Control of LED

I tried to connect arduino with blynk.Every step I followed correctly but I couldn’t able to control the LED with my mobile.Please help me with this

Help US by telling us EVERYTHING. We can’t help if we don’t know anything about your system.

What information do you need about my system?.I am ready to provide

You said “mobile” - Android or iOS?

You said Arduino - which Arduino?

Which IDE including version number?

How you are trying to connect your Arduino to the internet (USB, Ethernet, WiFi Shield, ESP as shield, BLE, fresh-air)?

Whichever method please provide precise details of the hardware i.e. model number of shield (some are rubbish) or ESP version (1, 3 7, 12, 12E etc).

Which sketches have you tried?

Did you download the 4 “Blynk” libraries and manually install them in the correct place as per the instructions?

What PC are you using incl OS?

What have you tried, what results did you get (Serial Monitor output / screenshots etc) and what results did you expect?

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Have you read the comprehensive documentation 2 or 3 times at

1 Like

my mobile is android
I have read the documentation and followed all the steps aptly
I use Arduino UNO
I have downloaded the blynk libraries too.
I hav even run the batch file and it displayed connection to blynk cloud, displayed the same details as mentioned in the documentation
I used usb serial connection type
my os windows 8.1
When i tried to open the serial moniter it diplayed the error that com3 is currently in use

Paste your precise sketch (remove token) and ensure it is formatted with the </> button.

IDE and version?


  • Blynk is a platform with iOS and Android apps to control
  • Arduino, Raspberry Pi and the likes over the Internet.
  • You can easily build graphic interfaces for all your
  • projects by simply dragging and dropping widgets.
  • Downloads, docs, tutorials:
  • Blynk community:
  • Social networks:
  • Blynk library is licensed under MIT license
  • This example code is in public domain.

  • This example shows how to use ordinary Arduino Serial
  • to connect your project to Blynk.
  • Feel free to apply it to any other example. It’s simple!

  •        USB HOWTO:


// You could use a spare Hardware Serial on boards that have it (like Mega)
#include <SoftwareSerial.h>
SoftwareSerial DebugSerial(2, 3); // RX, TX

#define BLYNK_PRINT DebugSerial
#include <BlynkSimpleStream.h>

// You should get Auth Token in the Blynk App.
// Go to the Project Settings (nut icon).
char auth[] = “</>”;

void setup()
// Debug console

// Blynk will work through Serial
Blynk.begin(auth, Serial);

void loop()

@vigneshjm Hi, If you COM3 is in used you can change manually by doing this steps.

  • Brows your computer, find the “computer icon” named Computer or This computer then right click on it, select “manage” or from your search box type in “computer management”
    under computer management find the “device manager” after clicking device manager you can see from the right side pane the “ports (com & lpt)” Take note you should plug your usb arduino device otherwise this option will not appear from list options. click this > symbol from the ports to see the list devices attached in your pc, you see the arduino device from there right click then select the properties, another small window will open select the “port settings” tab click the advance button and then put your any port number you wish, in used port also u can re map once port number is assigned just click ok. ok then exit. that’s it.

For LED controlling actually no much sketch i required, you just simply identify the PWM in digital pins from your arduiono board then map it to your Blynk apps slider widget that’s it you have instant control.
and if you want to control high current led load you have to buy like pwm led driver, 12vdc or 24vdc led driver. take note. pwm pins cannot handle large current load, and voltage output is only 4.99.
please send your code or sketch so we can review to help you out.

put this put this symbol ``` 3timesbefore and after your code before posting.