Raspberry Pi communication interfaces.

A project log for DIY hobby servos quadruped robot

Cheap 3D printed 4 legged robot, that almost looks like boston dynamics spot but moves like a newborn.

Miguel Ayuso ParrillaMiguel Ayuso Parrilla 06/21/2020 at 21:410 Comments

This log is going to be about the python communication files, explaining the interfaces used in order to communicate both with the ps3 controller and with the arduino.

Serial Bidirectional Communication on python.

This is written in the file and the code goes as follow:

import serial

class ArduinoSerial: 
    def __init__(self , port):
        #ls -l /dev | grep ACM to identify serial port of the arduino
        self.arduino = serial.Serial(port, 500000, timeout = 1)
        self.arduino.setDTR(False) #force an arduino reset
def serialSend(self, pulse):  
        comando = "<{0}#{1}#{2}#{3}#{4}#{5}#{6}#{7}#{8}#{9}#{10}#{11}>" #Input
        command=comando.format(int(pulse[0]), int(pulse[1]), int(pulse[2]), 
                                   int(pulse[3]), int(pulse[4]), int(pulse[5]), 
                                   int(pulse[6]), int(pulse[7]), int(pulse[8]), 
                                   int(pulse[9]), int(pulse[10]), int(pulse[11]))
        self.arduino.write(bytes(command , encoding='utf8'))

    def serialRecive(self):
            startMarker = 60
            endMarker = 62
            getSerialValue = bytes()
            x = "z" # any value that is not an end- or startMarker
            byteCount = -1 # to allow for the fact that the last increment will be one too many
            # wait for the start character
            while  ord(x) != startMarker: 
                x =
                # save data until the end marker is found
            while ord(x) != endMarker:
                if ord(x) != startMarker:
                    getSerialValue = getSerialValue + x 
                    byteCount += 1
                x =
            loopTime , Xacc , Yacc , roll , pitch  = numpy.fromstring(getSerialValue.decode('ascii', errors='replace'), sep = '#' )  

Connecting PS3 controller to the Raspberry Pi and reading its events.

from evdev import InputDevice, categorize, ecodes
from select import select
import numpy as np

class Joystick:
    def __init__(self , event):
        #python3 /usr/local/lib/python3.8/dist-packages/evdev/ for identify event
        self.gamepad = InputDevice(event)

    def read(self):
        r,w,x = select([self.gamepad.fd], [], [], 0.)
        if r:
            for event in
                if event.type == ecodes.EV_KEY:
                    if event.value == 1:
                        if event.code == 544:#up arrow
                            self.T += 0.05
                        if event.code == 545:#down arrow
                            self.T -= 0.05
                        if event.code == 308:#square
                            if self.compliantMode == True:
                                self.compliantMode = False
                            elif self.compliantMode == False:
                                self.compliantMode = True    
                        print("boton soltado")

                elif event.type == ecodes.EV_ABS:
                    absevent = categorize(event)
                    if ecodes.bytype[absevent.event.type][absevent.event.code] == "ABS_X":  
                    elif ecodes.bytype[absevent.event.type][absevent.event.code] == "ABS_Y":
                    elif ecodes.bytype[absevent.event.type][absevent.event.code] == "ABS_RX":
                    elif ecodes.bytype[absevent.event.type][absevent.event.code] == "ABS_RY":