Unable to read data from serial port

Question

I tried to read data from USB port on OSX using pyserial. When I tried to read it using CoolTerm, everything worked fine. This is the configuration:

Then I tried to write a short script which doesn't continuously output the data (it outputs the data only once and the even if I restart the script, nothing comes out):

import serial
import time

ser = serial.Serial("/dev/cu.SLAB_USBtoUART", 115200, timeout=5, bytesize=8, stopbits=serial.STOPBITS_ONE, parity=serial.PARITY_NONE)


def getTFminiData():
    while True:
        # time.sleep(0.1)
        count = ser.in_waiting
        if count > 8:
            recv = ser.read(9)
            ser.reset_input_buffer()

            if recv[0] == 0x59 and recv[1] == 0x59:  # python3
                distance = recv[2] + recv[3] * 256
                strength = recv[4] + recv[5] * 256
                print('(', distance, ',', strength, ')')
                ser.reset_input_buffer()


if __name__ == '__main__':
    try:
        if ser.is_open == False:
            ser.open()
        getTFminiData()
    except KeyboardInterrupt:  # Ctrl+C
        if ser != None:
            ser.close()

Does anyone know what is the right way to get the same data as CoolTerm in this case does?

You probably need to read all data up to a new line separator. Try to use the function `readline()` — Joe, Oct 04 '19 at 09:59
@joe, I tried to use readLine, but the execution stops at that line — Niko Gamulin, Oct 04 '19 at 10:01
Then it is waiting for the line separating character. Do you know what it looks like? — Joe, Oct 04 '19 at 10:34
If you know you can try or modify my answer https://stackoverflow.com/a/56240817/7919597 — Joe, Oct 04 '19 at 10:35

score 0 · Accepted Answer · answered Oct 04 '19 at 11:32

Thanks to Joe's comment, I fuggered out how to modify the code. The working example is the following:

import serial
import time

ser = serial.Serial("/dev/cu.SLAB_USBtoUART", 115200, bytesize=8, stopbits=serial.STOPBITS_ONE, parity=serial.PARITY_NONE)


def getTFminiData():
    bytes_read = 0
    data = None
    while True:
        # time.sleep(0.1)
        count = max(1, ser.in_waiting)
        if count < 8:
            if data is None:
                data = ser.read(count)
            else:
                data.append(ser.read(count))
            bytes_read += count

        else:
            recv = ser.read(9 - bytes_read)
            bytes_read = 0
            recv = data + recv
            data = None
            ser.reset_input_buffer()

            if recv[0] == 0x59 and recv[1] == 0x59:  # python3
                distance = recv[2] + recv[3] * 256
                strength = recv[4] + recv[5] * 256
                print('(', distance, ',', strength, ')')
                ser.reset_input_buffer()


if __name__ == '__main__':
    try:
        if ser.is_open == False:
            ser.open()
        getTFminiData()
    except KeyboardInterrupt:  # Ctrl+C
        if ser != None:
            ser.close()

Unable to read data from serial port

1 Answers1