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Serial Call and Response (handshaking) with ASCII-encoded output

This example demonstrates string-based communication from the Arduino board to the computer using a call-and-response (handshaking) method.

The sketch sends an ASCII string on startup and repeats that until it gets a serial response from the computer. Then it sends three sensor values as ASCII-encoded numbers, separated by commas and terminated by a linefeed and carriage return, and waits for another response from the computer.

You can use the Arduino 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. The examples below split the incoming string on the commas and convert the string into numbers again.

Compare this to the Serial call and response example. They are similar, in that both use a handshaking method, but this one encodes the sensor readings as strings, while the other sends them as binary values. While sending as ASCII-encoded strings takes more bytes, it means you can easily send values larger than 255 for each sensor reading. It's also easier to read in a serial terminal program.

Hardware Required

  • Arduino Board
  • (2) analog sensors (potentiometer, photocell, FSR, etc.)
  • (1) momentary switch/button
  • (3) 10K ohm resistors
  • breadboard
  • hook-up wire

Software Required

Circuit

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

click the image to enlarge

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

Schematic

click the image to enlarge

Code

/*
  Serial Call and Response in ASCII
 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 ASCII-encoded, comma-separated sensor values,
 truncated by a linefeed and carriage return,
 whenever it gets a byte in.
 
 Thanks to Greg Shakar and Scott Fitzgerald for the improvements
 
  The circuit:
 * potentiometers attached to analog inputs 0 and 1
 * pushbutton attached to digital I/O 2
 
 
 
 Created 26 Sept. 2005
 by Tom Igoe
 modified 24 Apr 2012
 by Tom Igoe and Scott Fitzgerald
 
 This example code is in the public domain.
 
 http://www.arduino.cc/en/Tutorial/SerialCallResponseASCII
 
 */


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 and wait for port to open:
  Serial.begin(9600);
  while (!Serial) {
    ; // wait for serial port to connect. Needed for Leonardo 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:
    firstSensor = analogRead(A0);
    // read second analog input:
    secondSensor = analogRead(A1);
    // read  switch, map it to 0 or 255L
    thirdSensor = map(digitalRead(2), 0, 1, 0, 255);  
    // send sensor values:
    Serial.print(firstSensor);
    Serial.print(",");
    Serial.print(secondSensor);
    Serial.print(",");
    Serial.println(thirdSensor);              
  }
}

void establishContact() {
  while (Serial.available() <= 0) {
    Serial.println("0,0,0");   // send an initial string
    delay(300);
  }
}


/*
Processing code to run with this example:

// This example code is in the public domain.

import processing.serial.*;     // import the Processing serial library
Serial myPort;                  // The serial port

float bgcolor;          // Background color
float fgcolor;          // Fill color
float xpos, ypos;           // Starting position of the ball

void setup() {
  size(640,480);

  // List all the available serial ports
  println(Serial.list());

  // I know that the first port in the serial list on my mac
  // is always my  Arduino module, so I open Serial.list()[0].
  // Change the 0 to the appropriate number of the serial port
  // that your microcontroller is attached to.
  myPort = new Serial(this, Serial.list()[0], 9600);

  // read bytes into a buffer until you get a linefeed (ASCII 10):
  myPort.bufferUntil('\n');
 
  // draw with smooth edges:
  smooth();
}

void draw() {
  background(bgcolor);
  fill(fgcolor);
  // Draw the shape
  ellipse(xpos, ypos, 20, 20);
}

// serialEvent  method is run automatically by the Processing applet
// whenever the buffer reaches the  byte value set in the bufferUntil()
// method in the setup():

void serialEvent(Serial myPort) {
  // read the serial buffer:
  String myString = myPort.readStringUntil('\n');
  // if you got any bytes other than the linefeed:
    myString = trim(myString);
 
    // split the string at the commas
    // and convert the sections into integers:
    int sensors[] = int(split(myString, ','));

    // print out the values you got:
    for (int sensorNum = 0; sensorNum < sensors.length; sensorNum++) {
      print("Sensor " + sensorNum + ": " + sensors[sensorNum] + "\t");
    }
    // add a linefeed after all the sensor values are printed:
    println();
    if (sensors.length > 1) {
      xpos = map(sensors[0], 0,1023,0,width);
      ypos = map(sensors[1], 0,1023,0,height);
      fgcolor = sensors[2];
    }
    // send a byte to ask for more data:
    myPort.write("A");
  }

*/


/*

Max/MSP version 5 patch to run with this example:
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-----------end_max5_patcher-----------

*/

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. When you turn the switch off, the ball will disappear:

Max Code

The max patch looks like this. Copy the text from the code sample above and paste it into a new Max window

See Also:

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