Send Data from Arduino to Processing over serial // help please

Casey_Scalf

I am trying to send data from an Arduino Uno to Processing.

Video of situation:

I made a simple sketch which does this no problem. It is only when I try to have the Arduino send data to Procesing in an "if conditional" from an analog sensor reading that I run into trouble.

For instance, the simple send from Arduino looks like this:

int ledPin = 13;

void setup()
{
  Serial.begin(9600);
   pinMode(ledPin, OUTPUT);
}
void loop()
{
  Serial.write(1);
   digitalWrite(ledPin, HIGH);
  delay(200);
  Serial.write(0);
   digitalWrite(ledPin, LOW);
  delay(200);
}

And the corresponding Processing code looks like this:

import processing.serial.*;

Serial myPort;  // Create object from Serial class
int val;

void setup() {
  //change the 0 to a 1 or 2 etc. to match your port
  String portName = Serial.list()[2]; 
  myPort = new Serial(this, portName, 9600);

  rectMode(CENTER);
}

void draw()
{
  background(0);
  fill(255);

  if (myPort.available()>0)
  {
    val = myPort.read();
  }
  println(val);

  if (val == 1)  {
    rect(width/2, height/2, 30, 30);
  }
}

It makes a white square appears when the number "1" is sent to Processing. It works so simple. It works every time. I was so pleased.

However, when I try it with the next Arduino sketch, nothing ever happens. It always stays on "0" even though I can see on the Arduino the LED turns on showing that yes, this piece of code has run. The Processing portion can stay exactly the same.

Why am I not seeing it work right? I have tried so many things. This tells me it's either painfully obvious or I've done something horribly karmically wrong and this is my punishment.

Thank you for nay tips.

    // Used to interface with electronic drum pads
    // Using a piezo sensor
    // Casey Scalf 2015


    int ledPin = 13;
    int padPin = 0; // Red
    // Black is Ground

    byte val;
    byte a = 0;

    int THRESHOLD = 20;

    void setup() {

      Serial.begin(9600);

      pinMode(ledPin, OUTPUT);
    }

    void loop() {

      val = analogRead(padPin);

      if (val <= THRESHOLD) {
        digitalWrite(ledPin, LOW);
        a = 0;
        Serial.write(a);
      }

        if (val >= THRESHOLD) {
        digitalWrite(ledPin, HIGH);
        a = 1;
        Serial.write(a);
      }

    }

Chrisir

delay(200);

?

Chrisir

?

Chrisir

Replace <= with < pls

Because = twice is ambigous

Also when have this kind of code try

if .... .... else if .....

You don't use else if

Casey_Scalf

Thanks Chrisir.

The delay is to show that by alternating the Serial.write slowly it will successfully send the message.

I will try the comparison symbol and play with the if/else if combination.

A friend was saying that it might be because the Arduino is simply sending the message too fast for Processing to pick up. (i.e. 120 fps vs 30 fps)

joepekoe

Try adding Serial.flush() immediately after Serial.write()

Any reason you are not using Serial.print()?

Casey_Scalf

Hi Joepekoe, I will try that. I am actually reinvestigating this now since the summer is over and I have some free time. I think the biggest thing we ran into was that the data is coming over too fast.

I will advise after more testing. Thank you for your suggestion.

benja

I guess you are on the right track. Always put a delay() inside of your arduino-sketch or control the amount of data sent by any other kind of timing. The arduino has no fixed framrate like processing and the number of loop()-cycles beeing executed per second depends on the code that is executed.

Without delays, it can happen that thousands of values/messages are sent every second. So when you read one value per frame at a framrate of 60 in processing, it can take minutes to process all the serial-data that has been sent in the first second of your arduino sketch.

Casey_Scalf

Good call. That's essentially the battle.

As noted above i'm using this with an electronic drum pad. So timing is key.

Given that a fair amount of people will want to send data from an Arduino to their computer I'm surprised that this doesn't comes up more often/the existence of an established way to deal with this - especially with such trivially simple data (on or off when a switch is flipped).

Should have time tomorrow or the next day!

benja

It is a common topic. In a case like yours, where you don't need continous data, i would only send messages as soon as the state (on/off) of your pad changes. Example:

int ledPin = 13;
int padPin = A0;
boolean padOn = false;

int THRESHOLD = 20;

void setup() {
  pinMode(padPin, INPUT_PULLUP);
  pinMode(ledPin, OUTPUT);
  Serial.begin(9600);
}

void loop() {

  int val = analogRead(padPin);

  // only do something, when value is below threshold AND it was above before 
  if (val <= THRESHOLD && padOn) {
    digitalWrite(ledPin, LOW);
    Serial.write('0');
    padOn = false;
  }
  // only do something, when value is above threshold AND it was below before 
  else if (val > THRESHOLD && !padOn) {
    digitalWrite(ledPin, HIGH);
    Serial.write('1');
    padOn = true;
  }
  // a small delay is a good idea in most situations
  delay(5);
}

And in processing i prefer the serialEvent()-function to handle incoming serial-data.

GoToLoop

Me too on serialEvent(). Lotsa forum threads using it: :D
http://forum.Processing.org/two/discussions/tagged?Tag=serialEvent()

Casey_Scalf

Excellent points, I look forward to round 2 tonight!

Casey_Scalf

That worked like a charm!

I ended up using a button so I could keep the setup simple while experimenting. This works great. I think it was the "padOn" boolean trick that made it happen.

Casey_Scalf

Here is the Arduino Code:

//  http://www.arduino.cc/en/Tutorial/Button
// Slightly modified to send over Serial
// http://forum.processing.org/two/discussion/11649/send-data-from-arduino-to-processing-over-serial-help-please#latest

// constants won't change. They're used here to
// set pin numbers:
const int buttonPin = 2;     // the number of the pushbutton pin
const int ledPin =  12;      // the number of the LED pin
boolean padOn = false;

// variables will change:
int buttonState = 0;         // variable for reading the pushbutton status

void setup() {
  // initialize the LED pin as an output:
  pinMode(ledPin, OUTPUT);
  // initialize the pushbutton pin as an input:
  pinMode(buttonPin, INPUT);
  // Starts Serial
  Serial.begin(9600);
}

void loop() {
  // read the state of the pushbutton value:
  buttonState = digitalRead(buttonPin);

  // check if the pushbutton is pressed.
  // if it is, the buttonState is HIGH:
  if (buttonState == HIGH && padOn) {
    // turn LED on:
    digitalWrite(ledPin, HIGH);
    Serial.write('0');
    padOn = false;
  } else if (buttonState == LOW && !padOn) {
  // turn LED off:
  digitalWrite(ledPin, LOW);
    Serial.write('2');
    padOn = true;
  }

  // a small delay is a good idea in most situations
  delay(5);
}

Casey_Scalf

And the Processing Code:

// Used to receive signals from an Arduino over Serial
// Casey Scalf 2015

import processing.serial.*;

Serial myPort;  // Create object from Serial class
int val;

void setup() {
  size(300, 200);
  frameRate(60);

 // Use with "Simple_Button_Send"
 // http://forum.processing.org/two/discussion/11649/send-data-from-arduino-to-processing-over-serial-help-please#latest

 //change the 0 to a 1 or 2 etc. to match your port
  String portName = Serial.list()[2]; 
  myPort = new Serial(this, portName, 9600);

  rectMode(CENTER);
}

void draw()
{
  background(0);
  fill(255);

  if (myPort.available()>0)
  {
    val = myPort.read();
    println(val);
  }

  if (val == 48)  {
    rect(width/2, height/2, 60, 30);
  }
}