---
title: Meet the Quadrature Encoder
summary: Learn what the A and B channels are and why their phase offset lets you count motion.
chapter: Reading Encoder Signals
order: 1
tags:
  - encoders
  - motors
  - feedback
estimated_minutes: 8
---

# Meet the Quadrature Encoder

A quadrature encoder gives you two square-wave signals, usually called `A` and `B`.

Those signals toggle as the shaft turns. The important detail is that they do not toggle at the same time. One channel leads the other by a quarter of a cycle, which is where the name quadrature comes from.

That phase offset gives you two useful facts:

1. You can count edges to measure motion.
2. You can compare which signal leads to determine direction.

## What you should observe

- Slow rotation produces clean transitions you can inspect with a logic analyzer.
- Reversing the shaft swaps which channel leads.
- More pulses per revolution means finer position measurement.

## Checkpoint

Capture both channels while rotating the shaft by hand and confirm that one channel leads the other.