quadrature-encoder-course/lessons/01-reading-encoder-signals/02-counting-direction-and-steps/counting-direction-and-steps.md

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