger thermal shutdown at currents above 200mA.
3. Wire Logic Power: Connect the Arduino 5V pin to the TB6612FNG VCC pin.
4. Connect Sensor: Wire the HC-SR04 VCC to Arduino 5V, GND to GND, Trig to Digital 9, and Echo to Digital 10.
5. Verify Standby: Ensure the STBY pin is wired to Digital 4. The TB6612FNG ignores all inputs if STBY is LOW.

Complete Compilable Code for Arduino Uno R3

This code targets the Arduino Uno R3 (AVR ATmega328P). It uses the NewPing library to handle ultrasonic sensor timeouts without blocking the main loop, and includes an internal VCC brownout check to protect the microcontroller from voltage sags caused by motor stalls.

#include <NewPing.h>

// --- PIN DEFINITIONS ---
#define TRIG_PIN 9
#define ECHO_PIN 10
#define PWMA 5
#define AIN1 7
#define AIN2 8
#define PWMB 6
#define BIN1 11
#define BIN2 12
#define STBY 4

// --- SENSOR CONFIG ---
#define MAX_DISTANCE 200
#define OBSTACLE_THRESHOLD 20 // cm

NewPing sonar(TRIG_PIN, ECHO_PIN, MAX_DISTANCE);

// --- MOTOR SPEEDS ---
const int SPEED_FORWARD = 200; // 0-255 PWM
const int SPEED_TURN = 150;

void setup() {
  Serial.begin(115200);
  
  pinMode(AIN1, OUTPUT); pinMode(AIN2, OUTPUT);
  pinMode(BIN1, OUTPUT); pinMode(BIN2, OUTPUT);
  pinMode(PWMA, OUTPUT); pinMode(PWMB, OUTPUT);
  pinMode(STBY, OUTPUT);
  
  digitalWrite(STBY, HIGH); // Wake up motor driver
  stopMotors();
  Serial.println(F("System Initialized. Starting navigation."));
}

void loop() {
  // 1. Hardware Safety Check: Read internal VCC to detect brownouts
  long vcc = readVcc();
  if (vcc < 4500) {
    Serial.println(F("ERR: VCC_BROWNOUT < 4.5V. Motors halted."));
    stopMotors();
    delay(1000);
    return; // Skip navigation loop to save power
  }

  // 2. Sensor Reading (Non-blocking ping)
  delay(30); // Wait for ping to clear
  int dist = sonar.ping_cm();
  
  // 3. Navigation Logic
  if (dist > 0 && dist < OBSTACLE_THRESHOLD) {
    Serial.print(F("Obstacle at ")); Serial.print(dist); Serial.println(F("cm. Turning."));
    turnRight();
    delay(400); // Time to clear obstacle
  } else {
    moveForward();
  }
}

// --- MOTOR CONTROL FUNCTIONS ---
void moveForward() {
  digitalWrite(AIN1, HIGH); digitalWrite(AIN2, LOW);
  digitalWrite(BIN1, HIGH); digitalWrite(BIN2, LOW);
  analogWrite(PWMA, SPEED_FORWARD);
  analogWrite(PWMB, SPEED_FORWARD);
}

void turnRight() {
  digitalWrite(AIN1, HIGH); digitalWrite(AIN2, LOW); // Left motor forward
  digitalWrite(BIN1, LOW); digitalWrite(BIN2, HIGH); // Right motor backward
  analogWrite(PWMA, SPEED_TURN);
  analogWrite(PWMB, SPEED_TURN);
}

void stopMotors() {
  digitalWrite(AIN1, LOW); digitalWrite(AIN2, LOW);
  digitalWrite(BIN1, LOW); digitalWrite(BIN2, LOW);
  analogWrite(PWMA, 0);
  analogWrite(PWMB, 0);
}

// --- BROWNOUT DETECTION (AVR SPECIFIC) ---
long readVcc() {
  long result;
  // Read 1.1V reference against AVcc
  ADMUX = _BV(REFS0) | _BV(MUX3) | _BV(MUX2) | _BV(MUX1);
  delay(2); // Wait for Vref to settle
  ADCSRA |= _BV(ADSC); // Start conversion
  while (bit_is_set(ADCSRA, ADSC));
  result = ADC;
  result = 1125300L / result; // Calculate Vcc (in mV)
  return result;
}

Debugging: First 3 Checks and Exact Error Strings

When your Arduino robot project fails to move, do not start rewriting code. Hardware and power issues account for 90% of robotics failures. Here is your decision path for debugging.

The First 3 Things to Check

1. Verify the STBY Pin: Use a multimeter to check the voltage on the TB6612FNG STBY pin. It must read ~5V (HIGH). If it is floating or LOW, the H-bridge is physically disabled.
2. Check Common Ground: Measure resistance between the Arduino GND pin and the battery negative terminal. It should read < 1 ohm. If it reads open (OL), your logic and motor circuits are isolated, and the driver cannot read PWM signals.
3. Measure VM Under Load: Measure the voltage at the TB6612FNG VM pin while the motors are trying to spin. If it drops below 4.5V, your battery C-rating is too low, or your wires are too thin (use at least 18 AWG for motor power).

Ranked Causes for Exact Error Strings

How to Extend or Simplify the Build

Depending on your skill level and project timeline, you can scale this Arduino robot project up or down without redesigning the core chassis.

How to Simplify (For Beginners or Quick Demos)

• Drop the Ultrasonic Sensor: Replace the HC-SR04 with two mechanical limit switches (bump sensors) wired to digital inputs with internal pull-up resistors. This eliminates timing bugs and library dependencies entirely.
• Use a 4x AA Battery Pack: Switch to standard alkaline or NiMH AA batteries and swap the TB6612FNG for an L298N. This removes the need for LiPo safety protocols and specialized chargers, though runtime will drop by 60%.

How to Extend (For Advanced Makers)

• Add Dead Reckoning: Mount an MPU6050 IMU (I2C) to the chassis. By integrating accelerometer data, you can detect when the robot gets stuck against a wall (high acceleration, zero wheel encoder ticks) and trigger a reverse maneuver.
• Upgrade to ESP32 for Telemetry: Swap the Arduino Uno R3 for an ESP32-DevKitC V4. The ESP32 is 3.3V logic, so you must use a logic level shifter for the HC-SR04 (or switch to an RCWL-0516 microwave radar sensor which is 3.3V native). This allows you to stream sensor data over MQTT to a dashboard while the robot navigates.
• Implement PID Control: Replace the hardcoded delay() turns with a PID controller reading from wheel encoders. This allows the robot to drive in a perfectly straight line even if one TT gearmotor has slightly higher internal friction than the other.