Joined but wireless

It is virtually impossible to imagine modern living without wireless communications. No matter whether we’re using the remote key to lock the car, changing the TV with the infrared remote or opening gates and doors at the company with an RFID transponder card. Even the nursery has long since gone “wireless”.

And so when the little one starts fussing the cordless phone, having received a request sent by the baby monitor via Bluetooth, uses its intercom function to call the parents at the other end of the apartment. Even though trends in the consumer goods markets are always a bit ahead of industrial applications, one important topic in industrial automation and building technologies has always been wireless communication with distant control units. That is no different in the elevator trade.

Some years ago the pros and cons of developing fi xed control panels vs. handheld terminals were certainly discussed, but the fact today is that everybody carries around a mobile control unit – the cell phone. These devices, in addition to telephone service, offer additional features such as taking and displaying photos and other multimedia content. This includes videos and launching programs . The present article introduces a solution developed for use with the bp308 control system, making it possible to access – wirelessly using Bluetooth – the display and keys on the control panel. Bluetooth is an industrial standard, developed at the start of the 1990s and codifi ed in IEEE 802.15.1, governing radio transmissions between devices over short distances. Its primary purpose is to eliminate hardwired connections between devices – in our case the connection between the control system and the control panel. Java™, being a platform-independent runtime environment, has long since become the quasi-standard for mobile devices. Independence from any given manufacturer is important since the hardware used in cell phone varies from the one to the next. Used here is the J2ME version (Java 2 Micro Edition), modifi ed for use with mobile terminal units. This version also offers, in addition to elements for user interface design and to store application data, an interface for communication via a Bluetooth module integrated into the mobile phone.

Important when designing the application is skillfully taking consideration of the diverse properties of the many and varied terminal units. Among the items to be taken into account are differing display resolution levels, supporting portrait and landscape displays, and peculiarities of the particular manufacturer’s implementation of the Java API or of the specifi c JSR 038, which is the Bluetooth programming interface. When designing GUIs for mobile terminal units with varying resolution levels, particular attention will have to be paid to straightforward input forms. The dialog elements should be realized following simple rules such as centered or fl ush left or right alignment, simple text wrapping or using scalable symbols and icons.

The actual transmission of the display data and, in the other direction, transmission of the input elements has been realized in the present case so that a clean depiction of the display and buttons is realized by way of the cell phone. There is no simulation of functionality with the exception of what is necessary to depict the display and the keys. This eliminates any dependencies between the application on the mobile phone and the control system software.

Protection against unauthorized access is realized with a dual MD5 hash handshake procedure authenticating both the application and the user. Since the module can also be used in a mobile constellation, having been connected at the USB host socket provided on the bp308 control system, need-oriented activation of the interface is possible simply by attaching or detaching the USB unit. Using the USB port offers the additional option of moving the Bluetooth module outside the switchgear cabinet. The range, without obstacles such as walls, goes from 1 m (Class 3) to 10 m (Class 2) and on up to 100 m (Class 1), depending on which hardware the manufacturer selects. Most mobile phones are fi tted with Class 2 units. The range of a Class 2 device is increased, however, when it interfaces with a Class 1 device – this in comparison to a pure Class 2 network. The improvement is achieved by the greater sensitivity and transmission power of Class 1 devices. In the solution presented here, a Class 1 unit is used at the bp308 control system.

This solution can be used wherever the controls, due to the installation circumstances, are not directly accessible and using a laptop or stationary PC appears to be impractical. Elevators without a separate machine room are an example of such a situation.

Roy Schneider, Graduate Engineer

Böhnke + Partner^® GmbH control systems