MicroPython Rotary Encoder Driver

A MicroPython driver to read a rotary encoder. Works with Pyboard, ESP8266, and ESP32 development boards. This is a robust implementation providing effective debouncing of encoder contacts. It uses two GPIO pins configured to trigger interrupts, following Ben Buxton's implementation:

• http://www.buxtronix.net/2011/10/rotary-encoders-done-properly.html
• https://github.com/buxtronix/arduino/tree/master/libraries/Rotary

Key Implementation Features

Interrupt based

Whenever encoder pins DT and CLK change value a hardware interrupt is generated. This interrupt causes a python-based interrupt service routine (ISR) to run. The ISR interrupts normal code execution to process state changes in the encoder pins.

Transition state machine

A gray code based transition state table is used to process the DT and CLK changes. The use of the state table leads to accurate encoder counts and effective switch debouncing. Credit: Ben Buxton

File Installation

Two files are needed to use this module

• platform-independent file rotary.py - a core file for all development boards
• platform-specific file:
  • rotary_irq_esp.py Platform-specific code for ESP8266 and ESP32 development boards
  • rotary_irq_pyb.py Platform-specific code for Pyboard development boards

Copying files to development boards

Copy files to the internal MicroPython filesystem using a utility such as ampy or rshell Ampy example below for Pyboards. Note: -d1 option is often needed for ESP8266 boards

ampy -pCOMx put rotary.py
ampy -pCOMx put rotary_irq_pyb.py

Class RotaryIRQ

Constructor

   RotaryIRQ(
       pin_num_clk, 
       pin_num_dt, 
       min_val=0, 
       max_val=10, 
       reverse=False, 
       range_mode=RotaryIRQ.RANGE_UNBOUNDED,
       pull_up=False,
       half_step=False)

Methods

value() Return the encoder value

set(value=None, min_val=None, max_val=None, reverse=None, range_mode=None) Set encoder value and internal configuration parameters. See constructor for argument descriptions. None indicates no change to the configuration parameter

Examples:

• set(min_val=0, max_val=59) change encoder bounds - useful to set minutes on a clock display
• set(value=6) change encoder value to 6. calling value() will now return 6

reset() set encoder value to min_val. Redundant with the addition of the set() method. Retained for backwards compatibility)

add_listener(function) add a callback function that will be called on each change of encoder count

remove_listener(function) remove a previously added callback function

close() deactivate microcontroller pins used to read encoder

Note: None of the arguments are checked for configuration errors.

Example

• CLK pin attached to GPIO12
• DT pin attached to GPIO13
• GND pin attached to GND
• + pin attached to 3.3V
• Range mode = RotaryIRQ.RANGE_WRAP
• Range 0...5

import time
from rotary_irq_esp import RotaryIRQ

r = RotaryIRQ(pin_num_clk=12, 
              pin_num_dt=13, 
              min_val=0, 
              max_val=5, 
              reverse=False, 
              range_mode=RotaryIRQ.RANGE_WRAP)
              
val_old = r.value()
while True:
    val_new = r.value()
    
    if val_old != val_new:
        val_old = val_new
        print('result =', val_new)
        
    time.sleep_ms(50)

• For clockwise turning the encoder will count 0,1,2,3,4,5,0,1 ...
• For counter-clockwise turning the encoder will count 0,5,4,3,2,1,0,5,4 ....

Tested With:

Development Boards

• Pyboard D
• PYBv1.1
• TinyPico
• Lolin D32 (ESP32)
• Lolin D32 Pro (ESP32 with 4MB PSRAM)
• Adafruit Feather Huzzah ESP8266
• Adafruit Feather Huzzah ESP32

Rotary Encoders

• KY-040 rotary encoder

MicroPython versions

• MicroPython v1.12
• MicroPython v1.13
• MicroPython v1.14

Rotary Encoder Wiring

Recommended ESP8266 input pins

This Rotary module requires pins that support interrupts. The following ESP8266 GPIO pins are recommended for this rotary encoder module

• GPIO4
• GPIO5
• GPIO12
• GPIO13
• GPIO14

The following ESP8266 GPIO pins should be used with caution. There is a risk that the state of the CLK and DT signals can affect the boot sequence. When possible, use other GPIO pins.

• GPIO0 - used to detect boot-mode. Bootloader runs when pin is low during powerup.
• GPIO2 - used to detect boot-mode. Attached to pull-up resistor.
• GPIO15 - used to detect boot-mode. Attached to pull-down resistor.

One pin does not support interrupts.

• GPIO16 - does not support interrupts.

Recommended ESP32 input pins

This Rotary module requires pins that support interrupts. All ESP32 GPIO pins support interrupts.

The following ESP32 GPIO strapping pins should be used with caution. There is a risk that the state of the CLK and DT signals can affect the boot sequence. When possible, use other GPIO pins.

• GPIO0 - used to detect boot-mode. Bootloader runs when pin is low during powerup. Internal pull-up resistor.
• GPIO2 - used to enter serial bootloader. Internal pull-down resistor.
• GPIO4 - technical reference indicates this is a strapping pin, but usage is not described. Internal pull-down resistor.
• GPIO5 - used to configure SDIO Slave. Internal pull-up resistor.
• GPIO12 - used to select flash voltage. Internal pull-down resistor.
• GPIO15 - used to configure silencing of boot messages. Internal pull-up resistor.

Examples

MicroPython example code is contained in the Examples folder
simple example
uasyncio example
uasyncio with classes example

Oscilloscope Captures

CLK and DT transitions captured on an oscilloscope. CLK = Yellow. DT = Blue

One clockwise step

One counter-clockwise step

Board Hall of Fame

Testing with Pyboard D, Pyboard v1.1, and TinyPico development boards

Acknowlegements

This MicroPython implementation is an adaptation of Ben Buxton's C++ work:

• https://github.com/buxtronix/arduino/tree/master/libraries/Rotary

Other implementation ideas and techniques taken from:

• https://github.com/SpotlightKid/micropython-stm-lib/tree/master/encoder
• https://www.youtube.com/watch?v=BJHftzjNjkw
• https://github.com/dhylands/python_lcd

Future Ambitions

• Raspberry Pi Pico support
• argument error checking