Yun Serial-to-WAMP Bridge
This page describes how to install the necessary software on a Yun to enable remote control of the Yun's Arduino pins via WAMP. For an overview of all materials we have concerning the Yun, see
The big picture¶
The GPIO pins are managed by the Arduino MCU part of the Yun, while all network communcation is managed by the MIPS part. To get remote control, we need to pass data from the MUC to the MIPS/Linux part, and the send this over the network. We use WAMP for the remote communication. For the MCU-MIPS bridge we use the Firmata protocol.
There is an Arduino implementation of Firmata, which the MCU part runs. There are various implementations which we could run on the Linux side. In the end, using Node.js with
arduino-firmata and Autobahn|JS to provide WAMP connectivity proved easiest.
We offer Quick Setup instructions which use an image you can write to SD card, and which already has all the preparations for the serial-to-WAMP bridge installed for the Linux side. Otherwise you need to get AutobahnJS working on the Yun for the following.
The bridge code¶
Get the bridge code onto the Yun. If you've mounted the Yun's file system on your PC, just copy it over. Otherwise you can do
scp serial_to_wamp.js firstname.lastname@example.org:~/
from the directory the code is in (and where you replace the above IP with that of your Yun).
The MCU code¶
For the MCU, you need to install Firmata.
To run the bridge, just do
Configuring the connection to Crossbar.io¶
The code for the access to the GPIO pins can be kept generic, but you need to configure the connection to a Crossbar.io instance.
This is done via a config file in the same directory as the serial bridge code. This is a simple text file (
config), with one config option per line.
The provided example config file is
routerUrl: https://demo.crossbar.io realm: iot_cookbook deviceId: my_yun
which means that the serial-to-WAMP bridge will attempt to establish a WAMP connection to a Crossbar.io instance at
https://demo.crossbar.io and to the realm
iot_cookbook on that instance.
For all events and registrations it uses the deviceID. (This means that the deviceID needs to conform to the rules for WAMP URIs.)
The API exposes procedures in the format
The procedures are:
set_mode: set the mode for a pin, with the possible values
in(you actively read from the pin),
out(you write to the pin) and
watch(monitor the value of the pin)
digital_read: Read the state of a pin connected to digitial input device. Returns a Boolean.
digital_write: Write the state of a pin connected to a digital output device. Takes a Boolean.
analog_read: Read the state of a pin connected to an analog input device. Returns a numeric value, where the range depends on the input device .
analog_write: Write the state of a pin connected to an analog output device. Takes a numeric value, where the range depends on the output device.
reset: reset the state of the arduino part
For pins which have been set to
watch, value changes are published to the topics
and (presently unimplemented)
Note: It is possible to read from a pin which is watched - so you can combine automatic notifications for value changes with e.g. getting the current value on component startup without having to wait for the next value change.
Testing and usage examples¶
The code for this in the Crossbarexamples repository allows you to start a Crossbar.io instance to which the bridge can connect for development purposes.
This also serves an HTML page which attempts to read from an analog input and write to a digital output. This is mainly for illustrative purposes, to give you some examples for how the API can be used.
For examples of how remote GPIO can be used see e.g.