How to fix UnicodeDecodeError when using Serial.println

Question

I am using an Arduino Uno R3 to send instructions to a serial monitor in a Python program with Serial.println. But when I send a specific line, I get a a UnicodeDecodeError.

The line in the Arduino code that causes this error is:

Serial.println("Press '1,2,3,4,5' to run motor at 10%, 20%, 30%, 40%, 50% for 2 seconds");

My Python code to read the serial data is:

def get_serial_data(self):
 while 1:
 try:
 serial_data = self.serial_connection.readline().decode('Ascii')
 filtered_serial_data = serial_data.strip('\r\n')
 self.serial_monitor.insert(END, filtered_serial_data)
 except TypeError:
 pass

and is called from a thread:

thread1 = threading.Thread(target=self.get_serial_data)
 thread1.daemon = True
 thread1.start()

But I get the following error:

UnicodeDecodeError: 'ascii' codec can't decode byte 0x85 in position 36: ordinal not in range(128)

Can anyone help why this is happening or how to fix, I saw a stackoverflow post to use a try, except block to get it to ignore this line, but I want to print it out, and I want to understand why I get this error.

• stanley: As a newcomer to the Arduino community, it would be good to know why this and my answer got downvoted. It was a genuine issue that took me a while to solve, and wasn't obvious from the docs. Without any reasoning for the downvotes makes this community come across as unfriendly

Answer 1

I solved the issue. It was a memory issue not a decoding issue. Because the dynamic memory was mostly used up, it affected the encoding of the data. Reducing the amount of memory my code was using resolved the issue.

I also discovered, that Serial.println("some text") uses a lot of dynamic memory. So by reducing the amount of text I was encoding helped, but also by wrapping the the text in F(), like this:

Serial.println(F("some text"))

Which stores the string in flash memory not sram. Heres a helpful link on the F function:

https://arduinogetstarted.com/faq/what-is-serial.println-f