by Chris Sontag

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Start • Intelligent Architechture • Putting the Pieces Together • Programming Brains • Building and Interface • Education Possible • Sources & PDF

BUILDING AN INTERFACE

Little code was needed to interface to the controller, since EMIT provides prebuilt emObject interface components and handles the communication details.

To simplify the task further, I used Symantex’s Visual Café and integrated the emObject components with the existing component toolkit. This way, I could select the objects from the component palette, add them directly to the applet, and easily manipulate layout and component properties.

The heart of the applet is an invisible object called emitjri (EMIT Java Runtime Interface). A new emitjri object is configured to communicate with this controller, which has a manufacturer ID of four and a device ID of 11.

All emObjects are passed a reference to the emitjri object. This way, emObject events can directly set variables on the embedded controller. Changes in embedded variables can also change emObject properties directly.

emitjri also contains function calls that enable the applet to directly set and get embedded variable values, as well as registering a callback to be notified when an embedded variable value changes.

An example of an emObject directly controlling an embedded variable is the watering on/off image switch. This object displays one of two images depending on its state (active or inactive).

You can establish the connection between the image switch waterOnOff and the embedded variable Water. So, whenever an ActionEvent occurs (when the switch is pressed and released on the interface), the event value (True or False) sets Water.

The embedded-controller clock is a good example of communicating variable state change to the display applet. The embedded variables Hrs, Min, and Sec change regularly, and these changes need to be relayed to the applet.

You may set up the callbacks for the embedded variables. Whenever the variable values change, notifyChange is called with the variable name and the new value. Similarly, we could have omitted the NotifyChange callback for Sec by setting a direct link between Sec and the emObject timeDisplay (see Listing 2).

Since emitjri handled the communications requirements, the majority of the coding effort was spent defining event-handler functions. Whenever a button is pressed, text entered, list items selected, checkboxes checked, and so on, events are generated. The event-handling functions for 24-/12-h clock, a.m./p.m., and day select are characteristic of many event handling functions that had to be created.

Many features were built into the user interface (see Photo 1) that could not easily be accomplished via hardware or by defining the interface completely within the embedded controller. The size of the applet increased to approximately 75 KB, but the controller and support interface hardware costs were reduced.

The end result is a Java class file that we can compress onto a 32-KB EEPROM and serve from the device. Or, emGateway could serve the client the prestaged class file along with the standard set of preinstalled emObjects.