LilyPad Development Board Activity Guide

Contributors: Gella

8: LED Bar Graph

The LilyPad Development Board includes five pre-wired white LEDs, because they're in a row they're perfect for creating a LED bar graphs. In this activity, we'll experiment with graphing the readings from the light sensor onto the row of LEDs.

LilyPad Boards Used in This Activity

• LilyPad Arduino Simple
• LilyPad Light Sensor
• LilyPad LEDs

New Concepts Introduced in This Activity

Using Arrays

Arrays are a handy way to store many variables in one structure. Here we'll store the pin / sew tab numbers of the white LEDs, making them easier to use as a group.

Creating Custom Functions

So far we've been using Arduino's built-in functions, but you can also create your own. Functions are great for bits of code you want to run repeatedly, or even reuse in other programs.

Incrementing Shortcuts

Many times in programming you'll want to add or subtract one from a number, such as in a for() loop. In earlier activities, we did this with the pattern x = x + 1. But there are some handy shortcuts you can use:

Learn more about compound operators for shorcuts and their use at the Arduino Reference site.

Example Code

To open the code, go to:

File > Examples > LilyPadDevelopmentBoard_ActivityGuide > LPD_08_BarGraph

You can also copy and paste the following code into the Arduino IDE. Hit upload, and see what happens!

language:c
/*
LilyPad Development Board Activity 8: LED Bar Graph
SparkFun Electronics
https://www.sparkfun.com/products/11262

Play with the row of five LEDs on the bottom of the LilyPad Development Board

Follow the tutorial at: 
https://learn.sparkfun.com/tutorials/lilypad-development-board-activity-guide/8-led-bar-graph

This code is released under the MIT License (http://opensource.org/licenses/MIT)

******************************************************************************/

// Create a variable for the light sensor input:

int sensorPin = A6;


// To the five LEDs on the LilyPad Development Board easier to use, we'll put those numbers into an array.
// The initial [5] defines the size of the array (five elements).
// We're filling the array with predefined values, but you could do this
// in your code as well.

int bargraphLED[5] = {5,6,A2,A4,A3};

// The array is indexed from 0 to 4; for example bargraphLED[2] = A2

void setup()
{
  int x;

  // Initialize the sensor pin as an input, but without a pullup
  // (Pullups are only used for switch inputs)

  pinMode(sensorPin, INPUT);

  // Initialize the bargraph LED pins as outputs
  // We'll use the matrix we defined above,
  // where the LEDs are indexed from 0 to 4

  for (x = 0; x <= 4; x++)
  {
    pinMode(bargraphLED[x], OUTPUT);
  }

  // Initialize the serial monitor

  Serial.begin(9600);
}

void loop()
{
  int sensorValue;

  // Read the sensor value (will be 0 to 1023):

  sensorValue = analogRead(sensorPin);

  // Print out the sensor reading:

  Serial.print("sensor value: ");
  Serial.println(sensorValue);

  // Display the sensor reading on the bar graph LEDs.
  // This is a new function that we created ourselves (see below).

  barGraph(sensorValue);
}

// Here we're making our own command called barGraph:
// The first "void" means we don't return anything from this command
// The "int value" is what we'll pass to the command (it must be an integer,
// and it will be called "value" in the command.

void barGraph(int value)
{
  // Create a LED bargraph using value as an input.
  // Value should be in the range 0 to 1023.

  int x;

  // Step through the bargraph LEDs,
  // Turn them on or off depending on value.

  // Value will be in the range 0 to 1023.
  // There are 6 LEDs in the bargraph.
  // 1023 divided by 5 is 204, so 204 will be our threshold
  // between each LED

  for (x=0; x <= 4; x++)
  {
    if (value > (x*204) )
    {
      digitalWrite(bargraphLED[x], HIGH);
    }
    else
    {
      digitalWrite(bargraphLED[x], LOW);
    }    
  }
}

What You Should See

After the code loads, the row of white LEDs on the LilyPad Development Board will create a bar graphing showing how much light is hitting the light sensor by lighting up more or less of the row. Try covering the sensor with your hand, or aiming a flashlight at it to see a larger or smaller response from the bar graph.

Understanding Your Program

Program Overview

1. Set up an array with the white LED pins.
2. Configure the pins and serial monitor.
3. Read the light level.
4. Display it on the bar graph.
5. Repeat.

Code to Note

Coding Challenges

• Alter the function of the bar graph so that all of the LEDs are on, and go out as the value increases.

• Alter the value of the bar graph so that it fills in from the right rather than from the left. Hint: Can you do this by declaring the array differently?