Wheel speed ========== 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/python

import RPi.GPIO as GPIO import time

print "starting..."

pin_id = 23 pin2_id = 24

wheel_diameter = 5 #cm nb_holes_in_wheel = 4

nb_states_by_rotation = float(nb_holes_in_wheel * 2) pi = 3.14 wheel_perimeter = pi * wheel_diameter

GPIO.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 = 0 nb_states = 0

previous_second = 0 previous_nb_states = 0 is_direction_A = True

try: 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/s nb rotation: 0.75; speed: 11.775 cm/s nb rotation: 1.0; speed: 15.7 cm/s direction changed nb rotation: 1.25; speed: 19.625 cm/s nb rotation: -0.625; speed: -9.8125 cm/s nb rotation: -0.75; speed: -11.775 cm/s nb rotation: -0.25; speed: -3.925 cm/s nb rotation: 0; speed: 0.0 cm/s ```