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The programmable logic controller (PLC) is a very versatile computer processor. With it's various input and output modules, is capable of handling any electrical control system. When applying the PLC to a residential application, it can control the lighting, fireplace, motorized drapery and windows, etc. One draw back is the dimming requirements that a homeowner requires on lights in certain rooms, like the Dining room. The PLC does not presently have an output module for this dimming function. There is a product out in the market place that does a very good job of dimming lights on a room by room basis; the Grafik Eye.

The Grafik Eye is a product of Lutron Electronics Co. That lets you control every light in a room with a touch of a button. It is a self-contained computer processor that allows the setting and recalling of up to sixteen lighting scenes. The Grafik Eye product line has elegant button keypads that are very attractive on the homeowner walls. But what is very useful is the Grafik Eye RS232 interface offered by Lutron to interact with other control systems. It is this RS232 interface, when connected to the PLC, which gives the Grafik Eye the smarts to be incorporated as a whole house control system.

The Grafik Eye lighting control system links up to eight control units (six zones each) and sixteen button keypads. Each control unit and button keypad have their own unique addresses that communicate on a four-wire (daisy-chain) connection. The RS232 interface unit connects to this four-wire bus and then to the PLC via a three-wire cable. With the interface connection, the PLC monitors all the buttons that have been pushed or released on button keypads strategically connected throughout the home. Also, the PLC can send messages to the Grafik Eyes to select any scene and also receive the status of all control units on the communication four-wire bus.

Writing a ladder logic program in the PLC is the smarts we talked about earlier that transforms the Grafik Eye product to a whole house control system. Connecting a standard momentary switch to the PLC, when closed, can send a message to the Grafik Eye to turn on a scene. Likewise, a button pushed on a Grafik Eye keypad can now operate a motorized drapery to open via ladder logic written in the PLC. The control options become endless with the incorporation of a PLC into a Grafik Eye lighting control system. To the homeowner, this marriage of a PLC to a Grafik Eye system gives a very powerful and flexible electrical control system.

Lovol Control Systems, (based in Vancouver, Canada) has successfully implemented this type of lighting control system in many small and large residential projects. Lovol has created a PLC package that can be installed by any qualified electrician. Check web site at 'www.lovol.com'.