Raspberry和Arduino来回交谈

Question

I'm working on a project in which I am using an Arduino to simulate another device that will be connected to the Raspberry. I have managed to do get the Raspberry to control the Arduino (by blinking some LED's in a pattern the Pi controlled). Now I'm looking to exchange data back and forth and have written programs for the Pi and Arduino that should have them receiving a number and then adding 1 to that number and send it back.

Raspberry Pi:

import serial
import time 
ser = serial.Serial('/dev/ttyACM0',9600)
time.sleep(1)
var = b'0'
var2 = b'1'
while 1:
    time.sleep(0.5)
    ser.write(var)
    var = ser.read(ser.inWaiting()) #Wait for Arduino to respond
    print(var)
    var = var + var2
    print('2') #Check print

Arduino:

const int ledPin = 12;
const int ledPin2 = 11;
int n;

void setup() {
  pinMode(ledPin, OUTPUT);
  pinMode(ledPin2, OUTPUT);
  digitalWrite(ledPin2, LOW);
  Serial.begin(9600);
  n = 0;
}

void loop() {
  while(Serial.available() == 0){
    digitalWrite(ledPin, HIGH); //Check LED
  }
  n = Serial.read() - '0';
  digitalWrite(ledPin, LOW);
  n = n + 1;
  Serial.print(n);
}

The resulting print out in python is:

b''
2
b'1'
2
b'2'
2
b'22'
2
b'32'
2
b'332'
2
b'432'
2

And so on. This is not really the sequence I was expecting (1,3,5,7,9,11... Because we start at 0 and print when Arduino have added).

Hope that someone can help. Thank you in advance ^^

Answer 1

ser.read presumably returns a string, which results in (for example) "1" + "2" (aka "12" ). Wrap it in int(): var = int(ser.read(ser.inWaiting()))

The Arduino code will also choke on a number longer than one digit; see https://www.arduino.cc/en/Tutorial.StringToIntExample for how to read an int from serial. Basically keep reading and adding it onto the end of the string until you hit a terminator (the example uses a newline), then call .toInt() on that string.

You could also use something like the following, which is probably more efficient, but certainly less readable:

while (Serial.available() > 0) {
    int inChar = Serial.read();
    if (isDigit(inChar)) {
        int inNum = inChar - '0';
        n = n*10 + inNum;
    } else {
        // if inChar is NOT a digit
    }
}