Arduino Uno: Blink an LED (3)

An example of a simple Arduino program to blink an LED connected to a digital pin (e.g., pin 13)

 

1. Connect a LED (+lead) to pin 13 and (-lead) to GND. Negative lead is usually the shorter lead. 

2. Add the following to the definitions area of your sketch: above void setup ( )

 

※ Remember, the comments help you and otehrs understand the code.

• “int” : we are defining a data type.
• We are telling the Arduino to let a variable called “led” represent an integer
• Anytime “led” is used in the code, Arduino sees 13
  Ex. 12 + led = 25
• There are many more data types

3. Add the following to the your sketch in void setup ( )

 

• One use of void setup( ) is to assign pins
• We do this using the function pinMode(pin, mode)
  - “pin” refers to a specific pin on the Arduino you are wanting to use (in our case pin 13 aka “led”)
  - “mode” is either INPUT or OUTPUT
  - OUTPUT sets up the pin so it can give outputs
  - INPUT sets up the pin so it can receive inputs
• pinMode(led, OUTPUT): Pin 13 is now an output

4. Add the following to your sketch in void loop ( )

void loop ( ) ....

• Runs once void setup is finished.
• Loops through the cod within forever.

digitalWrite(pin, value)

• "pin" is whichever pin your are writing to
• "value" can be either HIGH or LOW
• HIGH means the pin is at 5V - "on"
• LOW means the  pin is at 0V - "off"

delay(time)

Tells the Arduino to wait a specific amount of time (in milliseconds) before going to the next line of code.

Ex) 1000 ▶ 1000 ms = 1 sec.

 

5. Compile (#1) cod and check for messages.

6. Upload (#2) code to Arduino

Does a LED blink?

Exercise) Change the delay in teh sketch and try again. Ex) delay time: 500

• Do you see a change?

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Remove the LED from PIN 13 and GND

• Another LED on the board should start blinking
• The "L" on the Uno stands for LED
• Do you see this?

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Say you wanted to blink an LED on Pin 9, what would you change in the code?

        int LED = 9;

• Could you connect LED directly to Pin 9 ang GND like for Pin 13?
• No (OK for a few seconds) but why?
• LED requires some current limiting (resistor)
• Let's look at Pin 13 on the schematic

Pin 13 on the Schematic

Follow the line and find a built in 1 kΩ resistor. 

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Breadboard

• Columns connected.
• Rows connected on power rails.
• Columns on one side not connected to columns on other side.
• Breadboard has power and ground rails
• Individual points on rails (rows) are connected
• One rail and its points are independent of other rails.

• Also has numbers and letters to coordinate builds

• So if we use any otehr pin to light up an LED, we need to add a resistor (1 kΩ)