Implementing a Blynk client (library)
We provide a reference C++/Arduino implementation of the library. It is very extensible and modular, just look at the list of supported hardware. Adding new connection types and Arduino-compatible boards is easy.
But some devices are programmed in other languages and environments, like:
  • Vendor-specific SDK and IDE
  • JavaScript, Node.JS, Espruino
  • Python, MicroPython
  • NodeMCU, eLua
This document hints how to write a custom library.

Blynk library main functions

  • Provide easy-to use API
  • Virtual pin handlers registration
  • Provide comfortable wrappers for some widgets
  • Manage connection
  • Should support different connection type/hardware, if applicable
  • Serialize/deserialize Blynk protocol
  • Should be portable across similar devices (or same technology/programming language), if possible
  • Should detect and notify the user about troubles where possible (especially Flood)
  • Handle direct pin operations [optional]

Adding new HW board to the Blynk mobile app

Different boards can be added by creating JSON board description file - look at the examples here. You can send us your own board description files for review and App integration.
There may be a problem that you want to start testing your implementation, but your board is not listed int the Blynk App. We have a "Generic Board" specially for such purposes. Or you can just select UNO board and check how it works using just virtual pins. Most digital pins should also work. Analog IO/PWM will not work in general, until we add your board to the App.

Blynk protocol

Blynk transfers binary messages with the following structure:
Command Message Id Length/Status Body 1 byte 2 bytes 2 bytes Variable
Message Id and Length are big endian. Body has a command-specific format.
Command and Status definitions: BlynkProtocolDefs.h
Another protocol description can be found here.
Typical Blynk library knows how to send(S) and process(P):
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S BLYNK_CMD_LOGIN + auth token
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SP BLYNK_CMD_PING
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SP BLYNK_CMD_RESPONSE
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SP BLYNK_CMD_BRIDGE
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SP BLYNK_CMD_HARDWARE
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S BLYNK_CMD_TWEET
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S BLYNK_CMD_EMAIL
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S BLYNK_CMD_PUSH_NOTIFICATION
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HARDWARE/BRIDGE command body

The body of these commands are encoded as a sequence of strings, separated by '\0' (Null character). Please note that the last value may be not Null-terminated.In the following command examples '\0' chars are replaced with spaces.

Pin mode

PinMode command is received by library after connection, or when a mobile application starts.
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pm <pin> <mode>
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pm <pin> <mode> <pin> <mode> <pin> <mode> ...
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Mode:
  • in - INPUT
  • out - OUTPUT
  • pu - INPUT_PULLUP
  • pd - INPUT_PULLDOWN

Digital pin operations

Digital write:
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dw <pin> <val>
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Digital read:
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dr <pin>
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Analog pin operations

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aw <pin> <val>
2
3
ar <pin>
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Virtual pin operations

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vw <pin> <param0> <param1> <param2> <param3> ...
2
3
vr <pin>
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Developer notes

  • Values in HW commands are plain text.
  • In response to dr/ar command, library should send dw/aw command on the same pin and with the same message id.
  • These situations should cause a connection drop or reconnection attempt: Message with ID=0 is received, Message with unknown type is received

Example implementations

Use these to play with the protocol and understand the basics:

Adding network interface

4 entities should be created to add a new network interface to Arduino library:
1 - Select connection interface that will be used for Blynk operation. This should be something like http://www.arduino.cc/en/Tutorial/WebClient
Based on the API of the connection, create the Transport. Some examples may be found in the Adapters folder:
  • BlynkTransportSerial
  • BlynkTransportCC3000
  • BlynkArduinoClient - should be reused, if possible
2 - Create Blynk representative class, which contains connection-specific helper functions (like begin).Examples:
  • BlynkEthernet
  • BlynkStream
  • BlynkCC3000
  • BlynkWildFire
  • BlynkYun
3 - Create BlynkSimple* header for your connection. This constructs main Blynk instance, so the user (mostly) doesn't need to get into such details.Examples:
  • BlynkSimpleEthernet.h
  • BlynkSimpleCC3000.h
  • BlynkSimpleWifi.h
  • BlynkSimpleUIPEthernet.h
4 - Create a simple example for your platform ;)
Last modified 4mo ago
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