Serial.read() issue

Projects Programming
1

Hi all.
The project I'm working on is about controlling the speed of a motor connected to a Arduino working as Rx, through a potentiometer on a Arduino working as Tx, all this via the UART port.
The variation of the potentiometer sends a value between 0 and 100, and if this value exceeds 50, an audible alarm is activated.
The problem arises in the arduino Rx, since the value it receives messes it up, for example:

In the ideal world Arduino Tx sends a 20 and Arduino Rx receives a 20
But in reality it receives: 20, then 2, then 20, then 2, then 20, and so on.

At the moment I can't think of how to solve this in the serial reading.
I would appreciate any help with this issue.
Thanks.

My Arduino TX Code:

#define POT A0

long int potentiometer = 0;

void setup() {

  Serial.begin(9600);
  analogReference(DEFAULT);
}

void loop()

{
  potentiometer = analogRead(POT);
  int scaling = map(potentiometer, 0, 1023, 0, 100);
  Serial.print(scaling);
  delay(1000);
}

And my Arduino RX Code:

#define BUZZER 2
#define MOTOR 3

const unsigned int LONG_MAX_MSG = 3;
int number = 0;

void setup() {

  Serial.begin(9600);
  pinMode(BUZZER, OUTPUT); 
  pinMode(MOTOR, OUTPUT);
}

void loop() {

  while (Serial.available() > 0) {

    static char message[LONG_MAX_MSG];
    static unsigned int pos_msg = 0;

    char inByte = Serial.read();

    //Checks if the message it is not a new line
    if (inByte != '\n' && (pos_msg < LONG_MAX_MSG - 1)) {
      message[pos_msg] = inByte;
      pos_msg++;
      delay(100);
    }
    //Mensaje received
    else {
      //Agrega un carácter null al string
      message[pos_msg] = '\0';

       //char to int
      number = atoi(message);
      Serial.println(number);

      //Reinicia la posición del mensaje para la siguiente transmisión
      pos_msg = 0;
      delay(100);

      //Sound alarm
      if (number >= 50) {
        tone(BUZZER, 250);
        analogWrite(MOTOR, number);
        delay(100);
      }
      else{
      noTone(BUZZER);
      analogWrite(MOTOR, number);
      }
      delay(100);
    }
  }
}
2

You're looking for a '\n' in the input but you never sent one. Try changing:
Serial.print(scaling);
in your sending sketch to:
Serial.println(scaling);

3

I think @johnwasser nailed it. However, I am wondering why you are using 2 Arduinos?

4

Thanks for your reply.
When i write with Serial.println(); instead of show me 20, 2, 20, 2 in the Rx Monitor, shows 20, 0, 20, 0, and so on.

1

I forgot to mention that im doing this at tinkercad.

5

It's just a exercise in a postgraduate course.
I'm too proud to drop the exercise if it doesn't work at 100%, and also, this kind of issue teaches a lot.

6

Your input buffer only has room for two characters.

Back when you were sending "2020202020202020" half the time you would read "20" and throw away a '2' because it wouldn't fit in the buffer. The other half the time you'd read "02" and throw away a '0' because it wouldn't fit in the buffer.

Now that you are sending "20\n20\n20\n" half the time you are reading "20" and half the time you are reading "\n".

I would make the input buffer bigger so you can fit at least "100\n\0" before you run out of space.

const unsigned int LONG_MAX_MSG = 6;

7

That did it!
Thank you very much for your help.

I have to remember to consider \n and \o in the buffer size.

8

You also need to earn how to do Serial receive WITHOUT long delay() calls. That is doing nothing but wasting millions of CPU cycles that could be doing useful work. You should read this page, and adopt all of the methods presented therein.

Serial Input Basics - updated - Using Arduino / Introductory Tutorials - Arduino Forum

9

Thanks, i will check that!

10

Here is the real test using two Arduinos (UNO and NANO):

Sender Sketch: using Software UART Port.

t#include<SoftwareSerial.h>
SoftwareSerial SUART(10, 11); //SRX = DPin-10, STX = 17
#define POT A0
int potentiometer = 0;

void setup()
{
  Serial.begin(9600);
  SUART.begin(9600);
  analogReference(DEFAULT);
}

void loop()
{
  potentiometer = analogRead(POT);
  byte scaling = map(potentiometer, 0, 1023, 0, 100);
  SUART.print(scaling);
  Serial.print('\n');
  delay(1000);
}

Receiver Sketch: using Software UART Port.

#include<SoftwareSerial.h>
SoftwareSerial SUART(10, 11); //SRX = DPin-10, STX = 17

#define BUZZER 2
#define MOTOR 3
const unsigned int LONG_MAX_MSG = 3;
int number = 0;
char message[20] = {0};

void setup()
{
  Serial.begin(9600);
  SUART.begin(9600);
  pinMode(BUZZER, OUTPUT);
  pinMode(MOTOR, OUTPUT);
}

void loop()
{
  byte n = SUART.read();
  if (n != 0)
  {
    byte m = SUART.readBytesUntil('\n', message, sizeof message - 1);
    message[m] = '\0';
    number = atoi(message);
    Serial.print(number);
    Serial.println();
    memset(message, 0, 20);
    //Sound alarm
    if (number >= 50)
    {
      tone(BUZZER, 250);
      analogWrite(MOTOR, number);
    }
    else
    {
      noTone(BUZZER);
      analogWrite(MOTOR, number);
    }
  }
}

Receiver SM: as the Pot at Sender side is rotated.

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11

This is a rather special case, since you are only sending a single value, but you can simply send the binary value as a single byte, and not have to worry about line endings or ascii conversions.

12

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