get data from arduino using python

Question 1

I am trying toread potential meter data from Arduino using python, with the program on Arduino as follows :

#include <cvzone.h>SerialData serialData;int sendVals[2];void setup() {  serialData.begin(9600);}void loop() {  int potVal = analogRead(A0);  sendVals[0]= potVal;  serialData.Send(sendVals);}

the program on the arduino side is running fine

and program in python as follows

from cvzone.SerialModule import SerialObjectarduino = SerialObject("COM7")while True:   data = arduino.getData()   print(data[0])

but I get this error:

Traceback (most recent call last):    data = arduino.getData()  File "C:...\site-packages\cvzone\SerialModule.py", line 68, in getData    data = data.decode("utf-8")UnicodeDecodeError: 'utf-8' codec can't decode byte 0xf7 in position 0: invalid start byte

How to solve it?

Question 2

the new USB connection resets the Mega and it spends some time in bootloader waiting for upload.

Question 3

Maybe add some delay on the Arduino after initializing the serialData instartup() before it starts sending data in theloop().

Question 4

I would embed the call to.getData() into atry block and handle this specific exception withexcept UnicodeDecodeError. There can always be a transmission error, especially when the script is started.

However, I would do it differently:

void loop() {  Serial.println(analogRead(A0));}

...and on the python side useserial.readline() from pyserial instead.But I don't know cvzone and you might have a reason to use this instead of the commonly used pyserial.

Question 5

There seems that theremay be an issue with the implementation ofgetData() inSerialModule.py.

Fromline 62

    def getData(self):        """        :param numOfVals: number of vals to retrieve        :return: list of data received        """        data = self.ser.readline()        data = data.decode("utf-8")        data = data.split('#')        dataList = []        [dataList.append(d) for d in data]        return dataList[:-1]

The block of code containing thereadLine() should probably be with in atry...except block, like so:

    def getData(self):        """        :param numOfVals: number of vals to retrieve        :return: list of data received        """        try:            data = self.ser.readline()            data = data.decode("utf-8")            data = data.split('#')            dataList = []            [dataList.append(d) for d in data]            return dataList[:-1]        except Exception as e:            print(e)            self.ser.close

An issue has been raised on Github:SerialModule.py - readLine() should be within try block. #49

Sim Son 1,87814 silver badges21 bronze badges · Accepted Answer · 2021-12-06 13:35:30Z

I would embed the call to.getData() into atry block and handle this specific exception withexcept UnicodeDecodeError. There can always be a transmission error, especially when the script is started.

However, I would do it differently:

void loop() {  Serial.println(analogRead(A0));}

...and on the python side useserial.readline() from pyserial instead.But I don't know cvzone and you might have a reason to use this instead of the commonly used pyserial.

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