Read a BACnet value by subscription

🟢 Beginner

bacnet variable

osp-bacnet osp-web osp-variables

In this example you will learn how to communicate with a BACnet device and read data on it by subscription.

• Configure the BACnet module connection using module.bacnet and device.bacnet.

• Subscribe to change notifications using OBJECT_SUBSCRIPTION mode in owner.bacnet to receive updates pushed by the device.

• Use SINGLE_SUBSCRIPTION as an alternative to receive updates only when PRESENT_VALUE or selected properties change.

• Display the subscribed value on a dashboard using a value subscription widget.

git checkout origin/osp-bacnet-configuration .
git checkout origin/osp-web-configuration .
git checkout origin/osp-variables-configuration .
git checkout origin/example-bacnet-subscription .

Learning goals

• How to setup a connection to a BACnet device using module.bacnet and device.bacnet.

• How to read data using OBJECT_SUBSCRIPTION and owner.bacnet.

Bonus :

• Display the data in a frontend widget.

Steps

In this example we are using a BACnet stack using https://sourceforge.net/projects/bacnet/files/bacnet-stack/bacnet-stack-1.3.1/. This BACnet stack is running in a container using the following parameters.

bacnet_server:
    image: "nexus.sdnroot.net/bacnet_test_server:1.0"
    command: ["bacserv", "200001"]
    networks:
        - "back"
        - "outside_access"
        - "bridge"

Of course the whole example try to interact using nexus.sdnroot.net/bacnet_test_server:1.0 docker image. This is located in stack.external-services file. Please be careful to check if you can access this container or if your other tests devices are accessible from the OnSphere stack. For any connection problem refer to BACnet.

Note

Depending which BACnet type you are trying to read you may need an other OnSphere type see supported properties.

1. Setup the connection

First you need to configure the connection with a device. This is made in the bacnet.module file and device.bacnet file.

{
  "messagingConfiguration": {
    "clientId": "osp-bacnet-1",
    "host": "rabbit"
  },
  "networkConfiguration": {
    "subnetAddress": "172.17.0.0",
    "subnetMask": 16
  },
  "deviceIdentifier": 1234
}

{
    "deviceIdentifier": 200001,
    "moduleId": "modules.bacnet.bacnet-1"
}

2. Read the data on the BACnet device

Once the connection is correctly configured we can now configure the owner.bacnet file. Here we will determine what to read on the device. In this example we are configuring the BACnet module to subscribe one the value by using the OBJECT_SUBSCRIPTION parameter. This parameter asks the bacnet device to notify use about any changes on the BACnet object. Using SINGLE_SUBSCRIPTION option instead means that updates only arrive when a change on PRESENT_VALUE or any other selected BACnet properties happens (see supported properties).

{
    "readStrategy": {
        "strategy": "OBJECT_SUBSCRIPTION",
        "subscriptionRefreshFrequency": {
            "value": 30,
            "unit": "SECONDS"
        }
    },
    "linkedDevice": "root.bacnet",
    "object": {
        "type": "ANALOG_VALUE",
        "instance": 0,
        "property": "PRESENT_VALUE"
    }
}

3. Visualize the data

To visualize the data of your device, a dashboard, including a value subscription widget already linked to the status of your BACnet device and the test value, has been created.

{
    "configuration": [
        {
            "type": "ValueSubscription",
            "id": "mKQio7uo",
            "title": "",
            "valueSubscriptions": {
                "values": [
                    {
                        "id": "root.bacnet",
                        "type": "BOOLEAN",
                        "right": "READ_WRITE"
                    },
                    {
                        "id": "root.state",
                        "right": "READ",
                        "type": "DECIMAL"
                    }
                ]
            }
        },
        {
            "valueSubscriptions": {
                "values": [
                    {
                        "id": "root.callback",
                        "right": "READ_WRITE",
                        "type": "DECIMAL"
                    }
                ]
            },
            "basicWidgetSettings": {
                "showTooltip": true
            },
            "id": "ZfYR8aZ_",
            "type": "BasicInputOutputValue",
            "title": ""
        }
    ],
    "layout": {
        "lg": [
            {
                "w": 6,
                "h": 3,
                "x": 0,
                "y": 0,
                "i": "mKQio7uo"
            },
            {
                "w": 4,
                "h": 2,
                "x": 6,
                "y": 0,
                "i": "ZfYR8aZ_"
            }
        ]
    },
    "breakpoints": {
        "lg": 1200,
        "md": 996,
        "sm": 768,
        "xs": 480,
        "xxs": 0
    },
    "cols": {
        "lg": 12,
        "md": 10,
        "sm": 6,
        "xs": 4,
        "xxs": 2
    },
    "rowHeight": 150
}