serial communication with pc using pySerial

Projects Programming
1

I am working on a bigger project but I narrowed my problem down to this.
Its the basic of the basics but it does not work for me, I guess it has a simple
solution. Please help.

Arduino code:

void setup() {
  Serial.begin(9600);
}

void loop() {
  if(Serial.available())
  {  
      String msg = String(Serial.read());
      delay(500);
      Serial.println(msg);
      
  }
}

python code:

import serial

SERIAL = serial.Serial('COM4', baudrate=9600, timeout=1)

SERIAL.write('e'.encode())
print(SERIAL.read())

the python output which I get is this: b'' (basically nothing)

2

schmenton:
but it does not work for me,

[...]

the python output which I get is this: b'' (basically nothing)

What should it be doing?

Maybe this Simple Python - Arduino demo will help.

...R

3

It would be much more reliable to interface Python with your Arduino using the compatible libraries: pySerialTransfer and SerialTransfer.h.

pySerialTransfer is pip-installable and cross-platform compatible. SerialTransfer.h runs on the Arduino platform and can be installed through the Arduino IDE's Libraries Manager.

Both of these libraries have highly efficient and robust packetizing/parsing algorithms with easy to use APIs.

Example Python Script:

import time
from pySerialTransfer import pySerialTransfer as txfer


if __name__ == '__main__':
    try:
        link = txfer.SerialTransfer('COM17')
        
        link.open()
        time.sleep(2) # allow some time for the Arduino to completely reset
        
        while True:
            send_size = 0
            
            ###################################################################
            # Send a list
            ###################################################################
            list_ = [1, 3]
            list_size = link.tx_obj(list_)
            send_size += list_size
            
            ###################################################################
            # Send a string
            ###################################################################
            str_ = 'hello'
            str_size = link.tx_obj(str_, send_size) - send_size
            send_size += str_size
            
            ###################################################################
            # Send a float
            ###################################################################
            float_ = 5.234
            float_size = link.tx_obj(float_, send_size) - send_size
            send_size += float_size
            
            ###################################################################
            # Transmit all the data to send in a single packet
            ###################################################################
            link.send(send_size)
            
            ###################################################################
            # Wait for a response and report any errors while receiving packets
            ###################################################################
            while not link.available():
                if link.status < 0:
                    if link.status == -1:
                        print('ERROR: CRC_ERROR')
                    elif link.status == -2:
                        print('ERROR: PAYLOAD_ERROR')
                    elif link.status == -3:
                        print('ERROR: STOP_BYTE_ERROR')
            
            ###################################################################
            # Parse response list
            ###################################################################
            rec_list_  = link.rx_obj(obj_type=type(list_),
                                     obj_byte_size=list_size,
                                     list_format='i')
            
            ###################################################################
            # Parse response string
            ###################################################################
            rec_str_   = link.rx_obj(obj_type=type(str_),
                                     obj_byte_size=str_size,
                                     start_pos=list_size)
            
            ###################################################################
            # Parse response float
            ###################################################################
            rec_float_ = link.rx_obj(obj_type=type(float_),
                                     obj_byte_size=float_size,
                                     start_pos=(list_size + str_size))
            
            ###################################################################
            # Display the received data
            ###################################################################
            print('SENT: {} {} {}'.format(list_, str_, float_))
            print('RCVD: {} {} {}'.format(rec_list_, rec_str_, rec_float_))
            print(' ')
    
    except KeyboardInterrupt:
        link.close()
    
    except:
        import traceback
        traceback.print_exc()
        
        link.close()

Example Arduino Sketch:

#include "SerialTransfer.h"


SerialTransfer myTransfer;


void setup()
{
  Serial.begin(115200);
  myTransfer.begin(Serial);
}


void loop()
{
  if(myTransfer.available())
  {
    // send all received data back to Python
    for(uint16_t i=0; i < myTransfer.bytesRead; i++)
      myTransfer.txBuff[i] = myTransfer.rxBuff[i];
    
    myTransfer.sendData(myTransfer.bytesRead);
  }
}

On the Arduino side, you can use myTransfer.txObj() and myTransfer.rxObj() to copy values to the library's RX buffer and parse multi-byte variables out of the library's TX buffer.

For theory behind robust serial communication, check out the tutorials Serial Input Basics and Serial Input Advanced.