NXP Line Follower - Hackathon 2026

This repository contains the control logic and hardware configuration for an autonomous line-following robot, developed during the NXP Hardware Hackathon held at the University of Bucharest.

🏆 Result: 9th Place out of 16 teams
⏱️ Best Lap Time: 20.6 seconds

📸 Project Showcase

⚙️ Hardware Overview

Based on the official NXP Cup Line Follower kit, the robot was assembled and programmed using the following components:

• Microcontroller: NXP FRDM-MCXN947 Development Board (Arm Cortex-M33 @ 150 MHz)
• Custom Shield: NXPCUP-Shield-FRDM-MCXN947
• Sensors: 8x Infrared reflective sensors with LM339 comparators (Digital 0/1 output)
• Actuators: 2x DC Geared Motors (25GA-370) driven by 2x DRV8833 Dual H-Bridge motor drivers
• Power Management: 7.4V 2200mAh 2S LiPo battery regulated to 5V via MP1584EN step-down converter

🧠 Control System & Logic

The robot's firmware is implemented in bare-metal C. It utilizes a combination of digital signal processing and control theory to maintain high speeds while ensuring stability.

1. Position Estimation (Weighted Average)

Instead of using simple binary states, the algorithm processes the 8-bit sensor array into a continuous error value:

• Weighted Sum: Each sensor is assigned a weight (0 to 7000). The calculate_position function computes a weighted average of all active sensors to determine the line's center.
• Granularity: This allows for precise error calculation even when the line is between two sensors, enabling smoother steering corrections.

2. Steering Control (PD Loop)

A Proportional-Derivative (PD) controller is used to manage the robot's heading:

• Proportional ($K_p$): Corrects the current error relative to the center.
• Derivative ($K_d$): Predicts future error by calculating the rate of change (delta_error), effectively dampening oscillations and preventing oversteering at high speeds.

3. Slew Rate Limiter & Traction Control

To maintain physical stability and prevent wheel slip:

• Acceleration Ramp: The actual_base_speed does not jump instantly to the target. It increments by a fixed ACCEL_STEP every cycle (2ms), mimicking a Slew Rate Limiter.
• Instant Deceleration: While acceleration is gradual to maintain traction, the system allows for near-instant power cuts when a sharp curve or emergency braking is required.

4. Predictive Active Braking

The system "anticipates" sharp corners by monitoring the derivative of the error:

• Brake Penalty: A Kd_Brake multiplier is applied to the target speed based on the magnitude of change in error (abs_delta).
• Outcome: The robot automatically slows down before entering a sharp turn and accelerates back to MAX_SPEED on straights.

5. Recovery Logic (Blind Pivoting)

If the line is completely lost (e.g., during an aggressive maneuver):

• Memory-Based Recovery: The robot remembers the last_position before the loss.
• Pivot Search: It performs a stationary pivot at PIVOT_SPEED in the direction where the line was last seen until the sensor array re-acquires the track.

🚀 Repository Structure

• source/ - Contains the main control logic (main.c) and configuration headers.
• nxpcup-linefollower.mex - The NXP Config Tools file detailing pin routing and clock setups.

📚 Resources & Documentation

• NXP Cup Line Follower Official Docs - The technical reference, hardware schematics, and SDK guidelines provided by NXP used to assemble the kit and develop the control algorithms.