Tutorial on connecting an Arduino or Microcontroller (AVR ATmega328P,MSP430 ,PIC) with a Linux/Windows PC using serial port (VCP). and communicating with it using Python and PySerial library.
This tutorial will concentrate on Python 3.x.x language and will use Pyserial 3.4 Library.
First section deals with Arduino and Second section deals with bare microcontrollers like AVR,Microchip and Last section deals with Linux specific details.
Python is an open source, cross platform ,interpreted language that is easy to learn for beginners. One of the many advantages of Python is the sheer number of contributed modules for performing a wide variety of tasks.It is widely used for building scripts/program to interact with real world objects like USB relays,USB data acquisition devices,USB data loggers and other embedded systems.
Easiest way to interact with serial port devices is over a Virtual Com Port using a USB to Serial Converter IC like
- FTDI FT232RL
- TUSB3410
- or CP2102.
Once the necessary drivers are installed you can interact over VCP by reading and writing into it.
One problem with developing code that uses serial port is portability, you can't use the same code in both Windows and Linux. For each operating system (Windows/Linux) you have to write custom codes using the native API's as we have done
- here Win32 Serial Port Programming using Native APi's
- and Linux serialPort programming using Native API's.
Python provides an easy way to do cross platform serial communication using pySerial module.
The modules hides all the OS specific peculiarities and presents a uniform simple interface for programming the serial port. The code written with pySerial can run unmodified on Windows and Linux systems.
Sourcecodes
- Browse Python Serial Comm code from our Github Repo
- Download Python Serial Comm code as zip file
- Please note that the source codes on the website show only the relevant sections to highlight the process of programming the serial port.
- Please use the complete source codes from our github repo when building your own program.
USB2SERIAL - Any easy to use multi protocol converter that can convert from USB to RS485/RS232/Serial.The Board comes with selectable voltage levels for interfacing with 5V and 3.3V logic families.It has screw terminals for easy access to FT232RL pins .3 Pin RS232 and DB9 Male pin for RS232 protocols.
In Windows, Python is not installed by default, you can find python binary installers from either python.org or from ActiveState software.
After completing the installation you can type “python” on your command prompt to enter the python shell. (use CTRL + Z to exit from the shell).
or use GUI based shell IDLE.
Installing PySerial on Windows
After you have installed the python interpreter, You can install PySerial using pip installer.Earlier Pyserial Homepage used to provide Windows Executable file which can be installed using point and click method .Now they are providing source and wheels package only.
Here we will be installing the PySerial Package using pip installer.So open up your Windows Command prompt and type in the following command.
| C:\python -m pip install pyserial |
as shown below
After installing pySerial, open the python shell and type “import serial”.
If you are not getting any error messages, pySerial is installed properly.
Some IDE's like Thonny has built in Python interpretors which work independently from the interpreter installed on your system.
The IDE already has pySerial installed and there is no need for installing it using pip command.
Writing data to Serial Port using Python and pySerial
Now lets open a serial port and write some values to it. The code in python is quite straight forward, you can just read it like plain English.
Open a text editor and type the following lines of code into it .Save the file with a ” .py” extension.
The Below code writes character 'A' to the serial port.
# Python code transmits a byte to Arduino /Microcontroller import serial import time SerialObj = serial.Serial('COM24') # COMxx format on Windows SerialObj.baudrate = 9600 # set Baud rate to 9600 time.sleep(3) SerialObj.write(b'A') #transmit 'A' (8bit) to micro/Arduino SerialObj.close() # Close the port |
The first line import serial imports the pySerial module so that your program can use it.
ComPort = serial.Serial('COM24') opens the serial port named COM24.
In Windows,
Please give the COM number corresponding to your Serial port or USB to Serial Converter instead of COM24.
Opening the serial port using pySerial may reset the Arduino connected on the port,(here COM24).This is specific to Arduino only .
time.sleep(3)
So you should wait some time (here 3 seconds) before transmitting the data to the Arduino board.In the above code we are using time.sleep(3) function.
Serial communication occurs in bytes (8 bits) while Python3+ handles strings in unicode format which may consume upto 4 bytes.
So to make the characters suitable to send to a microcontroller we have to convert them to byte based chunks.
In the above Example we are sending a byte 'A'. Here A is defined as a byte by using b prefix.You can also use the bytearray() function.
SerialObj.write(b'A') #transmit 'A' (8bit) to micro/Arduino
SerialObj.write(b'A') function then writes/sends data to your microcontroller /Arduino.
In Windows,
You can either run the code from command line,
| D:\> python yourSerialTransmitCode.py |
or by using IDLE
From IDLE use “File → Open” to open your code file and from “Run → Run Module”.
Arduino Side Code
PC and Arduino are connected as shown below using a single USB cable.
On the Arduino side ,
we wait for the Character A and turns the LED connected to Pin12 ON for 2 seconds.
A switch() is used to select the required action.
The partial code is shown below.
if (Serial.available()) case 'B': //your code |
Please visit our Github for the full code
Some times opening the serial port may fail due to various conditions like port in use ,port not found etc .
PySerial comes with the exception serial.SerialException which can be used to identify the error and fail gracefully.
The below partial code shows how to use exceptions
| try: SerialObj = serial.Serial('COM11',9600) # open the Serial Port exceptserial.SerialExceptionas var : # var contains details of issue print('An Exception Occured') print('Exception Details-> ', var) else: print('Serial Port Opened') |
Here is an example of the error message you will get
when some other process is using the port you are trying to access.
When Port number is wrong.
%Run is due to the IDE running the code on the terminal
Reading Data from Serial port using Python and Pyserial
PySerial provides two functions to read data from the serialport
- readline()
- read()
readline() reads till it encounters a newline character '\n'and returns the bytes it has read.If \n character is not encountered it will wait forever or until the read timeout expires.
| ReceivedString = SerialObj.readline() print(ReceivedString) SerialObj.close() |
| void loop() { char TextToSend[] = "Hello From Arduino Uno"; Serial.println(TextToSend); // sends a \n with text delay(1000); } |
The Arduino sends a string which is received by the PC side Python code and displayed on terminal.
Please note that only relevant portions of the code are shown above.
Please visit our github repo for full code.
Connecting a Bare Microcontroller to your PC 's Serial port
In the above tutorial we learned how to connect an Arduino board with a PC and communicate with it (Receive/Transmit data ) using a standard USB cable.
What if instead of an Arduino we just want to connect a bare microcontroller like ATmega328P,ATmega16,MSP430 or PIC18F4550 to your PC.
In the case of Arduino all the details of how ATmega328P connects with the USB section is abstracted away from the user,when you are building embedded systems you have to know which signals are connected to which.
When you are using a microcontroller which do not have any built in USB controller like ATmega16 or MSP430G2553 ,you have to use a USB to Serial Converter chip like FT232RL or buy a standard USB to serial converter board like USB2SERIAL to convert serial signals to the USB ones.
The USB2SERIAL board shown can work as a USB to serial Converter,USB to RS232 Converter or USB to RS485 converter
The below block diagram shows how to interface any microcontroller with a standard USB to serial converter.
Here the TXD of the serial port is connected to the RXD of the microcontroller UART and vice versa. So when microcontroller transmits a byte it goes to the receive buffer of the serialport on the PC side and vice versa.
Ground lines are made common to both PC and microcontroller.
MSP430 Microcontroller interface with PC using Python
Above image shows how to hook up a launchpad board with PC using USB2SERIAL converter The Controller (MSP430G2553) is connected to the FT232's Serial port using a null modem cable as shown in the above figure.
Please note that MSP430's are 3.3V microcontrollers ,so please select the IO voltage levels of USB2SERIAL board as 3.3V.
In case you want to know more about MSP430's, check this short tutorial on how to configure MSP430G2553 UART.
ATmega328P Microcontroller interface with PC using Python
Yes, Arduino uno is ATmega328P but here the code is written in AVR embedded C and compiled using AVR studio or Microchip Studio.
- rts
- and dtr
import serial SerialObj = serial.Serial('COM6',9600) SerialObj.rts = 1#RTS HIGH SerialObj.dtr = 1#DTR HIGH SerialObj.close() |
Python Serial programming on Linux