Micro-PP Autonomous Maze Solver

ESP32-based autonomous robot that follows a white line on a black surface, explores a maze using the Left-Hand Rule, and replays the optimized shortest path at full speed.

---

Table of Contents

• Hardware Components
• Project Structure
• Pin Mapping
• Power Distribution
• Getting Started
• How It Works
• Tuning Guide
• Docs

---

Hardware Components

#	Component	Qty	Role
1	N20-6V-600 RPM Micro Metal Gear Motor	2	Left and right drive motors
2	SmartElex RLS-08 Analog & Digital Line Sensor Array	1	8-channel white-line detection
3	LM2596S DC-DC Buck Converter Power Supply	2	Motor rail (6 V) and logic rail (5 V)
4	Motor Driver TB6612FNG Module	1	Dual H-bridge for both N20 motors
5	Performance Ultra Small Volume 3 PI Matching	1	RF impedance matching (antenna)
6	Performance Ultra L298N	1	Auxiliary motor driver (reserved)
7	ESP32 DevKit V1	1	Main microcontroller
8	Battery	1	Main power source (7.4 V 2S LiPo)
9	8x17 Breadboard	2	Power bus distribution

---

Project Structure

micropp/
├── platformio.ini                        # PlatformIO build config (ESP32 DevKit V1)
├── README.md                             # This file
├── .gitignore
├── src/
│   ├── main.cpp                          # Entry point: setup + loop + state trigger
│   ├── config.h                          # ALL pin assignments and tuning constants
│   ├── motors/
│   │   ├── motor_driver.h               # TB6612FNG driver interface
│   │   └── motor_driver.cpp             # PWM, direction, brake, pivot turns
│   ├── sensors/
│   │   ├── line_sensor.h                # RLS-08 sensor array interface
│   │   └── line_sensor.cpp              # Mux read, calibration, position calc
│   └── navigation/
│       ├── pid_controller.h             # Generic PID interface
│       ├── pid_controller.cpp           # Time-scaled PID with anti-windup
│       ├── maze_solver.h                # Maze state machine interface
│       └── maze_solver.cpp              # Left-Hand Rule + optimization + speed run
└── docs/
    ├── wiring_diagram.md                # Full GPIO tables and power rail notes
    └── algorithm.md                     # Algorithm explanation and state machine

Quick Links to Source Files

File	Purpose
src/config.h	Every pin, speed, PID gain, and timing constant in one place
src/main.cpp	Boot sequence, button trigger, LED status, main loop
src/motors/motor_driver.h	Motor driver public API
src/motors/motor_driver.cpp	LEDC PWM + TB6612FNG logic
src/sensors/line_sensor.h	Sensor array public API
src/sensors/line_sensor.cpp	8-channel mux, calibration, position error
src/navigation/pid_controller.h	PID interface
src/navigation/pid_controller.cpp	PID with anti-windup and output clamping
src/navigation/maze_solver.h	State machine interface
src/navigation/maze_solver.cpp	Left-Hand Rule, path optimization, speed run
docs/wiring_diagram.md	Pin tables, power distribution, LM2596S setup
docs/algorithm.md	Full algorithm walkthrough with examples

---

Pin Mapping

ESP32 DevKit V1 to TB6612FNG Motor Driver

ESP32 GPIO	TB6612FNG	Description
GPIO 25	AIN1	Motor A (Left) direction pin 1
GPIO 26	AIN2	Motor A (Left) direction pin 2
GPIO 32	PWMA	Motor A speed (PWM)
GPIO 27	BIN1	Motor B (Right) direction pin 1
GPIO 14	BIN2	Motor B (Right) direction pin 2
GPIO 33	PWMB	Motor B speed (PWM)
GPIO 13	STBY	Driver standby (HIGH = enabled)
3.3 V	VCC	Logic supply
GND	GND	Common ground

ESP32 DevKit V1 to SmartElex RLS-08 Sensor Array

ESP32 GPIO	RLS-08	Description
GPIO 36 (VP)	OUT / ANA	Analog multiplexer output
GPIO 34	S0	Channel select bit 0
GPIO 35	S1	Channel select bit 1
GPIO 4	S2	Channel select bit 2
5 V	VCC	Sensor power
GND	GND	Common ground

All adjustable pin assignments live in src/config.h. Change them there and the rest of the code follows automatically.

---

Power Distribution

Battery (7.4 V 2S LiPo)
    |
    +--[Switch]
         |
         +-- LM2596S #1 --> 6.0 V --> TB6612FNG VM  (motor power)
         |
         +-- LM2596S #2 --> 5.0 V --> ESP32 VIN
                                  --> RLS-08 VCC

All ground rails are tied together (battery, both buck converters, ESP32, motor driver, sensor array).

See docs/wiring_diagram.md for full detail and LM2596S adjustment instructions.

---

Getting Started

1. Install PlatformIO

Install the PlatformIO extension for VS Code.

2. Clone and Open

git clone https://github.com/theerthkr/micropp.git
cd micropp

Open the folder in VS Code. PlatformIO detects platformio.ini automatically.

3. Build

Click the Build button (checkmark icon in the PlatformIO toolbar) or run:

pio run

4. Flash

Connect the ESP32 DevKit V1 via USB, then click Upload or run:

pio run --target upload

5. Open Serial Monitor

pio device monitor --baud 115200

---

How It Works

The robot operates as a three-phase state machine. Full details are in docs/algorithm.md.

[IDLE] --> (BOOT button) --> [CALIBRATING] --> [EXPLORING] --> [OPTIMIZING] --> [SPEED_RUN] --> [FINISHED]

Phase 1 - Calibration

Press the BOOT button (GPIO 0) on the ESP32. The robot slowly spins in place while the RLS-08 sensor array records the minimum and maximum ADC reading for each of its 8 channels. This compensates for uneven sensor sensitivity and ambient lighting.

Phase 2 - Exploration (Left-Hand Rule)

The robot follows the white line using PID control and makes decisions at every intersection using this priority order:

LEFT  >  STRAIGHT  >  RIGHT  >  U-TURN

Every turn taken is recorded as L, R, S, or U. A dead end (no line detected) triggers an automatic U-turn.

Phase 3 - Path Optimization

The recorded turn sequence is compressed. Any triplet of the form X U Y (a turn, then a U-turn, then another turn) is a redundant detour and collapses into a single equivalent turn.

Pattern	Simplifies To
L U L	S
L U S	R
L U R	U
S U L	R
S U S	U
S U R	L
R U L	S
R U R	S
R U S	L

Passes repeat until no further simplification is possible.

Phase 4 - Speed Run

The robot replays the optimized turn sequence at MOTOR_MAX_SPEED without any turn-decision logic. PID line following remains active between intersections for accuracy.

---

Tuning Guide

All tuning constants are in src/config.h. Adjust and reflash.

Constant	Default	Effect
MOTOR_BASE_SPEED	130	Cruise speed during exploration
MOTOR_MAX_SPEED	200	Speed during the final speed run
MOTOR_TURN_SPEED	90	Speed used during point turns
PID_KP	0.035	Proportional gain - increase for faster correction
PID_KI	0.0001	Integral gain - reduces steady-state drift
PID_KD	0.18	Derivative gain - damps oscillation
TURN_90_MS	320	Milliseconds for a 90-degree pivot turn
TURN_180_MS	640	Milliseconds for a 180-degree U-turn

If the robot overshoots turns: decrease TURN_90_MS / TURN_180_MS. If the robot oscillates on the line: decrease PID_KP or increase PID_KD.

---

Docs

• docs/wiring_diagram.md - Complete pin tables, power rails, breadboard notes, LM2596S setup
• docs/algorithm.md - Left-Hand Rule, substitution table with worked example, state machine diagram

---

License

MIT License.