MotorEncoder Library

Arduino & Raspberry Pi Pico Quadrature Encoder Reader

Author: Prince Kumar (TA - Mechatronics)

Repo: GitHub – 2ch-motor-encoder

Features

• Read direction (FWD/REV)
• Get shaft RPM & shaft angle
• Compute output RPM after gearbox
• Calculate wheel speed in m/s and km/h
• Auto-detect gear ratio if motor-rated RPM is given
• Supports active-high & active-low encoders

Works with the following encoder types:

Encoder Type	Signal Type	Recommended Placement	Notes
Mechanical Switch	Digital (active-high/low)	Near wheel shaft	Good for low-speed experiments; debounce may be required
Optical / Photoelectric Slot	Digital (active-high/low)	Motor shaft or wheel	Fast response, suitable for robotics projects
Magnetic Hall-Effect	Digital (active-high/low)	Close to rotating magnet	Durable, works in dusty/dirty environments
Incremental Rotary	Digital quadrature	Motor shaft	Provides high resolution angle and speed

Quick Start

1. Connect encoder pins:

   • Channel A → GPIO2
   • Channel B → GPIO3

2. Install library: download ZIP → Arduino IDE → Sketch > Include Library > Add .ZIP Library.

3. Load example: File > Examples > MotorEncoder > BasicUsage

4. Open Serial Monitor at 115200 baud.

Usage Example

#include <MotorEncoder.h>

MotorEncoder encoder;

void setup() {
  Serial.begin(115200);
  encoder.begin(2, 3, 600, 0, 100.0, 300, false, true);
}

void loop() {
  EncoderData data = encoder.read();
  Serial.println(data.shaftRPM);
}

Parameters

• pulsesPerRev: PPR from datasheet (0 if unknown)
• gearRatio: if 0, auto-calculated when motorRatedRPM is given
• wheelDiameter_mm: wheel outer diameter
• motorRatedRPM: vendor RPM (after gearbox)
• invertDirection: true if gearbox inverts motion
• activeHigh: true for standard encoders, false for switch-based

Output Data (EncoderData struct)

Field	Unit	Description
tickCount	ticks	Raw pulse count
directionForward	bool	Rotation direction
shaftRPM	RPM	Motor shaft speed
shaftAngleDeg	°	Shaft angular position
outputRPM	RPM	Gearbox output speed
wheelSpeed_mps	m/s	Linear speed
wheelSpeed_kmph	km/h	Linear speed
wheelAngleDeg	°	Wheel angular position

Note: Home Position / Initial Tick Value

By default, the library considers the encoder position as zero on startup.

If you want to start from a custom position instead of zero (for example, to set a known home/reference point), you can use the following snippet:

#include <MotorEncoder.h>

MotorEncoder encoder;

void setup() {
  Serial.begin(115200);
  encoder.begin(2, 3, 600, 0, 100.0, 300, false, true);

  // Set a custom initial tick count (e.g., home position)
  encoder.setInitialTicks(100);  // starts counting from 100 ticks instead of 0
}

void loop() {
  EncoderData data = encoder.read();
  Serial.print("Ticks: "); Serial.println(data.tickCount);
}

This allows to define a reference position, which can be useful in robotics, line-followers, or practical lab setups where the motor/wheel does not always start from zero.

Applications

• Robotics
• Differential drive control
• AGVs & line-followers
• Mechatronics labs (teaching tool)

References and Further Reading

• Quadrature Encoder Basics – Video 1 (YouTube)
• Type of Encoder as Absolute or Incremental – Video 2 (YouTube)
• Arduino Official Interrupt Reference
• Quadrature Encoder Wikipedia Article
• Pico Arduino Core Documentation
• PJRC Encoder Library (for comparison)

These links give background on how encoders work, how interrupts are handled on Arduino-style boards, and how the common Encoder library implements similar functionality.

License

MIT License – Free to use for projects, teaching, and research.