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):
S BLYNK_CMD_LOGIN + auth token
SP BLYNK_CMD_PING
SP BLYNK_CMD_RESPONSE
SP BLYNK_CMD_BRIDGE
SP BLYNK_CMD_HARDWARE
S BLYNK_CMD_TWEET
S BLYNK_CMD_EMAIL
S BLYNK_CMD_PUSH_NOTIFICATION
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.
pm <pin> <mode>
pm <pin> <mode> <pin> <mode> <pin> <mode> ...
Mode:
- in - INPUT
- out - OUTPUT
- pu - INPUT_PULLUP
- pd - INPUT_PULLDOWN
Digital pin operations
Digital write:
dw <pin> <val>
Digital read:
dr <pin>
Analog pin operations
aw <pin> <val>
ar <pin>
Virtual pin operations
vw <pin> <param0> <param1> <param2> <param3> ...
vr <pin>
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 ;)