Python to Arduino Communication Issues whilst using an LN-101 USB Serial Downloader

Official Hardware Mega Mega 2560
1

Good day! I'm currently working on a project which involves writing to and reading from a Dynamixel XL-430W-250T via Python. My current setup involves a Dynamixel Motor Shield which I've connected to my PC via an Arduino Uno and USB 2.0. I've supplemented the connection with an LN-101 Serial USB Downloader, as Dynamixels notoriously clog the serial ports of the USB 2.0, which results in garbage being output to the serial monitor.

My python script encodes a string and writes it to the Arduino via the LN-101, which it then reads and writes back to the computer so as to "verify" the command. The arduino script utilizes the Dynamixel Shield library.

Python script:

import os   
import time    
import re   
import serial   
import sys
import msvcrt

USB2 = serial.Serial(port = 'COM12', timeout=None)   
USB2.baudrate = 115200   
USB2.bytesize = serial.EIGHTBITS    
USB2.parity = serial.PARITY_NONE   
USB2.stopbits = serial.STOPBITS_ONE  

LN101 = serial.Serial(port = 'COM32', timeout=None)   
LN101.baudrate = 115200  
LN101.bytesize = serial.EIGHTBITS   
LN101.parity = serial.PARITY_NONE  
LN101.stopbits = serial.STOPBITS_ONE 

while check == False:
        toard = ("{}\0".format(string))
        LN101.reset_output_buffer()
        LN101.write(str.encode(toard)) 
        toard = toard.rstrip("\0")
        time.sleep(2)
        if LN101.in_waiting > 0:
            comcheck = str(LN101.readline().decode('utf-8')) 
            comcheck = comcheck.rstrip("\n")

Arduino code:

#include <DynamixelShield.h>

#if defined(ARDUINO_AVR_UNO) || defined(ARDUINO_AVR_MEGA2560)
  #include <SoftwareSerial.h>
  SoftwareSerial soft_serial(7, 8); // DYNAMIXELShield UART RX/TX
  #define DEBUG_SERIAL soft_serial
#elif defined(ARDUINO_SAM_DUE) || defined(ARDUINO_SAM_ZERO)
  #define DEBUG_SERIAL SerialUSB    
#else
  #define DEBUG_SERIAL Serial
#endif

DynamixelShield dxl;  

const uint8_t DXL_ID = 1; 
const float DXL_PROTOCOL_VERSION = 2.0, dtime = 100; 
const int maxVelval = 330; 
unsigned long tstart;
int vel, goalVelval, sep1, sep2, c=0; 
long int pos_i, pos_c, pos_f, desrotval, zero;
float pos, dpos, tpos, pos_i_rel, veldegmsec, delaymsec;  
String Sdir, Svel, Spos, Spos2, Fpos, SZero, toard, fromard, comcheck, check, btoard, tora;

using namespace ControlTableItem;

void setup() {
  DEBUG_SERIAL.begin(115200); 
  Serial.begin(115200); 
  dxl.begin(57600); 
  dxl.setPortProtocolVersion(DXL_PROTOCOL_VERSION);
  dxl.ping(DXL_ID); 
  dxl.torqueOff(DXL_ID); 
  dxl.setOperatingMode(DXL_ID, OP_EXTENDED_POSITION); 
  dxl.torqueOn(DXL_ID); 
}

void loop() {
  comcheck = "False";
  tora = "Recieved\n";
  fromard = "";
  toard = "";
  while (comcheck == "False") {
    while (DEBUG_SERIAL.available() == 0) {}    
    toard = DEBUG_SERIAL.readStringUntil('\0');  
    toard.trim(); //
    btoard = toard;
    fromard = toard += "\n";
    DEBUG_SERIAL.write(fromard.c_str());
    delay(100);
}

The code works just fine when I'm utilizing an Uno; however, if I try to switch the board to a Mega, the serial communication over the LN-101 doesn't seem to work (from what I can tell, the arduino never reads the initial command written by the computer).

Troubleshooting thus far:

  • The baudrate is the same for both the uno and mega
  • Everything is mounted correctly on the Arduino
  • The board, LN-101 and USB 2.0 seem to be working just fine
  • The arduino seems to write to the com port just fine; it just never receives anything from python for whatever reason

Could I please get some help in resolving this?

2

This topic was automatically closed 180 days after the last reply. New replies are no longer allowed.