Pyserial serial.write() doesn't work

Question

I need to communicate with an Arduino. Doing serial.readline() to read what Arduino has to say works fine. Doing serial.write('something') doesn't seem to do anything.

What is interesting is that if I write the same code in the console or command-line, it works as expected...

Using Python 2.7.

Python code:

import time
import serial

# setup Arduino USB communication
try:
    arduinoSerialData = serial.Serial('com3', 9600)

except: # not connected/damaged
    pass

while True:
    if arduinoSerialData.inWaiting() > 0:
        arduinoSerialData.write('A')
        arduinoSerialData.flush()
        datastr = arduinoSerialData.readline()
        print datastr
        time.sleep(1)

this does not include any information that we would need to help you. Be more specific on what is not working and post any code that could help us. — Azsgy
– Azsgy, Commented Sep 20, 2015 at 19:21
Doesn't flush() freeze the program? My program has a main loop. I'll update the post with a code. — Leo Ervin
– Leo Ervin, Commented Sep 20, 2015 at 19:25
If you don't have flow-control disabled, then pyserial could be vainly waiting for CTS to be active. — Patrick Maupin
– Patrick Maupin, Commented Sep 20, 2015 at 19:28

Bryan · Accepted Answer · 2018-02-28 01:59:05Z

5

Put a time.sleep(2) line after you open the port to give the Arduino time to reboot.

edited Feb 28, 2018 at 1:59

Bryan

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answered Feb 28, 2018 at 1:56

Daniel Espitia

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Comments

Daniel · Accepted Answer · 2021-08-15 10:37:09Z

I know I´m a little bit too late but today I had the same problem with Pyserial and an ESP32, a device sort of like an arduino. The solution was to give pyserial the same configuration as the serial interface in the ESP32:

esp = serial.Serial("COM10", 115200)
esp.parity=serial.PARITY_EVEN
esp.stopbits=serial.STOPBITS_ONE
esp.bytesize=serial.EIGHTBITS

I send the commands like this:

arr = [32,2,0,4] #Decimal
esp.write(arr)

This is the ESP32 configuration, in case you need to know:

uart_config_t uart_config = {
        .baud_rate = 115200,
        .data_bits = UART_DATA_8_BITS,
        .parity    = UART_PARITY_EVEN,
        .stop_bits = UART_STOP_BITS_1,
        .flow_ctrl = UART_HW_FLOWCTRL_DISABLE
};
    
uart_param_config(UART_PORT_NUM, &uart_config);

The ESP now echoes the command correctly I hope this can help.

Hamza Boughraira · Accepted Answer · 2015-09-21 01:25:34Z

0

try to add the timeout parameter in the Python script, then try to set your main arduino code in a while loop step1: python

 arduinoSerialData = serial.Serial('com3', 9600, 1)

replace the arduinoSerialData.flush() by:

 arduinoSerialData.flushInput()

step2: Arduino:

void loop(){
    while (Serial.available > 0){
            // your main code
    }
}

answered Sep 21, 2015 at 1:25

Hamza Boughraira

752 gold badges2 silver badges7 bronze badges

3 Comments

Leo Ervin Over a year ago

I also use the arduino to tell the state of 6 buttons, which I'd like to check every 0.5 seconds. WIll that be an issue with this solution?

Leo Ervin Over a year ago

Yeah, arduinoSerialData.readline() after write() kills the performance of the program...

Hamza Boughraira Over a year ago

try to clear the serial buffer after reading from the arduino, this will not kill the performance of the program

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