Let’s start with the basics: A rotary encoder is one of the most reliable ways to convert rotational motion into digital data — and it’s a key component in precision control systems. Whether you’re measuring shaft position, direction, or rotational speed, a well-selected encoder can make or break your project.
We’ll look at the two major types: incremental and absolute. I’ll explain the core differences — how one measures relative motion while the other knows its position even after a power loss — and when you’d want one over the other.
Wiring rotary encoders the right way is critical. I’ll walk you through the signal pins (A, B, Z for incremental, and multi-bit for absolute), grounding issues, pull-up resistors, and how to get clean readings with microcontrollers like Arduino or Raspberry Pi. No guesswork.
Rotary encoders are everywhere — from industrial servo motors and CNC spindles to the volume knob on your digital mixer. I’ve personally integrated them into robotic arms, stepper-controlled tools, and even a DIY camera slider. You’ll see just how versatile they are.
You’ll get plenty of visuals along the way — signal timing diagrams, connection illustrations, and real-world use cases. I built this guide with practical learners in mind, so you won’t get lost in jargon. Whether you’re troubleshooting noisy signals or choosing the baumer encoder for your setup, you’re in the right place.
What Is a Rotary Encoder and How Does It Work?
A rotary encoder is an electromechanical device that converts the angular position or rotational motion of a shaft into digital signals. These signals are then interpreted by a control system — such as a microcontroller, PLC, or motor driver — to determine position, speed, direction, or even distance traveled.
Rotary encoders are widely used in industrial automation, robotics, consumer electronics, 3D printers, and automotive systems. They provide precise feedback for controlling motors, navigating user interfaces, or automating complex mechanical operations. If you’ve ever turned a volume knob on a digital audio interface or watched a robot arm position itself with incredible accuracy, there’s a good chance a rotary encoder was behind the scenes.
Core Components of a Rotary Encoder
Even though rotary encoders look compact from the outside, they contain an elegant internal mechanism. Here are the essential parts:
Rotating Shaft: This is the part that physically rotates and transmits motion from the system it’s attached to — like a motor, gear, or user-controlled knob.
Code Disc (or Patterned Disc): Typically made of glass or plastic, this disc is etched or printed with lines, slots, or reflective patterns. As the shaft spins, this disc spins with it.
Optical Sensor / Photodiode / LED Pair: This sensor shines light through or reflects it off the disc. As the patterned disc moves, the sensor detects changes in light and converts them into a stream of high and low signals — digital pulses.
In magnetic encoders, the optical system is replaced with a magnet and Hall-effect sensors, which are more robust in harsh or dirty environments.
The signals generated are sent through output channels — typically Channel A and Channel B, and sometimes a Z-index pulse that marks the zero/reference point in a full revolution.
What Is PPR (Pulses Per Revolution)?
One of the most important characteristics of an incremental rotary encoder is PPR, or Pulses Per Revolution. This value determines the resolution of the encoder — in other words, how many digital signals are generated for one full 360° rotation of the shaft.
Think of PPR as the number of “ticks” per turn:
A 100 PPR encoder sends out 100 signal pulses per full rotation.
A 1000 PPR encoder gives you 10× more detail — ideal for high-precision positioning.
Why does this matter? The higher the PPR, the more precisely the system can track position, speed, and acceleration. This is crucial in applications like:
Motor control (especially servo motors)
CNC machines and 3D printersRobotics and automation arms
Camera sliders and pan/tilt systems
Quadrature encoding can also double or quadruple the resolution, depending on how the software interprets signal edges (rising/falling). For example, a 600 PPR encoder can yield 2400 detectable positions per turn when using 4× decoding.
Why It’s Important to Understand How It Works
If you’re an engineer, a robotics hobbyist, or a product designer, understanding how rotary encoders work isn’t just academic — it’s practical. Misunderstanding signal phasing, resolution, or wiring can lead to incorrect readings, noisy behavior, or even damage to components.
In this article, I’ll guide you through the different types of encoders, how their signals work, how to connect them properly, and how to choose the right one for your project.
H2: What Are the Main Types of Rotary Encoders?
Rotary encoders come in two main categories: incremental and absolute. Both serve the same core function — converting rotation into electrical signals — but they differ in how they deliver that information.
Incremental encoders generate a stream of pulses as the shaft rotates. These pulses count steps but don’t give a specific position unless tracked from a known starting point. They’re commonly used for speed or relative position feedback.
Absolute encoders, on the other hand, output a unique binary (or Gray code) value for each shaft position. Even if power is lost, the encoder remembers its exact location. These are ideal for precision systems where position data must be retained at all times.
Another common comparison people make — especially in hobby electronics — is between rotary encoders and potentiometers. Here’s a side-by-side breakdown to show why rotary encoders are often preferred in modern digital systems:
How to Choose the Right Rotary Encoder (Step-by-Step)
With so many options available, picking the right rotary encoder can feel overwhelming. But if you follow a structured approach — like I do when speccing hardware for a new project — you’ll avoid headaches and get exactly what your system needs. Here’s how to break it down step by step:
Step 1: Define Your Use Case
Start by identifying what the encoder will actually do in your application. Are you trying to:
Measure position (e.g., robotic arm, CNC axis)? → Consider absolute encoders.
Track rotational speed or relative movement (e.g., motor shaft, wheel rotation)? → Go with incremental encoders.
Understanding the task will immediately narrow your options.
Step 2: Choose the Type — Incremental or Absolute
Incremental Encoders output A/B (and sometimes Z) channel pulses. They’re great for counting rotations or monitoring speed — but lose position after a power cycle unless homed again.
Absolute Encoders provide a unique digital value for each shaft angle. Even after a reboot, the system knows exactly where it left off — ideal for safety-critical or high-precision systems.
Tip: If your system can’t afford to “guess” its position after power loss, always go with an absolute encoder.
Step 3: Decide on Resolution (PPR or CPR)
PPR (Pulses Per Revolution) — used in incremental encoders
CPR (Counts Per Revolution) — often used interchangeably, but can also refer to decoded output
Higher resolution = more detailed position/speed data. For example:
100 PPR = basic tasks like knob control or motor speed
1000+ PPR = precise motion control (CNC, robotics)
But remember: higher resolution also means more CPU processing and more signal noise sensitivity.
Step 4: Check Compatibility with Your Controller
Make sure the encoder’s electrical specs match your system:
Voltage: 3.3V, 5V, or 24V logic?
Signal Type: Open collector, push-pull, line driver?
Interface: Are you using digital I/O, interrupts, or SPI/I2C for reading?
Mismatched logic levels or signal types can damage your microcontroller or produce unreliable readings.
Step 5: Choose the Right Mounting & Shaft Style
Encoders come with various shaft and housing designs. Choose one that fits your mechanical setup:
Knurled Shaft — for press-fit knobs
D-Shaft — flat side prevents slippage
Hollow Shaft — slides over an existing axle
Servo Mount or Flange Mount — for secure, fixed installations
Measure your existing motor or panel before ordering!
Step 6: Consider the Environment
Will the encoder operate in a dusty workshop? Near strong magnetic fields? Outdoors?
Go for magnetic encoders if dust, oil, or debris are common.Check for IP ratings (like IP65) for water and dust resistance.
In noisy electrical environments, choose differential (line driver) outputs to reduce interference.
Choosing the right encoder isn’t just about specs — it’s about reliability in the real world. I’ve seen “over-specced” encoders fail in dusty factories and “cheap” ones work flawlessly in hobby robots. Always match the component to the conditions.
In the next section, I’ll walk you through how to wire it up correctly and avoid the most common connection mistakes.
The post How Rotary Encoder Works: Understanding Types, Signals, and Applications appeared first on Moss and Fog.