arduino reading serial from pyserial for stepper motor setspeed

Projects Programming
1

Hey everyone,

I have written the following arduino code to try and read a serial value sent over from pyserial (python). I want the ascii character that I sent over by python to be read by the arduino as an integer value which will then be used as the speed value for the stepper motor.

#include <Stepper.h>

int s = 0;
const int stepsPerRevolution = 48;
Stepper myStepper = Stepper(stepsPerRevolution, 8,9,10,11);

void loop() {
myStepper.step(stepsPerRevolution);
}

void setup() {
Serial.begin(9600);
s = Serial.read()-'NUL'; //convert ascii to int. read from serial port and substract serial 0
myStepper.setSpeed(s);
}

Here is my python code which sends over the speed setting in ascii:

import sys
import serial
import time

ser = serial.Serial('/dev/ttyACM5', 9600)
ser.timeout = 2
ser.open()

s = input('Enter a speed from 0-70')
ser.write('s')

However nothing happens on the arduino front. I have compiled the arduino code which seems to work out fine.

Any suggestions would be greatly appreciated. Much thanks,

Tom

2 
s = Serial.read()-'NUL';

That's not sensible.
What are you trying to do?

3

i want to use python to set the speed of my stepper motor. so basically i want to use pyserial:

serial.write( "number - which will be then be sent to arduino as the speed value for the stepper motor")

Thank you

Tom

4

Mostly, Serial.read is going to return -1.
It's always best to check there's something available to read, before reading it.

5

so all i would need to do is add one more line of code in python to verify what i am sending the correct ascii character?

6

No, I'd add Arduino code to check that there's something available to read, before reading it.
I'm pretty sure it is set out in the examples.

7

so then otherwise everything should look okay? and if there isn't anything sent, what could that possibly mean? what would i then need to do?

I will check the example arduino code as well.

Thanks

8

so then otherwise everything should look okay?

No. That 'NUL' is still wrong. 'NUL' is a multibyte character constant which will not have the value you think it does (whatever it is you think it does).