Rotary encoder / Wheel encoder

thingiverse

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 ```