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Button

The button is made to turn something on and off on your device. However, it can do more. There are different types of buttons, but most of the settings are self-explanatory. This document only covers unique settings.

Mode

Button can operate in these modes:

  1. Push. Set to ON state when pressed, then back to OFF state when released

  2. Switch. Toggles between ON/OFF state each time it is pressed

  3. Page. Opens a specified app page when pressed (requires PRO plan)

  4. QR. Opens phone QR Scanner (requires PRO plan)

How the QR code scanner works

End users will tap on the widget and a code scanner (camera) will open. The camera should be pointed to the code.

Once the code is successfully scanned, its contents will be sent to the hardware in a String format to the specified Datastream. The scanner screen will be closed automatically. A String Datastream should be added to the Device Template to accept these values.

Value of the code is sent as is (not pre-processed or post-processed by Blynk).

In case of scanning an unsupported format, no error will be shown. User would need to close the scanner view (camera) manually.

End-users would need to grant permissions to use the camera on the smartphone OS level. If permission wasn’t granted, a message will be shown to go to settings to enable access to the camera.

Scanner works with these code formats

  • QR

  • AZTEC

  • CODE_39

  • CODE_39 mod 43

  • CODE_93

  • CODE_128

  • DATA_MATRIX

  • EAN_8

  • EAN-13

  • ITF

  • PDF_417

  • UPC_E

Android app can additionally support these formats:

  • CODABAR

  • MAXICODE

  • RSS_14

  • RSS_EXPANDED

  • UPC_A

  • UPC_EAN_EXTENSION

Datastream

Select or create a datastream of data type integer, double, or string. Widget properties (label, color, etc.) are also changed via the datastream, but only for virtual, enumerable, and location pins, not digital and analog pins.

How to process button input on the device

When button is pressed, value is sent and stored into the Blynk.Cloud. After that it's sent to your device.

Reading the button value

For example, if Button Widget is set to Datastream with Virtual Pin V1, you can use such code:

BLYNK_WRITE(V1) // this command is listening when something is written to V1
{
  int pinValue = param.asInt(); // assigning incoming value from pin V1 to a variable
  
  if (pinValue == 1){
   // do something when button is pressed;
  } else if (pinValue == 0) {
   // do something when button is released;
  }
  
  Serial.print("V1 button value is: "); // printing value to serial monitor
  Serial.println(pinValue);
}

Changing button state

You can set the state of the button by updating the assigned datastream value using the hardware or HTTP API. When the widget option ‘Use datastream’s Min/Max’ is enabled, then you set the datastream to the value assigned to the datastream max in order to set the button state to ON, and set it to the datastream min value to set the Button state OFF. When the widget option ‘Use datastream’s Min/Max’ is disabled, then you specify the values to use for the OFF/ON states.

Hardware:

Blynk.virtualWrite(vPin, 1);	// best practice
// OR
Blynk.virtualWrite(vPin, HIGH);
// OR
Blynk.virtualWrite(vPin, TRUE);

HTTP API:

https://{server_address}/external/api/update/?token={your 32 char token}&V0=1

https://{server_address}/external/api/batch/update/?token={your 32 char token}&V0=1

Don't put Blynk.virtualWrite()into the void loop() as it can cause a flood of messages and your hardware will be disconnected. Send such updates only when necessary, use flags, or timers.

Sketch: Basic Sketch

Sketch: Physical Button Interrupt

Sketch: Physical Button Poll

Sketch: Physical Button State Sync

Change Button Properties

You can change certain properties of the Widget from your hardware. For that, use this command: 

Blynk.setProperty(vPin, "widgetProperty", "propertyValue");

Where:

  • vPin is: virtual pin number the widget is assigned to

  • widgetProperty: property you want to change

  • propertyValue: value of the property you want to change

Don't put Blynk.setProperty()into the void loop() as it can cause a flood of messages and your hardware will be disconnected. Send such updates only when necessary, or use timers.

Properties you can change

You can change the properties onLabel, offLabel, label, color, isDisabled, isHidden, and page of the widget from your hardware, or via an HTTP API. The URL must be encoded, so spaces in labels must be replaced with %20, and color hexadecimal values in the HTTP API URL must include the hash # character urlencoded as %23.

Change On/Off labels

Blynk.setProperty(V1, "onLabel", "ON");
Blynk.setProperty(V1, "offLabel", "OFF");

Change Widget Label

Blynk.setProperty(V1, "label", "Air temperature");

Set Button Color

//#D3435C - Blynk RED 
Blynk.setProperty(V1, "color", "#D3435C");

Disable/Enable

Widget will be greyed out on UI and users won't be able to tap on it.

Blynk.setProperty(V1, "isDisabled", true);

Show/Hide

Widget will be hidden from dashboard. Design your UI so that it doesn't look weird when there is no widget.

Blynk.setProperty(V1, "isHidden", true);

Change Page Target

This command will set which page should open when the button is pressed. PageId can be found in the mobile app in developer mode: Toolbox -> Pages

Blynk.setProperty(V1, "page", "pageId");

Change widget properties via HTTPs API

Updates the Datastream Property and all assigned Widgets

GET https://{server_address}/external/api/update/property?token={your 32 char token}&pin={your vPin}&{property}={value}

The endpoint allows you to update the Datastream Property value via GET request. All widgets (both web and mobile) that are assigned to this datastream will inherit this property. The Datastream Property is persistent and will be stored forever until you change it with another value. In order to clear the property you need to clear the device data in device actions menu.

Example: https://blynk.cloud/external/api/update/property?token=GVki9IC70vb3IqvsV0YD3el4y0OpneL1&pin=V2&label=My%20Label

https://blynk.cloud/external/api/update/property?token=GVki9IC70vb3IqvsV0YD3el4y0OpneL1&pin=V1&color=%23D3435C

https://blynk.cloud/external/api/update/property?token=GVki9IC70vb3IqvsV0YD3el4y0OpneL1&pin=V1&isDisabled=true

https://blynk.cloud/external/api/update/property?token=GVki9IC70vb3IqvsV0YD3el4y0OpneL1&pin=V1&page={pageID}

Path Parameters

Name
Type
Description

{server address}*

string

Get from the bottom right of your Blynk console. More information.

Query Parameters

Name
Type
Description

token*

string

Device auth token from Device info

pin*

string

The datastream virtual pin (should start with "v")

{property}

string

The property of the widget you want to update: onLabel, offLabel, label, color, isDisabled, isHidden, and page

onLabel

string

the text on the button when the button is ON

offLabel

string

the text on the button when the button is OFF

label

string

the text used as widget label

color

string

button color hexadecimal, must include the hash # character urlencoded as %23

isDisabled

string

true or false

isHidden

string

true or false

pageID

string

pageID

Sync to the latest known state

You can update your hardware to the latest datastream value from Blynk.Cloud after your hardware went offline, and then came online again. Use Blynk.syncVirtual() to update a single virtual pin, or Blynk.syncAll() to update all virtual pins. See State Syncing for more details.

BLYNK_CONNECTED() { 
  // Called when hardware is connected to Blynk.Cloud  

  // get the latest value for V1
  Blynk.syncVirtual(V1); 

  // Request Blynk server to re-send latest values for all pins
  Blynk.syncAll()
}
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