LED Array Circuit

Blink and Current Limiting Resistors

In lab this week we got started with the Sparkfun kit and hopefully you all got acquainted the Sparkfun RedBoard (a.k.a. the Arduino Uno).

I believe that all the groups working with the board got the Blink program to work and were able to "blink" the on-board blue LED that is connected to Pin 13. Some groups were able to progress to setting up multiple LED's on the breadboard.

I noticed that some groups were doing this without using a current limiting resistor. Hooking up the LED without the resistor results in a maximum current from the I/O pin and this situation can end up "killing" the pin and can also burn out the whole ATmega328 chip.

You can read about this on the web - google "arduino max current", here is a summary...

LED Array and other circuits

I would encourage those of you with kits to go ahead and explore the kit and create a bunch of the test circuits. I would also like to share a couple circuits and sketches with you.

The first of these is and LED array. The following images show both the actual circuit on the breadboard and then three diagrams of the same circuit that I created using the Fritzing utility.

LED Array setup on Sparkfun breadboard

Diagram of circuit created using Fritzing

Schematic of circuit created using Fritzing

PCB layout for LED Array using Fritzing

Code samples

If you construct this circuit you can use it to run a number of test programs that you can use to explore some elements of C coding.

The Arduino sketches are below.

BlinkTwo - as the name implies, this program demonstrates how to set the sketch to blink two LEDs in unison.

	/*
	BlinkTwo
	Turns two LEDs on and off in unison.
	The delay times are controlled by two variables
	that are defined at the beginning of the program.
	This example code is in the public domain.
	*/
	// Use the LEDs that are connected to I/O pins 12 and 13
	int led1 = 12;
	int led2 = 13;
	// Set delay values for the amount of time the LEDs
	// are on and the amount of time they are off.
	int onTime = 100;
	int offTime = 250;
	// the setup routine runs once when you press reset:
	void setup() {
	// initialize the digital pins as outputs.
	pinMode(led1, OUTPUT);
	pinMode(led2, OUTPUT);
	}
	// the loop routine runs over and over again forever:
	void loop() {
	digitalWrite(led1, HIGH); // turn the LED on
	digitalWrite(led2, HIGH);
	delay(onTime); // wait for a bit
	digitalWrite(led1, LOW); // turn the LED off
	digitalWrite(led2, LOW);
	delay(offTime); // wait for a bit
	}

view raw BlinkTwo hosted with ❤ by GitHub

BlinkTwoAlternate - as the name implies, this program demonstrates how to set the sketch to blink two LEDs in an alternating pattern.

	/*
	BlinkTwo
	Turns two LEDs on and off in unison.
	The delay times are controlled by two variables that are defined at the
	beginning of the program.
	This example code is in the public domain.
	*/
	// Use the LEDs that are connected to I/O pins 12 and 13
	int led1 = 12;
	int led2 = 13;
	// Set delay values for the amount of time the LEDs are on and the amount of time they are off.
	int onTime = 100;
	int offTime = 250;
	// the setup routine runs once when you press reset:
	void setup() {
	// initialize the digital pins as outputs.
	pinMode(led1, OUTPUT);
	pinMode(led2, OUTPUT);
	}
	// the loop routine runs over and over again forever:
	void loop() {
	digitalWrite(led1, HIGH); // turn the LED on (HIGH is the voltage level)
	delay(onTime); // wait for a bit
	digitalWrite(led1, LOW); // turn the LED off by making the voltage LOW
	delay(offTime); // wait for a bit
	digitalWrite(led2, HIGH); // turn the LED on (HIGH is the voltage level)
	delay(onTime); // wait for a bit
	digitalWrite(led2, LOW); // turn the LED off by making the voltage LOW
	delay(offTime);
	}

view raw BlinkTwoAlternate hosted with ❤ by GitHub

LEDarray - this sketch uses the C array construct to simplify the process of setting up and running multiple LEDs. This code also introduces the use of the For Loop and IF and IF-Else constructs. Use this program o create the Knight-Rider effect.

	/*
	BlinkArray
	Usses and Array structure and For and If loops to create an LED chase effect
	This example code is in the public domain.
	*/
	/* Intialize an array of LED pins
	Define a delay called "rate"
	Define a multiple of the delay "pause" to be used after one pass through
	array
	*/
	int ledArray[] = {9, 10, 11, 12, 13};
	int rate = 50;
	int pause = 1;
	/* Use a For Loop to set the LED array pins to output
	The counter i is a local variable within the setup function
	*/
	void setup() {
	for (int i=0; i<5; i++){
	pinMode(ledArray[i], OUTPUT);
	}
	}
	/* Use a For loop to blink each LED in the array.
	The If-Else statment checks to see if the fifth LED has been
	blinked and then sets a longer delay as defined by the integer "pause."
	*/
	void loop() {
	/* Use a For loop to blink each LED in the array.
	The If-Else statment checks to see if the fifth LED has been
	blinked and then sets a longer delay as defined by the integer "pause."
	*/
	for (int i=0; i<5; i++){
	digitalWrite(ledArray[i], HIGH);
	delay(rate);
	digitalWrite(ledArray[i], LOW);
	if (i == 4) delay(pause*rate);
	else delay(rate);
	}
	/* Use a variation of the previous For Loop to race the LED's backwards.
	If "pause" is set to 1 then the LEDs create the Knight Rider effect.
	*/
	for (int j=1; j<4; j++){
	int k = 4-j;
	digitalWrite(ledArray[k], HIGH);
	delay(rate);
	digitalWrite(ledArray[k], LOW);
	delay(rate);
	}
	}

view raw Knight Rider hosted with ❤ by GitHub