pyKY040

High-level Python module for the KY040 rotary encoder and switch on Raspberry Pi and similar boards that use RPi.GPIO

Features

• Increment callback
• Decrement callback
• Change callback (increment or decrement)
• Switch press callback

Options

• Scale mode (internal counter is bound between X and Y, and is given as argument in the callback functions)
• Looped scale mode (from X to Y, then X again)
• Custom scale step
• GPIO polling (easier) or as a device (sturdier)

Installation

pip install pyky040

Basic

# Import the module
from pyky040 import pyky040

# Define your callback
def my_callback(scale_position):
    print('Hello world! The scale position is {}'.format(scale_position))

# Init the encoder pins
my_encoder = pyky040.Encoder(CLK=17, DT=18, SW=26)

# Or the encoder as a device (must be installed on the system beforehand!)
# my_encoder = pyky040.Encoder(device='/dev/input/event0')

# Setup the options and callbacks (see documentation)
my_encoder.setup(scale_min=0, scale_max=100, step=1, chg_callback=my_callback)

# Launch the listener
my_encoder.watch()

# Mess with the encoder...
# > Hello world! The scale position is 1
# > Hello world! The scale position is 2
# > Hello world! The scale position is 3
# > Hello world! The scale position is 2
# > Hello world! The scale position is 1

In a thread

As the watch() method runs an infinite polling loop, you might want to run it in a thread if you don't want to block the rest of your script, or if you have multiple encoders to handle.

# Import the module and threading
from pyky040 import pyky040
import threading

# Define your callback
def my_callback(scale_position):
    print('Hello world! The scale position is {}'.format(scale_position))

# Init the encoder pins
my_encoder = pyky040.Encoder(CLK=17, DT=18, SW=26)

# Or the encoder as a device (must be installed on the system beforehand!)
# my_encoder = pyky040.Encoder(device='/dev/input/event0')

# Setup the options and callbacks (see documentation)
my_encoder.setup(scale_min=0, scale_max=100, step=1, chg_callback=my_callback)

# Create the thread
my_thread = threading.Thread(target=my_encoder.watch)

# Launch the thread
my_thread.start()

# Do other stuff
print('Other stuff...')
while True:
    print('Looped stuff...')
    sleep(1000)
# ... this is also where you can setup other encoders!

# Mess with the encoder...
# > Other stuff...
# > Looped stuff...
# > Hello world! The scale position is 1
# > Hello world! The scale position is 2
# > Hello world! The scale position is 3
# > Looped stuff...
# > Hello world! The scale position is 2

Note: The interruption of the module when running in threads is not yet handled, you might have to kill it by yourself 🔪

Documentation

Encoder(CLK=x, DT=y, SW=z)

Initializes the module with the specified encoder pins.

• Options
  • polling_interval Specify the pins polling interval in ms (default 1ms)

Encoder(device='...')

⚠️ Linux only

Initializes the module with the specified encoder device. Read more

Requirement: pip install pyky040[device]

Encoder.setup()

Setup the behavior of the module. All of the following keyword arguments are optional.

• Callbacks

  • inc_callback (function) When the encoder is incremented (clockwise). Scale position as first argument.
  • dec_callback (function) When the encoder is decremented. Scale position as first argument.
  • chg_callback (function) When the encoder is either incremented or decremented. Scale position as first argument.
  • sw_callback (function) When the encoder switch is pressed

• Scale mode

  • scale_min (int/float) Scale minimum
  • scale_max (int/float) Scale maximum
  • loop (boolean) Loop mode (defaults to False)
  • step (int/float) Scale step when incrementing or decrementing

• Options

  • sw_debounce_time (int/float) Switch debounce time in ms (allow only one interrupt per X ms, dismiss others)

Note: better keep using ints and not floats for more precise results.

Encoder.watch()

Starts the listener. The pins polling interval is 1ms by default and can be customized (see Encoder()).

Should I use the GPIO polling or the device overlay?

The Raspberry Pi firmware allows the encoder to be set up as a device with the rotary-encoder overlay. It trades the promise to catch every encoder tick for the ease of use (because it needs to be installed on the host beforeheand, with root privileges).

Approach	Plug & Play	Needs prior installation	Catches every tick
GPIO polling	Yes	No	No
Device overlay	No	Yes	Yes

How to install the encoder as a device?

Only tested on Raspbian Buster at this time.

# Copy this line in `/boot/config.txt` and reboot
# (replacing {CLK_PIN} and {DT_PIN} by their real values)
dtoverlay=rotary-encoder,pin_a={CLK_PIN},pin_b={DT_PIN},relative_axis=1,steps-per-period=2

TROUBLESHOOTING

Erratic behavior

It is known that some pins combinations introduce erratic behavior (interferences?). The library has been tested successfully using the following combinations (BCM numbering).

CLK	DT	SW	Pi	Raspbian
26	4	21	3B (1.2)	Buster

Feel free to edit the README to provide your working combinations!

If you are still experiencing issues, you might want to try to set up the encoder as a device instead.

CHANGELOG

0.1.4

• Added device mode
• Added tests

0.1.3

• Fixed latest_switch_call not defined before the loop

0.1.2

• Changed __init_ args to kwargs for better readability and ease of use Encoder(CLK=x, DT=y, SW=z)
• Added customizable debounce time (in ms) for the switch setup(..., sw_debounce_time=300)
• Added customizable polling interval (in ms) Encoder(..., polling_interval=1)