Virtual Pins

Send and receive data from device

Virtual Pins is a way to exchange any data between your hardware and Blynk app. Think about Virtual Pins as channels for sending any data. Make sure you differentiate Virtual Pins from physical GPIO pins on your hardware. Virtual Pins have no physical representation.

Virtual Pins are commonly used to interface with other libraries (Servo, LCD and others) and implement custom logic. The device can send data to the App using Blynk.virtualWrite(pin, value) and receive data from the App using BLYNK_WRITE(vPIN).

Virtual Pin data types

All Virtual Pin values are always sent as Strings and there are no practical limits on the data that can be sent. However, there are certain limitations on the hardware side when dealing with numbers. For example, the integer on Arduino is 16-bit, allowing range -32768 to 32767.

To interpret incoming data as Integers, Floats, Doubles and Strings use:

param.asInt();
param.asFloat();
param.asDouble();
param.asStr();

You can also get the RAW data from the param buffer:

param.getBuffer()
param.getLength()

Blynk.virtualWrite(vPin, value)

Use BlynkTimer when you use this command to send data. Otherwise your hardware may be disconnected from the server

Send data in various formats to Virtual Pins.

// Send string
Blynk.virtualWrite(pin, "abc");

// Send integer
Blynk.virtualWrite(pin, 123);

// Send float
Blynk.virtualWrite(pin, 12.34);

// Send multiple values as an array
Blynk.virtualWrite(pin, "hello", 123, 12.34);

// Send RAW data
Blynk.virtualWriteBinary(pin, buffer, length);

Calling virtualWrite attempts to send the value to the network immediately.

Note: For virtual pins with numbers > 127, the V128 syntax is not available. Please use plain virtual pin number, for example:

Blynk.virtualWrite(128, "abc");

BLYNK_WRITE(vPIN)

BLYNK_WRITE is a function called every time device gets an update of Virtual Pin value from the server (or app):

To read the received data use:

BLYNK_WRITE(V0)
{   
  int value = param.asInt(); // Get value as integer

  // The param can contain multiple values, in such case:
  int x = param[0].asInt();
  int y = param[1].asInt();
}

BLYNK_WRITE can't be used inside of any loop or function. It's a standalone function.

Note: For virtual pins with numbers > 127, please use BLYNK_WRITE_DEFAULT() API

BLYNK_WRITE_DEFAULT()

Redefines the handler for all pins that are not covered by custom BLYNK_WRITE functions.

BLYNK_WRITE_DEFAULT()
{
  int pin = request.pin;      // Which exactly pin is handled?
  int value = param.asInt();  // Use param as usual.
}

Blynk.beginGroup(), Blynk.endGroup()

When Blynk.virtualWrite() is called, server stores the provided value along with a timestamp. If you make several consecutive commands, timestamps will be different for every datapoint. If you'd need to assign a single timestamp for a batch of values, you can group them together:

Blynk.beginGroup();
Blynk.virtualWrite(V1, "abc");
...
Blynk.virtualWrite(V10, 123);
Blynk.endGroup();

This approach can improve charts rendering and CSV reports when many datapoints should have similar timestamp

Blynk.beginGroup() will determine the timestamp for the commands that follow. Alternatively, you can specify the timestamp explicitly (using ezTime library here):

uint64_t ts = (uint64_t)UTC.now() * 1000 + UTC.ms(LAST_READ);
Blynk.beginGroup(ts);
...
Blynk.endGroup();

Here, ts is a Unix Timestamp (UTC) with milliseconds, which you can get from Timezone / Location API.

Blynk.syncAll()

Requests all stored on the server latest values for all widgets. All analog/digital/virtual pin values and states will be set to the latest stored value. Every virtual pin will generate BLYNK_WRITE() event.

BLYNK_CONNECTED() {
    Blynk.syncAll();
}

Blynk.syncVirtual(vPin)

This command updates individual Virtual Pin to the latest stored value on the server. When it's used, a corresponding BLYNK_WRITE handler is called.

Blynk.syncVirtual(V0);

To update multiple pins, use:

Blynk.syncVirtual(V0, V1, V6, V9, V16);

Blynk.setProperty(vPin, "property", value)

This command allows changing widget properties