You are now ready to build your first Blynk application that can be used to control an LED attached to the Raspberry Pi from your smartphone or tablet. The application consists of the following components:

• Blynk app running on your smartphone or tablet
• C++ project running on Raspberry Pi
• Blynk cloud

You will need following things to build the circuit:

• Raspberry Pi 3 board
• A breadboard
• An LED - Basic Red 5 mm (https://www.sparkfun.com/products/9590)
• A 330 Ohm 1/6 Watt PTH resistor (https://www.sparkfun.com/products/11507) color coded orange, brown, gold
• Two male-female jumper wires

In this example, you will learn how to build a Blynk application to turn an LED on and off.

To start building a project, tap Create New Project in the center of the screen. This will bring you to the Create New Project wizard. You will walk through this wizard step by step.

Follow these steps to complete the Create New Project:

1. Tap New Project:

2. On the Create New Project page, type LED Controller in the Project Name textbox:

3. Tap CHOOSE DEVICE to get the available hardware models and tap Raspberry Pi 3 B from the list. After choosing the hardware model, tap OK.

4. Tap...

These steps will show you how to add a Button widget to your project, which is a controller widget that can be used to turn an LED on and off.

The working area of the app builder is referred to as a canvas and has a dotted background with horizontal and vertical guides that allow you to easily arrange and align different types of widgets:

1. Tap anywhere on the canvas or the plus icon on the toolbar to get the Widget Box. The Widget Box lists all the widgets available under different categories to build the application.
2. On the Widget Box, tap Button under CONTROLLERS:

3. A Button widget will be added onto the canvas:

4. Tap the Button widget to open the Button Settings page.
5. Tap PIN under OUTPUT and choose Digital followed by GP18 PWM from the list (this is the physical Pin 10/BCM Pin 18/GPIO Pin 18 in...

Now, you're ready to run your first Blynk project:

1. Log in to your Raspberry Pi using the SSH protocol with PuTTY (see Chapter 1, Setting Up a Development Environment, for information on logging in to your Raspberry Pi with PuTTY).
2. Change to the blynk-library/linux directory by issuing this command:

pi@raspberrypi:~ $cd blynk-library/linux

3. Run the following command with the auth token associated with your project:

pi@raspberrypi:~/blynk-library/linux $ sudo ./blynk --token=ca7bed1c92214503a65de8e20164994f

4. The terminal will show an output similar to this:

[0]

___ __ __

/ _ )/ /_ _____ / /__

/ _ / / // / _ / '_/

/____/_/_, /_//_/_/_

/___/ v0.5.0 on Linux

[1] Connecting to blynk-cloud.com:8442

[3490] Ready (ping71ms).

Now, your Raspberry Pi is successfully connected with the Blynk cloud at https://www.blynk.cc/. The following steps show you how to use the app to control the LED attached to GPIO pin 18:

1. Tap the Play button on the toolbar:

2. This will switch you from edit mode to play mode, where you can interact with the hardware. The play button is replaced with a Stop button that allows you to go back to edit mode:

3. You can tap the chip icon (the icon like a microprocessor) to see the device status, whether it is online or offline. The following screenshot show that the Raspberry Pi is online:

4. If your Raspberry Pi is offline, the notification looks as shown in the following screenshot. There are several reasons it can go offline. Some of them are:
   • Lost internet...

Now you know how to write the current state of the Button widget to a GPIO pin.

With virtual pins, you can send or receive any type of data between the microcontroller (Raspberry Pi) and the Blynk app. The Blynk app builder provides 128 virtual pins for working with Raspberry Pi. They allow you to interface with sensors, actuators, and libraries. These pins have no physical properties. Some Blynk widgets support virtual pins, some do not.

As an example, you can write the current state of the Button widget to the virtual pin V1 as shown here. Then, you can assign the incoming value from the virtual pin to a variable for further processing:

BLYNK_WRITE(V1)

{

intpinValue = param.asInt(); // assigning value on Virtual Pin (V1) to a variable

// process received value

}

In this section, you will modify the Blynk app, LED Controller, by configuring a virtual pin:

1. Go to edit mode by tapping the stop icon if you're already in play mode.
2. Tap the Button widget.
3. On the Button Settings page, tap GP 18 under OUTPUT. Scroll down and choose Virtual from the left-hand part of the list. Then, scroll down and choose V1 from the right-hand part of the list under PIN. Blynk provides 128 virtual pins for working with Raspberry Pi. Finally, tap OK.

4. Now, your Button Settings page should look like this:

5. Tap the LEFT arrow on the toolbar. You will see the new button configured with the virtual pin V1:

Now, you've successfully modified the Button widget, so it can write values to the virtual pin V1.

To complete your application, the main.cpp file should also be modified to process the data on the virtual pin. These steps show you how to modify it with the nano editor:

1. Open the main.cpp file with nano by issuing the following command:

pi@raspberrypi:~/blynk-library/linux $ sudonanomain.cpp

2. Before using the WiringPi GPIO library, you need to include its header file in your program as follows:

#include <wiringPi.h>

3. Scroll down to the file with the arrow keys on your keyboard and add the following code to the setup() function:

void setup()
{
Blynk.begin(auth, serv, port);
pinMode(1, OUTPUT);
}

The pinMode() function allows you to set the mode of a pin to either INPUT, OUTPUT, or PWM_OUTPUT. Note that only WiringPi pin 1 (BCM_GPIO 18) supports PWM output.

4. Then, add the following lines to the BLYNK_WRITE(V1...

Let's see how to run the project:

1. After building the project, run it with this command:

pi@raspberrypi:~/blynk-library/linux $sudo ./blynk --token=ca7bed1c92214503a65de8e20164994f

2. You should get an output that looks like this:

3. Tap the Play button on the toolbar. Now, you can turn on and off the LED by tapping the button. When you tap the button, the console will output the current value on the virtual pin V1.
4. The following screenshot shows the console output when you tap the Button widget:

You have learned a lot and built your very first complete Blynk application, which consists of a Blynk hardware and a Blynk app to control an LED attached to the Raspberry Pi over Wi-Fi from a smartphone or a tablet. Now you know how to add the Button widget and configure it to work with the physical pins of the hardware, as well as with virtual pins. You also know how to write code in C++ to process the values on the virtual pin for the Button widget.

In Chapter 3, Using Controller Widgets, you will learn in detail about all the available controller widgets that can be found in the Blynk app builder.