Radio-controlled systems eliminate the need for communication wiring between wall-mounted switches and the Programmable Logic Controller (PLC). Radio transmitters communicate with the PLC via radio frequency (RF) signals. PLCs control other residential electrical devices that are not part of the radio-controlled system. Linking the PLC and the radio-controlled system together provides for an overall control system that can employ multiple transmitters for multiple location control.
The communication link between the PLC and the radio-controlled system is an RS232 interface unit. The connection is via a standard DB-9 serial cable between the PLC and the RS232 interface unit. Both devices should be mounted close together as per the RS232 minimum power requirements.
The PLC is connected to residential electrical devices that are not part of the radio-controlled system (outdoor lights, motor operated drapes, fireplaces, etc). Because the two systems are linked via the RS232 interface, a button push on a radio-controlled keypad can now operate motor operated drapes or turn a fireplace on/off. Also, the PLC can turn on/off lights on the radio-controlled system based on its timeclock or security functions.
Radio frequencies from many other sources can interfere with proper operation of this type of control system however. These radio systems are also relatively expensive, but they are useful where the controlled electrical devices are difficult to access. They are also suited to retrofit applications where control wiring would be difficult or expensive to install.