Rotary encoder / Wheel encoder

Why ?

Convert a binary information in a speed and with direction knowledged

Requirement

1 GPIO (Raspberry pi)
2 endstop sensors
1 spring
3 nails
6 screws (2 by endstop and 2 for spring)

Print parts

Wheel
Diameter : 50mm
4 holes so 4 states 0 and 4 states 1 for a complet revolution

Main part
To fix spring, wheel and sensors

Holder
To fix main part and spring

What we want to get on the raspberry GPIO

number of change of state 0 -> 1 -> 0 -> 1 ... by rotation : 8

Config

You can change settings:

• pin numbers used by 2 endstop sensors (23 & 24 by default)
• wheel diameter (5cm by default)
• number of holes in wheel (4 by default)

Code part

Create a file "nb_turn_second.py"
Add permissions (chmod +x nb_turn_second.py"
Insert this script inside and run it with "./nb_turn_second.py"

#!/usr/bin/pythonimport RPi.GPIO as GPIOimport timeprint "starting..."pin_id = 23pin2_id = 24wheel_diameter = 5 #cmnb_holes_in_wheel = 4nb_states_by_rotation = float(nb_holes_in_wheel * 2)pi = 3.14wheel_perimeter = pi * wheel_diameterGPIO.setmode(GPIO.BCM)GPIO.setup(pin_id, GPIO.IN, pull_up_down=GPIO.PUD_UP)GPIO.setup(pin2_id, GPIO.IN, pull_up_down=GPIO.PUD_UP)last_state = 0nb_states = 0previous_second = 0previous_nb_states = 0is_direction_A = Truetry:  while True:    input_state = GPIO.input(pin_id)    input2_state = GPIO.input(pin2_id)    if input_state != last_state:      if input_state == input2_state:        nb_states -= 1        if is_direction_A:          is_direction_A = False          print('direction changed')      else:        nb_states += 1        if not is_direction_A:          is_direction_A = True          print('direction changed')      last_state = input_state    current_second = time.strftime('%S')    if current_second != previous_second:      if nb_states != previous_nb_states:        previous_nb_states = nb_states        nb_rotation = 0        if previous_nb_states != 0:          nb_rotation = previous_nb_states / nb_states_by_rotation        speed_second = nb_rotation * wheel_perimeter        print ('nb rotation: ' + str(nb_rotation) + '; speed: ' + str(speed_second) + " cm/s")      previous_second = current_second      nb_states = 0    time.sleep(0.01)except:  GPIO.cleanup()

This script will display every second the new speed only if the speed changed

output example

starting...nb rotation: 0.875; speed: 13.7375 cm/snb rotation: 0.75; speed: 11.775 cm/snb rotation: 1.0; speed: 15.7 cm/sdirection changednb rotation: 1.25; speed: 19.625 cm/snb rotation: -0.625; speed: -9.8125 cm/snb rotation: -0.75; speed: -11.775 cm/snb rotation: -0.25; speed: -3.925 cm/snb rotation: 0; speed: 0.0 cm/s