Stuck Python to Arduino Serial

[swilker]

Running Ubuntu on a Pi 2 wrote this code in python:

import serial
test=serial.Serial("/dev/ttyACM0",9600)
test.write('3')

It's sending something, but I need it to send the number 3 to the Arduino and it's definitely not sending that.
I've tested the Arduino code from my MAC and I open a serial window type in a 3 and get three blinks.

Please Help been stuck for hours probably an easy fix.

[gordon77]

Try

test.write(bytes("3".encode('ascii')))

[swilker]

Thanks you for your help, however I had already tried that. Just in case I did it again, still doesn't work. Light blinks, but blinking not related to number sent.

[gordon77]

What light doesn't blink?

What code is in the Arduino?

[alexeames]

That serial port address looks wrong to me. Shouldn't it be AMA0? Working from memory here as I'm not at my computer

[dobra-dobra]

Shouldn't it be AMA0?

Yes, it should.

Code: Select all

test = serial.Serial()
test.baudrate = 9600
test.timeout = 0
test.port = "/dev/ttyAMA0"

Before sending message you should open the port:

Code: Select all

test.open()

Then if you are using Python 2:

Code: Select all

test.write("3")

But for Python 3 it will be:

Code: Select all

test.write("3".encode()

[swilker]

test.open() gives an error
Yes python 2
ls /dev/tty* returns ACM0 not AMA0 as the new connection
test.write("3".encode()) same result, light blinks once

const int ledPin = 13;
void setup(){
pinMode(ledPin, OUTPUT);
Serial.begin(9600);
}
void loop(){
if (Serial.available()) {
light(Serial.read() – ‘0’);
}
delay(500);
}
void light(int n){
for (int i = 0; i < n; i++) {
digitalWrite(ledPin, HIGH);
delay(100);
digitalWrite(ledPin, LOW);
delay(100);
}
}

[swilker]

Solution:
import serial
import time
test= serial.Serial("/dev/ttyACM0",9600)
time.sleep(2)
test.write("3".encode('ascii'))

requires time.sleep(2) to allow arduino to reset on connect. Found it on OscarLiang.net
http://blog.oscarliang.net/connect-rasp ... usb-cable/

[gordon77]

That serial port address looks wrong to me. Shouldn't it be AMA0? Working from memory here as I'm not at my computer

an Arduino R3 uses ACM0 when connected by usb.

[dobra-dobra]

Glad you were able to sort it out. I thought that you are trying to use Rx/Tx pins on GPIO to connect, not USB port. But USB port is safer option due to the voltage difference (5 V Arduino vs. 3.3 V RPi).

[DougieLawson]

That serial port address looks wrong to me. Shouldn't it be AMA0? Working from memory here as I'm not at my computer

Not if the Arduino is connected to the USB it isn't. It's /dev/ttyACMx. /dev/ttyAMA0 is the Raspberries UART on pins #8 & #10, you'd need a level shifter to connect a 5V0 Arduino to that.

[alexeames]

That serial port address looks wrong to me. Shouldn't it be AMA0? Working from memory here as I'm not at my computer

an Arduino R3 uses ACM0 when connected by usb.

Thanks. That's good to know. The OP didn't say he'd connected by USB or what kind of arduino it was so I just chipped in with what I knew in case it was an obvious "is there petrol in the tank" mistake