Examples > Communication

Physical Pixel

This example uses the MSP430 Launchpad to receive data from the computer. The Launchpad turns on an LED when it receives the character ‘H’, and turns off the LED when it receives the character ‘L’. The data can be sent from the Energia serial monitor, or another program like Processing (see code below).

Hardware Required

  • MSP-EXP430G2 LaunchPad
  • LED [on-board as part of the LaunchPad]

Relevant Groundwork

For this example, it is easier to use the built-in LED on the LaunchPad corresponding to Pin 2 for Red or Pin 14 for Green. You can attach an LED externally to pin 9 on the Launchpad where the long leg, or anode, goes to pin 9. The short leg, or cathode, goes to ground.

Circuit

PhysicalPixel_bb

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

PhysicalPixel_schem

Code Explanation

Energia

The LaunchPad will look for ASCII characters that will be sent from the Energia Serial Monitor in order to turn an LED on the LaunchPad board on (High) or off (Low). When an ‘H’ is written in the Serial Monitor, the LED will turn on, when an ‘L’ is written into the monitor, the LED will turn off. We begin by initializing a constant (in this code ledPin) to the value of 14 or the pin associated with the Green LED on the LaunchPad board. We also need a new variable called incomingByte that will save the ASCII character read by the Serial Monitor.

In the setup() section, we initialize Serial communication and set the pin associated to the Green LED (Pin 14) as an output.

In the loop() section, the Serial.available() will look for characters read from the Serial Monitor. This is inside an if statement that will continuously run while the Serial is available. We set our variable incomingByte to what is being read from the Serial Monitor. There are 2 if statements that follow. The first controls what will happen when an ‘H’ is read in the Serial Monitor. If an ‘H’ is received, it will set the Green LED High using the digitalWrite() function. The second if statement controls what happens when an ‘L’ is received. Very similar to the previous statement, only difference is when ‘L’ is seen, the LED goes Low.

Processing

The Processing code will send data to the COM port to control what happens to the LED. The Processing code generates a window that has a grey box inside surrounded by a blackbackground. When you place your mouse cursor into the grey box, Processing will send ‘H’ to the port enabling the Green LED to go high. When the cursor is not in the grey box, Processing will send ‘L’ to the port turning the LED low.

Code

/*
  Physical Pixel

  An example of using the Launchpad to receive data from the 
  computer. In this case, the Launchpad turns on an LED when
  it receives the character 'H', and turns off the LED when it
  receives the character 'L'.

  The data can be sent from the Energia serial monitor, or another
  program like Processing.

  The circuit:
  * LED connected from digital pin 14 to ground

  created 2006
  by David A. Mellis
  modified 30 Aug 2011
  by Tom Igoe and Scott Fitzgerald
  Modified 15 April 2013
  By Sean Alvarado

  This example code is in the public domain.

*/

const int ledPin = 14; // the pin that the Green LED that is    attached to on Launchpad 
int incomingByte; // a variable to read incoming serial data into

void setup() {
  // initialize serial communication:
  Serial.begin(9600);
  // initialize the LED pin as an output:
  pinMode(ledPin, OUTPUT);
}

void loop() {
  // see if there's incoming serial data:
  if (Serial.available() > 0) {
    // read the oldest byte in the serial buffer:
    incomingByte = Serial.read();
    // if it's a capital H (ASCII 72), turn on the LED:
    if (incomingByte == 'H') {
      digitalWrite(ledPin, HIGH);
    } 
    // if it's an L (ASCII 76) turn off the LED:
    if (incomingByte == 'L') {
      digitalWrite(ledPin, LOW);
    }
  }
}

/* Processing code for this example

// mouseover serial 

// Demonstrates how to send data to the Launchpad I/O board, in order to 
// turn ON a light if the mouse is over a square and turn it off 
// if the mouse is not. 

// created 2003-4
// based on examples by Casey Reas and Hernando Barragan
// modified 30 Aug 2011
// by Tom Igoe
// modified 15 April 2013
// by Sean Alvarado
// This example code is in the public domain.

import processing.serial.*; 

float boxX;
float boxY;
int boxSize = 20;
boolean mouseOverBox = false;

Serial port; 

void setup() {
  size(200, 200);
  boxX = width/2.0;
  boxY = height/2.0;
  rectMode(RADIUS); 

  // List all the available serial ports in the output pane. 
  // You will need to choose the port that the Launchpad is 
  // connected to from this list. The first port in the list is 
  // port #0 and the third port in the list is port #2. 
  println(Serial.list()); 

  // Open the port that the Launchpad is connected to (in this case #0) 
  // Make sure to open the port at the same speed Energia is using (9600bps) 
  port = new Serial(this, Serial.list()[0], 9600); // In the [] you will place the number corresponding to the COM your LaunchPad is connected to

}

void draw() { 
  background(0);

  // Test if the cursor is over the box 
  if (mouseX > boxX-boxSize && mouseX < boxX+boxSize && mouseY > boxY-boxSize && mouseY < boxY+boxSize) {
    mouseOverBox = true; 
    // draw a line around the box and change its color:
    stroke(255); 
    fill(153);
    // send an 'H' to indicate mouse is over square:
    port.write('H'); 
  } 
  else {
    // return the box to its inactive state:
    stroke(153);
    fill(153);
    // send an 'L' to turn the LED off: 
    port.write('L'); 
    mouseOverBox = false;
  }

  // Draw the box
  rect(boxX, boxY, boxSize, boxSize);
}

*/

Working Video

Try it out:

See Also:

Getting Started Home