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):
1
S   BLYNK_CMD_LOGIN + auth token
2
SP  BLYNK_CMD_PING
3
SP  BLYNK_CMD_RESPONSE
4
SP  BLYNK_CMD_BRIDGE
5
SP  BLYNK_CMD_HARDWARE
6
S   BLYNK_CMD_TWEET
7
S   BLYNK_CMD_EMAIL
8
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.
1
pm <pin> <mode>
2
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:
1
dw <pin> <val>
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Digital read:
1
dr <pin>
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Analog pin operations
1
aw <pin> <val>
2
​
3
ar <pin>
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Virtual pin operations
1
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:
​Python + MicroPython ​
​Node.js + Espruino​
​Arduino​
​Particle Core/Photon/Electron​
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 ;)

Node.js vs. C++ library

Export Project made with Blynk into a standalone app

Last modified 9mo ago

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