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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)/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>

Other operations

info

TODO

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

Adding network interface

4 entities should be created to add a new network interface to Blynk:

  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 - can be reused, if possible
  2. Create Blynk representative class, which contains connection-specific helper functions (like begin). Examples:
    • BlynkEthernet
    • BlynkSerial
    • 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 ;)

Example implementations

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