# Rotary encoder (KY-040)

<abstract>
This article illustrates how to use the KY-040 Rotary Encode Module on a CM-Panel 
</abstract>

<img src="./KY040.png" width="230px">

The KY-040 rotary ancoder is a very cheap module useful to simulate a potentiometers or to implements an easy to use human interface.

It is available at very low price on Amazon

* <https://www.amazon.it/s?k=ky040>
 
and can be wired to a Raspberry Pi using just 3 GPIO


| KY040 | Pi       |
|-------|----------|
| CLK   | GPIO23   |
| DT    | GPIO24   |
| SW    | GPIO22   |
| +     | 3V3      |
| GND   | GND      |

See the [KY-040 datasheet](https://www.rcscomponents.kiev.ua/datasheets/ky-040-datasheet.pdf) for more details

## Activate the Linux Kernel Driver

Insert these two lines inside the __/boot/config.txt__ file and reboot to activate the Kernel driver

	dtoverlay=rotary-encoder,pin_a=23,pin_b=24,relative_axis=1
	dtoverlay=gpio-key,gpio=22,keycode=28,label="ENTER"

after rebooting two new /dev/input/eventX driver will appear

	ls /dev/input/event*

To do a quickly test install evtest package:

	sudo apt update
	sudo apt install evtest

Then check the rotary movements

	evtest /dev/input/event4

and the key pressing

	evtest /dev/input/event3

## Python example

Here is a simple Python simple example. Install evdev library for Python3 (or python 2):

	sudo apt update
	sudo apt install python3-evdev

Create a file called rotary.py with Python code:

	# -*- encoding: utf-8 -*-
	from __future__ import print_function
	
	import evdev
	import select
	
	devices = [evdev.InputDevice(fn) for fn in evdev.list_devices()]
	devices = {dev.fd: dev for dev in devices}
	
	value = 1
	print("Value: {0}".format(value))
	
	done = False
	while not done:
		r, w, x = select.select(devices, [], [])
		for fd in r:
			for event in devices[fd].read():
				event = evdev.util.categorize(event)
				if isinstance(event, evdev.events.RelEvent):
					value = value + event.event.value
					print("Value: {0}".format(value))
				elif isinstance(event, evdev.events.KeyEvent):
					if event.keycode == "KEY_ENTER" and event.keystate == event.key_up:
						done = True
						break

Launch it by typing:

	python3 rotary.py

<img width="60%" src="https://www.raspberrypi.com/documentation/computers/images/GPIO-Pinout-Diagram-2.png">

## Links

* [KY-040 datasheet](https://www.rcscomponents.kiev.ua/datasheets/ky-040-datasheet.pdf)
* [KY-040 Rotary Encoder with Linux on the Raspberry Pi](https://blog.ploetzli.ch/2018/ky-040-rotary-encoder-linux-raspberry-pi/)
* [Linux Kernel rotary encoder driver doc](https://www.kernel.org/doc/Documentation/input/rotary-encoder.txt)
* <https://github.com/eclipse/paho.mqtt.python>

## MQTT 

This part is still under construction...

	sudo apt update
	sudo apt install python3-paho-mqtt