How to use a virtual pin

Would you rather watch than read? Here's the video version of this article.

Virtual pins

To learn the basics of Blynk's virtual pins, let's work on a small project.

We will use a virtual pin in Blynk to send a PWM value to the LED connected to digital pin 2 (D2) on the Arduino Nano. This pin is PWM capable.

First, let's look at the relevant documentation. Blynk publishes its documentation at docs.blynk.cc. Keep this site open for quick reference.

On the left side is the table of contents.

Scroll down to "Blynk Main Operations" and click on "Virtual Pins".

That will take you to the relevant section in this documentation, which is recommended reading.

The BLYNK_WRITE function

To get a virtual pin in Blynk to do anything you want it to do, first, you need to add the BLYNK_WRITE block in your sketch and assign it to the virtual pin you want to use to control this segment.

Then, inside that block, you can put whatever code you want.

The BLYNK_WRITE function can pass a value (such as a number) sent from the application on your phone to your sketch as a parameter. You can get that value using the param variable. Once you have the value, you can convert it into an integer, and then store it in a local or global variable.

From that point, you can do whatever you want with this information - with this number, in this case. 

The led_pwm function

You can see my sketch in the image below.

You can also see it in the course's Github repository.

The way that I have implemented this in my sketch is to take the sketch as we left it in the previous article (I have simply changed its name; I call it "Blynk_Arduino_Nano33IoT.ino" so that it's easy for me to identify it), and I have added a new function called led_pwm, which receives a pwm_value, an integer.

The function uses analogWrite to write that value to digital pin 2 (stored in the pwm_pin variable).

The picture below is showing how I have implemented the virtual pin functionality.

I used the BLYNK_WRITE function.

I pass the virtual pin that I want to use to control the segment in this part of the code. The Blynk application will send a value, which I capture using the param variable, converted it into an integer, and then pass it on to the led_pwm function.

The Slider

Upload the sketch, and while that is happening, go over to my Blynk application, stop it, and add a new widget, the slider.

Place it a bit further down and extend it to the full width.

Now, tap the slider to go into its settings.

For the pin setting, use Virtual 1 (V1) since you set the BLYNK_WRITE function to receive data from Virtual pin 1 (V1) earlier.

You can give the widget a name if you want; say "PWM".

You can keep the default configuration for the PWM function on the Arduino Nano 33 IoT, which is 8 bits.

An 8-bit PWM value has a range from 0 to 255.

I also want to be able to see the value changing as I am sliding the slider left and right, so, I'm will switch off the "Send Values On Release Only" toggle switch. I want values to be sent constantly, as I'm changing them.

Next, tap "OK" and tap on the play button.

We can now try this out.

Slide the PWM widget handle up. You can see that the LED is becoming brighter 

Even though I have connected two widgets to the same physical pin, both widgets still work.

There's some delay between the time I press on the button or move the slider and when the LED reacts because I am using the Blynk cloud server. It takes a bit of time for the update to reach the public server and come back. One of the main advantages of having a local private server is that the lag is minimal. 

As you can see with virtual pins, you can do anything you want without having to worry about the physical limitations of whichever model device you have chosen. 

Conclusion

In the next guide article, I will show you how to reuse the simple Blynk project we built and replace the Arduino Nano 33 IoT with an ESP32.

You will do that by making a few very simple changes to the Blynk project itself. And, of course, we have to upload the appropriate sketch of the ESP32.

Go ahead and read the next page.