A ridiculously simple tool for reading BACnet point values and sending them to a ridiculously simple messaging platform for the Internet of Things.
This application was written for the hackathon portion of the Smart Campus Summit - Beyond the Dashboard conference that was held at Cornell University on October 4th, 2017. The "hackers" were given a set of schematics for the building automation systems of Weill Hall and asked to determine the "key performance indicators" of the system with respect to the facility director, a controls technician, or a researcher. They had about two hours to design a dashboard and present it to the facility director.
The hackathon was a great success!
There is no installation, it's just a program. It depends on BACpypes for BACnet communication and dweepy to send "dweets" to the http://dweet.io service. If you don't already have these modules installed, get them from PyPI using pip:
$ pip install bacpypes dweepy
All of the configuration information is contained in a
JSON document that is one object containing two parts,
a config and a dweets, like this:
{
"config": {
},
"dweets": [
]
}The default configuration file name is bacpypes-dweet.json but that can be
changed through environmental variable SETTINGS or the --settings command line
option.
The config section is a JSON object that contains the configuration
parameters for your server/workstation to become a member of a BACnet network.
These parameters are identical to those in the BACpypes INI file, and if you
already have an INI file then the config section is optional.
Here is the configuration that is in the project repository, you will have to customize it with your own IP address in CIDR notation, along with a BACnet device identifier (the object instance number of the device object) that will be unique on your BACnet network:
"config": {
"objectName": "bacpypes-dweet-gateway",
"address": "10.0.1.211/24",
"objectIdentifier": 599,
"maxApduLengthAccepted": 1024,
"segmentationSupported": "segmentedBoth",
"vendorIdentifier": 999
},The dweets section is an array of dweet configuration information which is
the name of the thing, the rate that the values should be dweeted, and the list
of tags. For example, this is a thing:
{
"thingName": "bacpypes-dweet-oa-conditions",
"interval": 30,
"tagList": [
{
"tag": "temperature",
"address": "10.0.1.210",
"objectType": "analogValue",
"objectInstance": 1
}
]
}A Python thread is created for every 'thing'. There is no restriction on the number of things that can be created, but there is a practical limit to the amount of BACnet communications traffic and dweepy API calls based on your network, number of devices, upstream bandwidth, etc. There is also a limit to the number of times per minute that a thing can dweet.
A 'thing' is collection of name/value content pairs that is published to a message broker. At the current time, the service is public and free, so play nice and pick a unique thing name.
This is the interval in seconds that you want the thing to dweet. There are limits to how fast a thing can dweet.
The tagList is an array of tag objects with a name, a description of
a BACnet device, object, and property reference, and some simple value
transformation options. For the sample configuration file with the project,
the content of the dweet will look something like this:
{
"temperature": 61.84400177001953,
"humidity": 76.8499984741211,
"pressure": 32.98500061035156,
"enthalpy": 25.211944580078125,
"wind_direction": 140.54000854492188,
"wind_speed": 0.6690000295639038
}These are the raw floating point values coming back from this particular weather station which are much more precise than they are accurate!
The name of the tag. I have found it easier to work with the dweets when the tag names are restricted to letters and numbers.
The BACnet address of the device that contains the object. This is usually
an IP address, but may also be in the form of net:addr for MS/TP and ARCNET
devices that are on field networks.
This is the object type enumeration value for the object to read. These are
often analog input objects or analog value objects, but they could be any
object type that BACpypes supports. Note that the object type value matches
the naming convention used by BACpypes rather than the analog-value form that
appears in the standard.
This is the object instance number, as expected.
These are optional configuration name/value pairs for a tag.
If the property is specified, it can be any property appropriate for the
object. If it is not specified, presentValue is used.
If decnum is specified, integer and real values are rounded to the specified
number of decimal points. A positive number such as two (2) will round to the
nearest hundredth, a value of zero (0) is rounded to the nearest integer.
While the rounding can also be applied to the value when it appears on a dashboard or other display, it's often easier to put it in this configuration so it doesn't appear unnaturally precise.
It would be nice to replace the address of a device with its device instance
number and have the application use the Who-Is BACnet service.
Replace the objectType and objectInstance with objectName and have the
application use the Who-Has BACnet service. If the object name is unique
in the entire BACnet intranet then it's not even necessary to specify the
device address. If the BACnet object name was exactly the same as the tag
name, then even that could be optional.
Provide a way to use Read-Property-Multiple service, perhaps all of the values for a dweet can be read at once.
Provide a way to use Change-of-Value notifications so reading the value isn't necessary, the application will cache the last good value and send a dweet when any of the tag values change.