Local Objects

Until now, we’ve looked into the capability of BAC0 to act as a “client” device. This is not a very good term in the context of BACnet but at least it is easy to understand. But BAC0 can also act as a BACnet device. It can be found in a network and will present its properties to every other BACnet devices.

What if you want to create a BACnet device with objects with BAC0 ?

You will need to provide local objects that will be added to the application part of the BAC0 instance. This part is called this_application.

What are BACnet objects

BACnet objects are very diverse. You probably know the main ones like AnalogValue or BinaryInput or AnalogOutput, etc. But there are more. Depending on your needs, there will be an object that fit what you try to define in your application. The complet definition of all BACnet objects fall outside the scope of this document. Please refer to the BACnet standard if you want to know more about them. For the sake of understanding, I’ll cover a few of them.

The definition of the BACnet obejcts is provided by bacpypes.object. You will need to import the different classes of objects you need when you will create the objects.

An object, like you probably know now, owes properties. Those properties can be read-only, writable, mandatory or optional. This is defined in the standard. Typically, the actual value of an object is given by a property name presentValue. Another property called relinquishDefault would hold the value the object should give as a presentValue when all other priorityArray are null. PriorityArray is also a property of an object. When you create an object, you must know which properties you must add to the object and how you will interact with thoses properties and how they will interact with one another.

This makes a lot to know when you first want to create one object.

A place to start

The enormous complexity of BACnet objects led me to think of a way to generate objects with a good basis. Just enough properties depending on the commandability of the object (do you need other devices to write to those objects ?). This decision hAVe an impact on the chosen properties of a BACnet object.

For any commandable object, it would be reasonable to provide a priorityArray and a relinquishDefault. Those propoerties make no sense for a non-commandable object.

For any analog object, an engineering unit should be provided.

Those basic properties, depending on the type of objects, the BAC0’s user should not hAVe to think about them. They should just be part of the object.

Working in the factory

BAC0 will allow the creation of BACnet objects with a special class named ObjectFactory. This class will take as argument the objectType, instance, name, description, properties, etc and create the object. This object will then be added to a class variable (a dict) that will be used later to populate the application will all the created objects.

The factory will take as an argument is_commandable (boolean) and will modify the base type of object to make it commandable if required. This part is pretty complex as a subclass with a Commandable mixin must be created fot each objectType. ObjectFactory uses a special decorator that will recreate a new subclass with eveything that is needed to make the point commandable.

Another decorator will also allow the addition of custom properties (that would not be provided by default) if it’s required.

Another decorator will allow the addition of “features” to the objects. Thos will need to be defined but we can think about event generation, alarms, MinOfOff behAViour, etc.

The user will not hAVe to think about the implementation of the decorators as everything is handled by the ObjectFactory. But that said, nothing prevent you to create your own implementation of a factory using those decorators.

An example

A good way to understand how things work is by giving an example. This code is part of the tests folder and will give you a good idea of the way objects can be defined inside a BAC0’s instance

def build():
    bacnet = BAC0.lite(deviceId=3056235)

    new_obj = ObjectFactory(
        properties={"units": "degreesCelsius"},
        description="Analog Value 0",
        properties={"units": "degreesCelsius"},
        description="Analog Value 1",
        presentValue="Default value",
        description="String Value 0",
        presentValue="Default value",
        description="Writable String Value 1",

    return bacnet


So it’s possible to create objects but even using the object factory, things are quite complex and you need to cover a lot of edge cases. What if you want to create a lot of similar objects. What if you need to be sure each one of them will hAVe the basic properties you need.

To go one step further, BAC0 offers models that can be used to simplify (at least to try to simplify) the creation of local objects.

Models are an opiniated version of BACnet objects that can be used to create the objects you need in your device. There are still some features that are not implemented but a lot of features hAVe been covered by those models.

Models use the ObjectFactory but with a supplemental layer of abstraction to provide basic options to the objects.

For example, “analog” objects hAVe common properties. But the objectType will be different if you want an analogInput or an analogValue. By default, AnalogOutput will be commandable, but not the analogInput (not in BAC0 at least as it doesn’t support behAViour that allows to write to the presentValue when the out_of_service property is True). Instead of letting the user thinking about all those details, you can simply create an analogInput and BAC0 will take care of the details.

Actually, BAC0 implements those models :

analog_input, analog_output, analog_value, binary_input, binary_output, binary_value, multistate_input, multistate_output, multistate_value, date_value, datetime_value, temperature_input, temperature_value, humidity_input, humidity_value, character_string,

Again, the best way to understand how things work, is by looking at code sample :

# code here

State Text

One important feature for multiState values is the state text property. This define a text to shown in lieu of an integer. This adds a lot of clarity to those objects. A device can tell a valve is “Open/Close”, a fan is “Off/On”, a schedule is “Occupied/Unoccupied/Stanby/NotSet”. It brings a lot of value.

To define state text, you must use the special function with a list of states then you pass this variable to the properties dict :

states = make_state_text([“Normal”, “Alarm”, “Super Emergency”]) _new_object = multistate_value(

description=”An Alarm Value”, properties={“stateText”: states}, name=”BIG-ALARM”, is_commandable=True,


Engineering units

Valid Engineering untis to be used are :

ampereSeconds ampereSquareHours ampereSquareMeters amperes amperesPerMeter amperesPerSquareMeter bars becquerels btus btusPerHour btusPerPound btusPerPoundDryAir candelas candelasPerSquareMeter centimeters centimetersOfMercury centimetersOfWater cubicFeet cubicFeetPerDay cubicFeetPerHour cubicFeetPerMinute cubicFeetPerSecond cubicMeters cubicMetersPerDay cubicMetersPerHour cubicMetersPerMinute cubicMetersPerSecond currency1 currency10 currency2 currency3 currency4 currency5 currency6 currency7 currency8 currency9 cyclesPerHour cyclesPerMinute days decibels decibelsA decibelsMillivolt decibelsVolt degreeDaysCelsius degreeDaysFahrenheit degreesAngular degreesCelsius degreesCelsiusPerHour degreesCelsiusPerMinute degreesFahrenheit degreesFahrenheitPerHour degreesFahrenheitPerMinute degreesKelvin degreesKelvinPerHour degreesKelvinPerMinute degreesPhase deltaDegreesFahrenheit deltaDegreesKelvin farads feet feetPerMinute feetPerSecond footCandles grams gramsOfWaterPerKilogramDryAir gramsPerCubicCentimeter gramsPerCubicMeter gramsPerGram gramsPerKilogram gramsPerLiter gramsPerMilliliter gramsPerMinute gramsPerSecond gramsPerSquareMeter gray hectopascals henrys hertz horsepower hours hundredthsSeconds imperialGallons imperialGallonsPerMinute inches inchesOfMercury inchesOfWater jouleSeconds joules joulesPerCubicMeter joulesPerDegreeKelvin joulesPerHours joulesPerKilogramDegreeKelvin joulesPerKilogramDryAir kiloBtus kiloBtusPerHour kilobecquerels kilograms kilogramsPerCubicMeter kilogramsPerHour kilogramsPerKilogram kilogramsPerMinute kilogramsPerSecond kilohertz kilohms kilojoules kilojoulesPerDegreeKelvin kilojoulesPerKilogram kilojoulesPerKilogramDryAir kilometers kilometersPerHour kilopascals kilovoltAmpereHours kilovoltAmpereHoursReactive kilovoltAmperes kilovoltAmperesReactive kilovolts kilowattHours kilowattHoursPerSquareFoot kilowattHoursPerSquareMeter kilowattHoursReactive kilowatts liters litersPerHour litersPerMinute litersPerSecond lumens luxes megaBtus megabecquerels megahertz megajoules megajoulesPerDegreeKelvin megajoulesPerKilogramDryAir megajoulesPerSquareFoot megajoulesPerSquareMeter megAVoltAmpereHours megAVoltAmpereHoursReactive megAVoltAmperes megAVoltAmperesReactive megAVolts megawattHours megawattHoursReactive megawatts megohms meters metersPerHour metersPerMinute metersPerSecond metersPerSecondPerSecond microSiemens microgramsPerCubicMeter microgramsPerLiter microgray micrometers microsieverts microsievertsPerHour milesPerHour milliamperes millibars milligrams milligramsPerCubicMeter milligramsPerGram milligramsPerKilogram milligramsPerLiter milligray milliliters millilitersPerSecond millimeters millimetersOfMercury millimetersOfWater millimetersPerMinute millimetersPerSecond milliohms milliseconds millisiemens millisieverts millivolts milliwatts minutes minutesPerDegreeKelvin months nanogramsPerCubicMeter nephelometricTurbidityUnit newton newtonMeters newtonSeconds newtonsPerMeter noUnits ohmMeterPerSquareMeter ohmMeters ohms pH partsPerBillion partsPerMillion pascalSeconds pascals perHour perMille perMinute perSecond percent percentObscurationPerFoot percentObscurationPerMeter percentPerSecond percentRelativeHumidity poundsForcePerSquareInch poundsMass poundsMassPerHour poundsMassPerMinute poundsMassPerSecond powerFactor psiPerDegreeFahrenheit radians radiansPerSecond revolutionsPerMinute seconds siemens siemensPerMeter sieverts squareCentimeters squareFeet squareInches squareMeters squareMetersPerNewton teslas therms tonHours tons tonsPerHour tonsRefrigeration usGallons usGallonsPerHour usGallonsPerMinute voltAmpereHours voltAmpereHoursReactive voltAmperes voltAmperesReactive volts voltsPerDegreeKelvin voltsPerMeter voltsSquareHours wattHours wattHoursPerCubicMeter wattHoursReactive watts wattsPerMeterPerDegreeKelvin wattsPerSquareFoot wattsPerSquareMeter wattsPerSquareMeterDegreeKelvin webers weeks years