Pyserial to Arduino problem

1

Hello, I am Having trouble with Pyserial and Arduino. Started reading about Python/Pyserial to arduino, followed the links passed on from forum post DE2120 Scanner, and installed Python3 no problem. Pyserial was not as easy, after many different attempts I installed using sudo easy in the install line which worked.

Following the link https://www.instructables.com/Interface-Python-and-Arduino-with-pySerial/
I copied code for Arduino uploaded, no problem, but when I use the python script I get errors:

… print ser.readline() # Read the newest output from the Arduino
File “”, line 4
print ser.readline() # Read the newest output from the Arduino
^
SyntaxError: invalid syntax

 sleep(.1) # Delay for one tenth of a second

File “”, line 1
sleep(.1) # Delay for one tenth of a second
IndentationError: unexpected indent

 if counter == 255:

File “”, line 1
if counter == 255:
IndentationError: unexpected indent

 counter = 32

Here is the whole thing:

import serial
ser = serial.Serial(‘/dev/tty.usbmodem14101’, 115200) # Establish the connection on a specific port
counter = 32 # Below 32 everything in ASCII is gibberish
while True:
… counter +=1
… ser.write(str(chr(counter))) # Convert the decimal number to ASCII then send it to the Arduino
… print ser.readline() # Read the newest output from the Arduino
File “”, line 4
print ser.readline() # Read the newest output from the Arduino
^
SyntaxError: invalid syntax
sleep(.1) # Delay for one tenth of a second
File “”, line 1
sleep(.1) # Delay for one tenth of a second
IndentationError: unexpected indent
if counter == 255
File “”, line 1
if counter == 255
IndentationError: unexpected indent
counter = 32
I don’t know Python, but after changing, print ser.readline() to print (ser.readline) and if counter == 255: to if counter == 255 I have this:
Last login: Fri Dec 18 09:33:50 on ttys000
@Jasons-MacBook-Pro ~ % python3
Python 3.9.1 (v3.9.1:1e5d33e9b9, Dec 7 2020, 12:44:01)
[Clang 12.0.0 (clang-1200.0.32.27)] on darwin
Type “help”, “copyright”, “credits” or “license” for more information.
from time import sleep
import serial
ser = serial.Serial(‘/dev/tty.usbmodem14101’, 115200) # Establish the connection on a specific port
counter = 32 # Below 32 everything in ASCII is gibberish
while True:
… counter +=1
… ser.write(str(chr(counter))) # Convert the decimal number to ASCII then send it to the Arduino
… print (ser.readline) # Read the newest output from the Arduino
… sleep(.1) # Delay for one tenth of a second
… if counter == 255
File “”, line 6
if counter == 255
^
SyntaxError: invalid syntax
counter = 32

Arduino compiled fine.
Code for Arduino :
void setup() {
Serial.begin(115200); // set the baud rate
Serial.println(“Ready”); // print “Ready” once
}
void loop() {
char inByte = ’ ';
if(Serial.available()){ // only send data back if data has been sent
char inByte = Serial.read(); // read the incoming data
Serial.println(inByte); // send the data back in a new line so that it is not all one long line
}
delay(100); // delay for 1/10 of a second
}

I feel like there is either, a minor error in Python code, Pyserial has had install issues, something has changed from Py 2.7 to Py 3.9, or my system isn’t correct because I see : @Jasons-MacBook-Pro ~ % (I deleted my full Name) instead of : @Jasons-MacBook-Pro ~ $, the default setting is /bin/zsh.

2

Also the Tx led on Arduino is flashing but not receiving in Py.

Can anyone help please.
Thank you.
Jason

3

Have been trying different code, I now have something that does something, but not what it is supposed to do. Here is new code:
from time import sleep
import serial
ser = serial.Serial(’/dev/tty.usbmodem14101’, 115200)
counter = 32
while True:
counter +=1
ser.write(str.encode(chr(counter)))
print (ser.readline)
sleep(.1)
counter == 255
counter = 32

and this is readout:
False
1
<built-in method readline of Serial object at 0x10775bf70>
^CTraceback (most recent call last):
File “”, line 5, in

Any help would be great,
Jason

4

Ok, Here is Python3 code that will give the correct printout:

>>> from time import sleep
>>> import serial
>>> ser = serial.Serial('/dev/tty.usbmodem14101', 115200)
>>> counter = 47 
>>> while True:
...      counter += 1
...      chr(counter)
...      if counter == 57:
...          counter = 47      
...          ser.write(str.encode(chr(counter)))
...          print(str(ser.readline))                 
...          sleep(5)
... 
'0'
'1'
'2'
'3'
'4'
'5'
'6'
'7'
'8'
'9'
1
<built-in method readline of Serial object at 0x1070deb50>

As you can see this is a little different to the original dowloaded from the instuctables link.
I hope this can help anyone with similar issues, (and doesn’t know Py3).
And now back to my actual project.

Jason

2 Likes
5

good to hear you got it sorted. If you any more questions please feel free to post them up

6

Its because in Python 3, print statement has been replaced with a print() function, with keyword arguments to replace most of the special syntax of the old print statement. But if you write this in a program and someone using Python 2.x tries to run it, they will get an error. To avoid this, it is a good practice to import print function:

from __future__ import print_function

Now your code works on both python2 and python3

4 Likes