python to arduino serial read write

Question

I m trying to  ping pong  info back and forth between some python code and arduino code  I want to send two setpoints to the arduino code periodically  for instance on the minute   read them on arduino  amp  update variables then send status info from arduino back to python periodically  such as on the  30 second    Eventually python will be sending and pulling info from a mySQL db  later dev    Right now I can t get the info to bounce back and forth reliably   I haven t found anything close to this in the searches and everything I ve tried to modify isn t working   Closest I have is this  and it doesn t actually switch back and forth between send and receive    Python     usr bin python import serial import syslog import time   The following line is for serial over GPIO port     dev ttyS0    ard   serial Serial port 9600 timeout 5   i   0  while  i  lt  4         Serial write section      setTempCar1   63     setTempCar2   37     ard flush       setTemp1   str setTempCar1      setTemp2   str setTempCar2      print   Python value sent         print  setTemp1      ard write setTemp1      time sleep 4         Serial read section     msg   ard readline       print   Message from arduino         print  msg      i   i   1 else      print  Exiting  exit     Arduino      Serial test script  int setPoint   55  String readString   void setup        Serial begin 9600       initialize serial communications at 9600 bps     void loop       while  Serial available            serial read section   while  Serial available            if  Serial available    gt 0              char c   Serial read       gets one byte from serial buffer       readString    c    makes the string readString              if  readString length    gt 0          Serial print  Arduino received            Serial println readString     see what was received        delay 500         serial write section    char ard sends    1     Serial print  Arduino sends        Serial println ard sends     Serial print   n      Serial flush        All I end up getting is the same values repeated  not what was actually sent  not sure if its a string or byte issue  and nothing back to the python script   Any help or ideas are greatly appreciated   Thanks   EDIT  Modified code to what I m currently running as suggested below   Arduino is receiving fine and serial communication verified by minicom   But python script still prints a blank line after  Message from arduino

User · Answer

First you have to install a module call Serial. To do that go to the folder call Scripts which is located in python installed folder. If you are using Python 3 version it's normally located in location below,

C:\Python34\Scripts

Once you open that folder right click on that folder with shift key. Then click on 'open command window here'. After that cmd will pop up. Write the below code in that cmd window,

pip install PySerial

and press enter.after that PySerial module will be installed. Remember to install the module u must have an INTERNET connection.

after successfully installed the module open python IDLE and write down the bellow code and run it.

import serial
# "COM11" is the port that your Arduino board is connected.set it to port that your are using        
ser = serial.Serial("COM11", 9600)
while True:
    cc=str(ser.readline())
    print(cc[2:][:-5])

User · Answer

You shouldn t be closing the serial port in Python between writing and reading  There is a chance that the port is still closed when the Arduino responds  in which case the data will be lost   while running          Serial write section     setTempCar1   63     setTempCar2   37     setTemp1   str setTempCar1      setTemp2   str setTempCar2      print   Python value sent         print  setTemp1      ard write setTemp1      time sleep 6    with the port open  the response will be buffered                      so wait a bit longer for response here        Serial read section     msg   ard read ard inWaiting      read everything in the input buffer     print   Message from arduino         print  msg    The Python Serial read function only returns a single byte by default  so you need to either call it in a loop or wait for the data to be transmitted and then read the whole buffer   On the Arduino side  you should consider what happens in your loop function when no data is available    void loop          serial read section   while  Serial available       this will be skipped if no data present  leading to                                 the code sitting in the delay function below         delay 30      delay to allow buffer to fill      if  Serial available    gt 0              char c   Serial read       gets one byte from serial buffer       readString    c    makes the string readString             Instead  wait at the start of the loop function until data arrives   void loop       while   Serial available          wait for data to arrive      serial read section   while  Serial available               continue as before   EDIT 2  Here s what I get when interfacing with your Arduino app from Python    gt  gt  gt  import serial  gt  gt  gt  s   serial Serial   dev tty usbmodem1411   9600  timeout 5   gt  gt  gt  s write  2   1  gt  gt  gt  s readline    Arduino received  2 r n    So that seems to be working fine   In testing your Python script  it seems the problem is that the Arduino resets when you open the serial port  at least my Uno does   so you need to wait a few seconds for it to start up  You are also only reading a single line for the response  so I ve fixed that in the code below also      usr bin python import serial import syslog import time   The following line is for serial over GPIO port     dev tty usbmodem1411    note I m using Mac OS-X   ard   serial Serial port 9600 timeout 5  time sleep 2    wait for Arduino  i   0  while  i  lt  4         Serial write section      setTempCar1   63     setTempCar2   37     ard flush       setTemp1   str setTempCar1      setTemp2   str setTempCar2      print   Python value sent         print  setTemp1      ard write setTemp1      time sleep 1    I shortened this to match the new value in your Arduino code        Serial read section     msg   ard read ard inWaiting      read all characters in buffer     print   Message from arduino         print  msg      i   i   1 else      print  Exiting  exit     Here s the output of the above now     python ardser py Python value sent  63 Message from arduino  Arduino received  63 Arduino sends  1   Python value sent  63 Message from arduino  Arduino received  63 Arduino sends  1   Python value sent  63 Message from arduino  Arduino received  63 Arduino sends  1   Python value sent  63 Message from arduino  Arduino received  63 Arduino sends  1   Exiting

User · Answer

I found it is better to use the command Serial readString   to replace the Serial read   to obtain the continuous I O for Arduino

[python] python to arduino serial read & write

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