---
title: Counting Direction and Steps
summary: Decode edges from the A and B channels to recover step count and direction.
chapter: Reading Encoder Signals
order: 2
tags:
  - decoding
  - interrupts
  - firmware
estimated_minutes: 10
---

# Counting Direction and Steps

Once you can read the A and B channels, the next job is decoding.

The most common approach is:

- trigger on an edge
- read both channels
- use a lookup table or state machine to update the count

If your decoder sees illegal state jumps, you are probably dropping edges or reading a noisy signal.

## Practical notes

- Start with low shaft speed.
- Add debounce or filtering only if the hardware needs it.
- Test forward and reverse explicitly.

## Checkpoint

Write firmware that increments a counter when the shaft turns forward and decrements when it turns backward.