TypeError: cannot unpack non-iterable NoneType object

[renzha]

I try to use python to do data logging from an arduino nano. The code works only for several loops, then a error poped up. I am wondering what cause the problem.

The error message:

('5', 1874.8682350429337)
------
('3', 1167.271553440443)
------
('3', 1233.2207809135466)
------
Traceback (most recent call last):
  File "/Users/renzha/Library/Application Support/JetBrains/PyCharmCE2021.1/scratches/stream arduino and save files.py", line 262, in <module>
    t, V = request_single_voltage (arduino)
TypeError: cannot unpack non-iterable NoneType object

Process finished with exit code 1

python code

while True:
    for n in range (0, 11):
        names = ['test', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'end' ]
        for name in names:
            
            VOLTAGE_REQUEST = 200


            arduino = serial.Serial (port, baudrate=115200)


         
            arduino.write (bytes ([VOLTAGE_REQUEST]))

     
            raw = arduino.read_until ()


            def parse_raw(raw):
                         raw = raw.decode ()
                if raw [-1] != "\n":
                    raise ValueError (
                        "Input must end with newline, otherwise message is incomplete."
                    )
                if raw [0] == "0":
                    pass
                try:
                    t, V = raw.rstrip ().split (",")

                    return int(t), int(V)*5/1023
                except ValueError:
                    pass

            def request_single_voltage(arduino):
                """Ask Arduino for a single data point"""
                # Ask Arduino for data
                arduino.write (bytes ([VOLTAGE_REQUEST]))

                # Read in the data
                raw = arduino.read_until ()

                # Parse and return
                return parse_raw (raw)

arduino code

const int voltagePin = A0;
//const int HANDSHAKE = 0;
const int VOLTAGE_REQUEST = 200;

int inByte;
unsigned long time_us;
unsigned long currentTime;
unsigned long startTime;

void printVoltage() {
  // Delay to get to an even millisecond
  delayMicroseconds(1000 - (millis() % 1000));
  startTime = millis();

  for (int i = 0; i < 8000; i++)
  {
    // Delay to get to an even millisecond
    //delayMicroseconds(1000 - (millis() % 1000));
    time_us = millis() - startTime;

    // Read value from analog pin
    int value = analogRead(voltagePin);

    // Write the result
    Serial.print(time_us);
    Serial.print(',');
    Serial.println(value);
  }
}


void setup() {
  // Initialize serial communication
  Serial.begin(115200);

}


void loop() {

  // Check if data has been sent to Arduino and respond accordingly
  if (Serial.available() > 0) {
    // Read in request
    inByte = Serial.read();

    // If data is requested, fetch it and write it, or handshake
    switch (inByte) {
      case VOLTAGE_REQUEST:
        printVoltage();
        break;
        //case HANDSHAKE:
        //if (Serial.availableForWrite()) {
        //Serial.print(""); //Please input:
    }
    //break;
  }
}

[J-M-L]

Possibly a Serial communication challenge

You should check what you read, back from arduino, maybe you timed out or saturated the buffer etc…

[johnwasser]

My guess would be that your python 'parse_raw' function is detecting some kind of invalid input. Perhaps after raw = arduino.read_until () you should display the raw text. Then you can tell if the data received from the Arduino is wrong to the parsing is wrong.