Serial Call and Response (handshaking)

This example demonstrates multi-byte communication from the Arduino or Genuino board to the computer using a call-and-response (handshaking) method.

This sketch sends an ASCII A (byte of value 65) on startup and repeats that until it gets a serial response from the computer. Then it sends three sensor values as single bytes, and waits for another response from the computer.

You can use the Arduino Software (IDE) serial monitor to view the sent data, or it can be read by Processing (see code below), Flash, PD, Max/MSP (see example below), etc.

Hardware Required

  • Arduino or Genuino Board

  • 2 analog sensors (potentiometer, photocell, FSR, etc.)

  • pushbutton

  • 3 10K ohm resistors

  • hook-up wires

  • breadboard

Software Required

Circuit

Connect analog sensors to analog input pin 0 and 1 with 10K ohm resistors used as voltage dividers. Connect a pushbutton or switch to digital I/O pin 2 with a 10K ohm resistor as a reference to ground.

click on the image to enlarge

SerialCallResponse circuit3

image developed using Fritzing. For more circuit examples, see the Fritzing project page

Schematic

click the image to enlarge

SerialCallResponse sch

Code


/*

  Serial Call and Response

  Language: Wiring/Arduino

  This program sends an ASCII A (byte of value 65) on startup and repeats that

  until it gets some data in. Then it waits for a byte in the serial port, and

  sends three sensor values whenever it gets a byte in.

  The circuit:

  - potentiometers attached to analog inputs 0 and 1

  - pushbutton attached to digital I/O 2

  created 26 Sep 2005

  by Tom Igoe

  modified 24 Apr 2012

  by Tom Igoe and Scott Fitzgerald

  Thanks to Greg Shakar and Scott Fitzgerald for the improvements

  This example code is in the public domain.

  http://www.arduino.cc/en/Tutorial/SerialCallResponse

*/

int firstSensor = 0;    // first analog sensor
int secondSensor = 0;   // second analog sensor
int thirdSensor = 0;    // digital sensor
int inByte = 0;         // incoming serial byte

void setup() {

  // start serial port at 9600 bps:

  Serial.begin(9600);

  while (!Serial) {

    ; // wait for serial port to connect. Needed for native USB port only

  }

  pinMode(2, INPUT);   // digital sensor is on digital pin 2

  establishContact();  // send a byte to establish contact until receiver responds
}

void loop() {

  // if we get a valid byte, read analog ins:

  if (Serial.available() > 0) {

    // get incoming byte:

    inByte = Serial.read();

    // read first analog input, divide by 4 to make the range 0-255:

    firstSensor = analogRead(A0) / 4;

    // delay 10ms to let the ADC recover:

    delay(10);

    // read second analog input, divide by 4 to make the range 0-255:

    secondSensor = analogRead(1) / 4;

    // read switch, map it to 0 or 255L

    thirdSensor = map(digitalRead(2), 0, 1, 0, 255);

    // send sensor values:

    Serial.write(firstSensor);

    Serial.write(secondSensor);

    Serial.write(thirdSensor);

  }
}

void establishContact() {

  while (Serial.available() <= 0) {

    Serial.print(&apos;A&apos;);   // send a capital A

    delay(300);

  }
}

/* Processing sketch to run with this example:

  // This example code is in the public domain.

  import processing.serial.*;

  int bgcolor;           // Background color

  int fgcolor;           // Fill color

  Serial myPort;                       // The serial port

  int[] serialInArray = new int[3];    // Where we&apos;ll put what we receive

  int serialCount = 0;                 // A count of how many bytes we receive

  int xpos, ypos;                // Starting position of the ball

  boolean firstContact = false;        // Whether we&apos;ve heard from the microcontroller

  void setup() {

    size(256, 256);  // Stage size

    noStroke();      // No border on the next thing drawn

    // Set the starting position of the ball (middle of the stage)

    xpos = width / 2;

    ypos = height / 2;

    // Print a list of the serial ports for debugging purposes

    // if using Processing 2.1 or later, use Serial.printArray()

    println(Serial.list());

    // I know that the first port in the serial list on my Mac is always my FTDI

    // adaptor, so I open Serial.list()[0].

    // On Windows machines, this generally opens COM1.

    // Open whatever port is the one you&apos;re using.

    String portName = Serial.list()[0];

    myPort = new Serial(this, portName, 9600);

  }

  void draw() {

    background(bgcolor);

    fill(fgcolor);

    // Draw the shape

    ellipse(xpos, ypos, 20, 20);

  }

  void serialEvent(Serial myPort) {

    // read a byte from the serial port:

    int inByte = myPort.read();

    // if this is the first byte received, and it&apos;s an A, clear the serial

    // buffer and note that you&apos;ve had first contact from the microcontroller.

    // Otherwise, add the incoming byte to the array:

    if (firstContact == false) {

      if (inByte == &apos;A&apos;) {

        myPort.clear();          // clear the serial port buffer

        firstContact = true;     // you&apos;ve had first contact from the microcontroller

        myPort.write(&apos;A&apos;);       // ask for more

      }

    }

    else {

      // Add the latest byte from the serial port to array:

      serialInArray[serialCount] = inByte;

      serialCount++;

      // If we have 3 bytes:

      if (serialCount > 2 ) {

        xpos = serialInArray[0];

        ypos = serialInArray[1];

        fgcolor = serialInArray[2];

        // print the values (for debugging purposes only):

        println(xpos + "\t" + ypos + "\t" + fgcolor);

        // Send a capital A to request new sensor readings:

        myPort.write(&apos;A&apos;);

        // Reset serialCount:

        serialCount = 0;

      }

    }

  }

*/

/* Max/MSP version 5 patch to run with this example:

----------begin_max5_patcher----------

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-----------end_max5_patcher-----------

*/
[Get Code]

Processing Code

Copy the Processing sketch from the code sample above. As you change the value of the analog sensor, you'll get a ball moving onscreen something like this. The ball will appear only when you push the button:

serialCallResponse output

Max Code

The max patch looks like this. Copy the text from the code sample above.

Max5SerialCallResponse

See Also:

  • serial.begin()

  • serial.available()

  • serial.print()

  • analogRead()

  • ASCIITable - Demonstrates Arduino's advanced serial output functions.

  • Dimmer - Move the mouse to change the brightness of an LED.

  • Graph - Send data to the computer and graph it in Processing.

  • Midi - Send MIDI note messages serially.

  • MultiSerialMega - Use two of the serial ports available on the Arduino and Genuino Mega.

  • PhysicalPixel - Turn a LED on and off by sending data to your board from Processing or Max/MSP.

  • ReadASCIIString - Parse a comma-separated string of integers to fade an LED.

  • SerialCallResponseASCII - Send multiple variables using a call-and-response (handshaking) method, and ASCII-encode the values before sending.

  • SerialEvent - Demonstrates the use of SerialEvent().

  • VirtualColorMixer - Send multiple variables from Arduino to your computer and read them in Processing or Max/MSP.

Last revision 2015/07/29 by SM