A state-machine based quadrature decoder, licensed under the MIT license. Support is provided for both full-step (event only after four transitions in the same direction) and half-step (event only after two transitions in the same direction).
Half-step is more aligned with many existing hardware QDEC peripherals, and some other libraries.
For rotary encoders with detents that go through a full four-state transition for each detent, full-step is likely preferable, as only one event will be generated for each "step" of the knob.
The starting point for understanding how this library works is the different state diagrams. There are two distinct state diagrams, one each for half-step and full-step configurations. Each diagram shows states as boxes, with exiting transition lines based on the two new binary values read from the two pins.
Each state includes one invalid state transition. The diagrams
show these using dark-red numbers (the only color in the diagram).
By having these invalid state transitions go to a starting state
(Start and Mid), spurious events are avoided without complex code.
Simple Hack! Because two (or four) state transitions in the same
direction must occur prior to an event being reported, bouncing
of a single pin will simply cause transitions between intermediate
states, and will not cause an event.
For example, if state is bouncing between 0b10 and 0b11, at
most one event will be generated, and only where the initial state
was either CW C, or where the initial state was CCW A
(but only in half-step mode).
The state diagrams can be directly converted into a state transition table. The entire state transition table (including event indication) is 32 bytes (64 if using both full-step and half-step modes).
A single templated class provides two static functions:
Init()to set pin modesUpdate()to read updated pin states, change current state according to the state transition table, and report via the return value if an event occurred.
See the library's samples. The breadboard setup generally used is shown here.
Are you getting clockwise events when turning the encoder counter-clockwise (and vice-versa)? This happens because some encoder signals occur in reverse compared to other encoders. Luckily, the fix is simple. Choose any of the following:
- swap the definitions of ROTARY_PIN_A and ROTARY_PIN_B
- change the order you pass the pins to the QDEC library
- swap the physical wiring to the Arduino pins