Button switch Arduino to Processing: serial output giving null

Question

I am trying to use a button switch in Arduino to trigger a visual display in Processing. I used "HIGH" and "LOW" to identify whether the button is pressed.

However, my code is constantly giving null instead of giving "HIGH" or "LOW" depending on the button state. I think this is pretty basic but I'm just quite lost. Any helps or comments would be appreciated!

Below is my code for Arduino and Processing respectively.

const int buttonPin = 2; 
const int LEDPin = 13; 

int buttonState = 0; 

void setup() {
  pinMode(buttonPin, INPUT);
  pinMode(LEDPin, OUTPUT);
  Serial.begin(9600);
}

void loop() {
  int analogValue = analogRead(A0)/4;
  Serial.write(analogValue);
  buttonState = digitalRead(buttonPin);
  if (buttonState == HIGH) {
    Serial.write(HIGH);
    digitalWrite(LEDPin, HIGH);
  } else {
    Serial.write(LOW);
    digitalWrite(LEDPin, LOW);
  }
  delay(100);
}

Processing code:

import processing.serial.*;
Serial myPort;
String val; 

void setup() {
  size(400,400);
  String portName = Serial.list()[1];
  myPort = new Serial(this, portName, 9600);
}

void draw() {
  if (myPort.available() > 0) {
    val = myPort.readStringUntil('\n');
    println(val);
    if (val == "HIGH") {
      background(127,0,0);
    }
    if (val == "LOW") {
      background(144, 26, 251);
    }
  }
}

Serial.write(HIGH); doesn't send 'H','I','G','H' and '\n' but just a 1. — gre_gor
– gre_gor, Commented Nov 28, 2017 at 23:30

gre_gor · Accepted Answer · 2017-11-29 03:26:01Z

2

write()

Writes binary data to the serial port. This data is sent as a byte or series of bytes.

Serial.write(str)

str: a string to send as a series of bytes

So when you use write HIGH and LOW in Serial.write, it will be send as a series of bytes. Edit your processing part to handle the incoming bytes. Just as follows :

import processing.serial.*;
Serial myPort;
String val; 
int len; //length of byte array

void setup() {
  size(400,400);
  String portName = Serial.list()[1];
  myPort = new Serial(this, portName, 9600);
}

void draw() {
  if ((len=myPort.available()) > 0) {
    for(i=0;i<len;i++)
      myByteArray=myPort.read();
    String val = String(myByteArray);
    println(val);
    if (val == "HIGH") {
      background(127,0,0);
    }
    if (val == "LOW") {
      background(144, 26, 251);
    }
  }
}

edited Nov 29, 2017 at 3:26

gre_gor

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answered Nov 29, 2017 at 2:45

Mathews Sunny

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1 Comment

gre_gor Over a year ago

This is wrong. HIGH and LOW will be sent as a single byte 1 and 0. Also this isn't really a reliable way of reading a complete string.

user8890895 · Accepted Answer · 2017-11-29 14:02:44Z

2

just change your buttonState variable type from integer to boolean, and then use

if(buttonState) {
       Serial.println("HIGH");
}
else {
      Serial.println("LOW");
}

answered Nov 29, 2017 at 14:02

user8890895

Comments

gre_gor · Accepted Answer · 2017-11-29 03:23:43Z

1

In Arduino, HIGH and LOW are defined as 1 and 0.

By executing Serial.write(HIGH); and Serial.write(LOW); you are just sending a single byte 1 or 0.

But according to your Processing code, you are expecting Serial.write(HIGH); to send 'H', 'I', 'G', 'H' and '\n' characters.

In your Arduino code, you need to replace Serial.write(HIGH); and Serial.write(LOW); with Serial.print("HIGH\n"); and Serial.print("LOW\n");.

answered Nov 29, 2017 at 3:23

gre_gor

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