ComArduino2.py

# 19 July 2014

# in case any of this upsets Python purists it has been converted from an equivalent JRuby program

# this is designed to work with ... ArduinoPC2.ino ...

# the purpose of this program and the associated Arduino program is to demonstrate a system for sending 
#   and receiving data between a PC and an Arduino.

# The key functions are:
#    sendToArduino(str) which sends the given string to the Arduino. The string may 
#                       contain characters with any of the values 0 to 255
#
#    recvFromArduino()  which returns an array. 
#                         The first element contains the number of bytes that the Arduino said it included in
#                             message. This can be used to check that the full message was received.
#                         The second element contains the message as a string


# the overall process followed by the demo program is as follows
#   open the serial connection to the Arduino - which causes the Arduino to reset
#   wait for a message from the Arduino to give it time to reset
#   loop through a series of test messages
#      send a message and display it on the PC screen
#      wait for a reply and display it on the PC

# to facilitate debugging the Arduino code this program interprets any message from the Arduino
#    with the message length set to 0 as a debug message which is displayed on the PC screen

# the message to be sent to the Arduino starts with < and ends with >
#    the message content comprises a string, an integer and a float
#    the numbers are sent as their ascii equivalents
#    for example <LED1,200,0.2>
#    this means set the flash interval for LED1 to 200 millisecs
#      and move the servo to 20% of its range

# receiving a message from the Arduino involves
#    waiting until the startMarker is detected
#    saving all subsequent bytes until the end marker is detected

# NOTES
#       this program does not include any timeouts to deal with delays in communication
#
#       for simplicity the program does NOT search for the comm port - the user must modify the
#         code to include the correct reference.
#         search for the lines 
#               serPort = "/dev/ttyS80"
#               baudRate = 9600
#               ser = serial.Serial(serPort, baudRate)
#

import logging
  
#=====================================

#  Function Definitions

#=====================================

def sendToArduino(sendStr):
  ser.write(sendStr)


#======================================

def recvFromArduino():
  global startMarker, endMarker
  
  ck = ""
  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 = ser.read()
  
  # save data until the end marker is found
  while ord(x) != endMarker:
    if ord(x) != startMarker:
      ck = ck + (x.decode())
      byteCount += 1
    x = ser.read()
  
  return(ck)


#============================

def waitForArduino():

   # wait until the Arduino sends 'Arduino Ready' - allows time for Arduino reset
   # it also ensures that any bytes left over from a previous message are discarded
   
    global startMarker, endMarker
    
    msg = ""
    while msg.find("Arduino is ready") == -1:

      while ser.inWaiting() == 0:
        pass
        
      msg = recvFromArduino()

      print(msg)
      print
      
#======================================

def runTest(td):
  numLoops = len(td)
  waitingForReply = False

  n = 0
  while n < numLoops:

    teststr = td[n]

    if waitingForReply == False:
      sendToArduino(teststr.encode('utf-8'))
      #logging.info("Sent from PC -- LOOP NUM " + str(n) + " TEST STR " + teststr)
      waitingForReply = True

    if waitingForReply == True:

      while ser.inWaiting() == 0:
        pass
        
      dataRecvd = recvFromArduino()
      #logging.info("Reply Received  " + dataRecvd)
      n += 1
      waitingForReply = False

      #logging.info("===========")

    #time.sleep(5)


#======================================

# THE DEMO PROGRAM STARTS HERE

#======================================

import serial
import time

print
print

# NOTE the user must ensure that the serial port and baudrate are correct
serPort = "/dev/ttyUSB0"
#serPort = "COM4"
baudRate = 115200
ser = serial.Serial(serPort, baudRate)
print("Serial port " + serPort + " opened  Baudrate " + str(baudRate))


startMarker = 60
endMarker = 62


if __name__ == '__main__':
  print("waiting for arduino.")
  waitForArduino()
  testData = []
  testData.append("<LED1,200,0.2>")
  testData.append("<LED1,800,0.7>")
  testData.append("<LED2,800,0.5>")
  testData.append("<LED2,200,0.2>")
  testData.append("<LED1,200,0.7>")

  runTest(testData)


  ser.close