CHAPTER 4: EXTERNAL LED BLINK

Now that you are familiar with how to run a basic sketch on an Arduino, lets take it up a notch. We will learn to connect an external LED to Arduino and control it via a sketch.

Things required for this chapter

Arduino Uno/Uno (Arduino compatible board)
USB Cable (Type A/B Standard USB 2.0 cable)
Bread board
1 x LED
1 x 220Ω Resistor
2 x Jumper wires

Like in the previous example, we will have to setup two parts.

Hardware setup:

Wiring LED's are the most common thing you would do in your projects. However, it has to be noted that LED's are polarized, which means if you connect +ve end of the LED to -ve end of the circuit, there is a high chance that you might burn the LED. So, how do you differ the +ve end from the -ve end?

From the image below, we can see two differentiating features which helps us to identify the +ve and the -ve terminal.

The main feature you notice is from the front view which is the difference in the length of the terminals. +ve terminal is longer then the -ve terminal.
From the Top view, we can see a flat side in the circular ring of the LED. This indicates the Cathode (-ve terminal).

Figure: Schematics of LED

Image via - Society of Robots

Next, we should connect the LED to the Arduino. Seems straight forward right? Its not. The connection is done according to the figure below.

Figure: Circuit connection for blinking an external LED

We connect a wire (Red) from Digital pin 7 of the UNO to the breadboard and connect a 220Ω resistor in series with the +ve end if the Red LED. The reason is simply to limit the current flow across it since the LED is a diode which takes in certain amount of current. The value of resistance to be used is based on the Ohm's law. Then we connect another wire (Black) from the -ve end of the LED to the ground of Arduino which is denoted as GND.

NOTE: Different color LED's have a different forward voltage. In our case, Red LED has a forward voltage of 2.0V and forward current of 20mA. To know more click here

Since the resistance value is 150Ω, we can connect a resistor of 150Ω or above. However, it has its own limitations on how large resistor you can connect. The reason I connected 220Ω resistor is because that was the closest available resistor with me since I didn't have a 150Ω resistor.

Sketch setup:

The sketch is similar to the previous sketch. Instead of lighting the internal LED, we control the external LED.

Figure: LED blink sketch

The main difference is the pin number. We are using pin 7. So we initialize pin 7 in our sketch.

Final Outcome

Here is a representation of what the Arduino will output after running the sketch on it.

Up next, Chapter 4: Controlling the brightness of an LED

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