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International Journal of Applied Electromagnetics and Mechanics 18 (2003) 127 –137 127 IOS Press

Design of a remote lighting control system using time division multiplex transmission
Sung-Jae Junga, Sung-Yong Yunb and Il-Hwan Kimc

of Control & Instrumentation Engineering, Kangwon National University,

Chunchon, Korea Tel.: +82 033 250 8789; Fax: +82-033-242-2059; E-mail: bDepartment of Control & Instrumentation Engineering, Kangwon National University, Chunchon, Korea Tel.: +82 033 250 8789; Fax: +82-033-242-2059; E-mail: cDepartment of Electrical & Computer Engineering, Kangwon National University, Chunchon, Korea Tel.: +82 033 250 6347; Fax: +82-033-242-2059; E-mail:

In this paper, a new distributive lighting control system for BA (Building Automation) i s presented. For optimallighting control and saving energy in buildings such as hotels, sch ools and offices, the group and pattern lighting control as well as individual lighting contr ol at one time are required. All the modulated lighting control terminals are connected to the central control unit through a pair of power lines. These power lines provide both po wer and signals to the each distributed terminal, and data are transmitted using the cyclic time division multiplex transmission algorithm. With this algorithm, a low-cost distributive control system for lighting applications has been achieved, allowing energy and maintenanc
e saving and increasing the reliability of the lighting control system.

1. Introduction 1.1. Background To provide a pleasant building environment, the ease of facility maintenance, manage ment and energy saving are required. Recently many new office buildings have been built as intelligent buildings.BA (Building Automation) systems, which are employed i n intelligent buildings, consist of a variety of subsystems such as air-conditioning, ele vators, fire alarms, security systems, and temperature monitoring and control systems. In general, to implement total building management systems, these subsystems are con nected to a central control system [1] .A new lighting control system is being develop ed rapidly, as the system becomes increasingly more sophisticated. It has the potential to produce significant benefits through energy savings due to reasonable

management of daylight and lighting, increased tenant comfort, planning flexibility for frequent alternation of office layout and simplified design and installation of lighting system. For optimum lighting control and efficient energy saving, it is necessary to i mplement group and pattern control of lighting, scheduling of lighting as well as indi vidual toggle-controls of lighting. Using the following strategies: daylight control, time control, task tuning of the light (i.e. adjusting necessary value to lighting levels valu e for each task) and so on, energy reduction up to 70 percent can be achieved [2].138 3-5416/03/$8.00 – IOS Press. All rights reserved. However, lighting control in modern bu ilding and offices is a typical example of where large amount and complicated connec tions of wirings are required. In the early days, connections between switches and lam ps (generally referred to as ?node?) are relayed with a complicated wiring system that basically joins every pair of related nodes (“point-to-point”), or employs star connecti on to manage the data flow in the network. In both cases: the cost of wiring is high and lacks the flexibility of modifying the configuration of the system in the future. The system is also difficult to debug and maintain and when the star connection is us ed, an entire group of nodes can cease to operate if the central compute is down. It is unrealistic to expect a lighting system in a large facility to be managed manually b y flipping switches or turning dials on the wall. The existence of these problems calls for a better solution. One that uses a single bus to connect a large group of intellige nce devices, allowing high interoperability between the nodes but practically has no in terference when some of the members are faulty. Intuitively, the Local Area Network (LAN), with its profound capability in moving large blocks of data among computers and their peripherals, appears to be an obvious option. However, although the perform ance of the LAN systems is high in terms of reliability and throughput, it is not cost effective and flexible for transferring short messages between a large number of intel ligent nodes intended to be economical, small in size, and easy to operate. An alterna tive solution that includes the advantages of the LAN and the economical aspects is t o introduce Intelligent Distributed Networks with specific protocols for linking large a mount of low costs and often single chip processors designed to interface with simple sensors or actuators (i.e. nodes). The processors are required to complete large numb ers of transactions per second with a good response time. As an example, in a central ized lighting control system, the connection of every nodes to a LAN through a comp uter equipped with a networking card and software, will be far too expensive and co mplicated for such a simple task. A more economical solution is to build into each n ode with a low cost processor (or micro controller) that is capable of sending signals, with a unified protocol, short messages to all other nodes in the network [3]. In this paper a new distributive control system for BA (Building Automation) lighting contro l used on general microprocessors, is presented. For optimal lighting controls and to save energy, the system has to control the group and pattern lighting controls as well as individual light controls at one time. In this paper, these functions are accomplish ed through a low-cost and simple microprocessor. A plurality of modulated light contr ol terminals are connected to the central control unit through a pair of power lines. T his power line provides both power and a signal to the each terminal and the data is transmitted through a cyclic time division multiplex transmission. With this structure

a low-cost distributive control system for lighting applications has been achieved, whic h includes the following advantages. – Increased reliability – data between nodes can be monitored, and history data, ca n be gathered to predict a failure in controlled nodes – Ease of Maintenance – it is easier for a supervisor and tenant to monitor, service and maintain through a distributive network system. – Energy savings – with a variety of strategies an optimal lighting system is adopted and the cost of lighting can be reduced. 1.2. Function required at the lighting control Recent intelligent building?s layouts are frequently altered with the use of movable par titions. For example, a room that has been used, as a warehouse might be a meeting room, and vice versa. In this case, the pattern of lighting has to be changed with the alternation. A lighting device such as streetlamps
Individual-control To control one node (lamp) at one place (switch), like a toggle-switch turns a lamp on and off in the conventional way To control one node (lamp) at several different places (switch), e.g., a stair-lamp Remote-control Group-control Pattern-control Scheduling To control several different lamps from one place (switch) at one time, such as a cor ridor-lamp, toiletlamp, and stair-lamp, which can be controlled by the building manag ement staff at the central control room. To form a specific lighting patterns. To accomplish a predefined lighting pattern acco rding to a schedule table that varies depending on the time of day, week and year, a lso between weekdays and weekend, summer and winter. Table 1

could be controlled at one time also exists. Particularly, the lighting devices largely d epend on the time of day, season and the place to be installed. This property is close ly related to flexibility that is also a crucial factor of system evaluations. To meet the se requirements of intelligent buildings, the system has to have not only functions to i mplement group and pattern lighting controls and individual light controls at one time, but also to the ability to schedule the lighting time according to the time of the day, the year, and regions. The above-mentioned functions are summarized in Tabl-e 1. 2. Implementation 2.1. System outline Figure 1 shows the basic block diagram of the proposed lighting system. This distribu tive lighting control system is made up of intelligent communication devices, called n odes, which are logically combined. A node may be a basic wiring device such as a switch, a Sensor, a Terminal Unit (T/U) and an Interface Unit that is connected to a PC via a RS-232C serial communication and is controlled by it.The design of the syst em using the proposed specs could be much more efficient and economical than conventional ones. Lighting nodes (slaves) and control units (Master) at one region can b e freely tapped onto a common communication line. The solid line of Fig. 1 is a tran smission medium, which uses a pair of twisted lines over 1.2 mm in diameter. The tr ansmission rate is about 9,600 bps. Due to the transmission lines effect in long (> 50 0 m) cables, signal attenuation on long distance may necessitate the frequent use of r epeaters, at distances of less than 500 m. It is possible to transmit signals long distan

ce by using repeaters [6]. This twisted pair plays the role of providing power (VCC s upplied to each devices) transmission for every switch and Terminal Unit (T/U) as we ll as a signal transmission,that is, from view of both power and signal transmission. T he communication method proposed in this paper is a kind of power line communicati on. Thus, there is no medium for providing power as depicted in Fig. 1. With this fe ature, the installation is simplified and cost is reduced. Figure 2 shows a practical sig nal transmitted at the communication line. As you see, the incessant fluctuations from +24 voltage to ?24 voltage of the communication line makes the power supply each device, e.g., switch, T/U, through bridge diodes in their power supply stage. Every lig hting node has a unique address, which can be easily varied at any time. We give a different designation to the number allocated lighting nodes. That is, just call ?address? the number to switch, ?channel number? to T/U. Thus, Switches have address from 0 to 255 and T/U have channel number from 0 to 63, which has 4 loads (lamps) per one. So it is possible to individually turn on and off a total of 256 lighting lamps. A lso, n this paper there are a total of 72 pattern switches that can control individual li ghting lamps up to 256 by just one handling. In the similar way, total 127 group swi tches. The number of each lighting node is summarized as follows.

– Individual switch: 1 ? 256, which controls just one T/U matched at one time – Group switch: 1 ? 127, which controls T/U matched up to 256 at one time – Pattern switch: 1 ? 72, which forms pattern T/U matched up to 256 at one time – T/U: 1 ? 256, which is connected to lamps, that is, directly turn on and off lamps – Master: 1 – Interface unit: 1, which is connected to the PC through a RS-232C The whole system has been designed to be controlled from one central control unit, called master. This master has authority to access the transmission medium; it plays an important role in cyclically transmitting data including address, mode and control data, with a transmission rate of 15 ms/unit. When the address or channel number that the nodes (switches, T/U) received from master through the communication medium is matched with what is allocated to them, the nodes will be activated and respond to transmitting data. If not matched, of course, they will shut down and not respond to. This also occurs when the switches are pushed or the state of T/U is changed. The nodes will transmit request signals to the master that is starting to send a cut-in signal explained in followed section. As mentioned above, all data, which is transmitted through communication medium, is monitored by an Interface unit.It is connected to the PC through a RS-232C that is a serial communication with several baud rates:1200 bps, 2400 bps, 4800 bps and 9600 bps, etc. Also a PC is connected with a LAN of the total BA(Building Automation) system, and employs a various and familiar lighting control strategies that are familiar to the users, such as tenant and building management staff. 2.2. Transmission of signal

2.4. The lighting nodes (slaves) Slaves consist of switches, T/U, interface unit, etc. Figure 7 shows a block diagram o f S/W, and T/U.These must include power supply stage to be provided with power ( VCC,+5 V) from the communication line. Like Master, slaves need proper controls to perform the specific function. In this system, functions required by slaves are achieved by a microprocessor, PIC16C73 [4], made by Microchips, which is not expensive in c ost and simple to use, which is what we have sought for. There is no difference exce pt several differences between S/W and T/U in function. Since S/W is manipulated by the hundreds in one day by users and its address is often changed by building manag ement staff, so that address of S/W is made be input by an infrared light. That of T/ U is made by input by the Dip S/W, since the address of T/U is rarely changed after T/U was installed once.

gure 8 shows a flow chart of slaves. If S/W is pushed or the state of T/U is chang ed, slaves will transmit cut-in signals into the communication line. Slaves always mon itor the communication line. If currently transmitting an address is matched with a pre defined that, a slave will get the control data and process it appropriately. 2.5. The ex perimental system Figure 9 shows the experimental system that consists of a master c ontroller, interface unit, terminal unit and a PC. Figure 10 shows the practical signals including the cut-in signal that is generated by the pushed switch. From this figure it can be seen that the cycle time of the proposed algorithm is about 16 msec. Also, th e response to the pushed switch is completed within 6 or 9 cycle times, which is dependent on the allocated address after the cut-in signal is sent to the master. Typica lly humans wait up to 1 sec for the lights to turn on. Therefore the response time de lay in this system is so small, a user will not feel uncomfortable. 3. Conclusions The development of a new distributive control system for intelligent buildings is descr ibed. In the presented system, data is transmitted using the cyclic time division multip lex transmission algorithm.

With this algorithm, distributive control system for lighting applications has been achie ved, allowing energy and maintenance saving and increasing the reliability of the light ing control system. A maximum of 513 slave nodes can be connected to a master tha t controls them and provides their required power.To implement the algorithm low-cost general microprocessors are used. LonWorks technology has been used to implement t he general distributed control system. It is a standard communication protocol that pro vides easy and fast implementation of the nodes in the network. However, it uses a s pecific Neuron Chip to accomplish the LonTalk protocol that is known to be very co mplex. It costs over 20 dollars, which is twice as much as a general microprocessor. A general intelligent building needs more than 500 nodes. So the cost to build a nod e is very important for applications such as a lighting control system. The algorithm presented in this paper will be appropriate to other applications where the amount of data transmitted is low, but simultaneous control of many nodes, such as group switch es, is needed. In the future, a hybrid network with wired and wireless communication will need to be studied, because recent lighting control systems also use infrared and radio frequency remote controllers. References
[1] R.A. Carlson and R. Giandomenico, Understanding Building Automation Systems, John Wileyc & Son s, 1994.

[2] W.R. Alling, The integration of microcomputers and controllable output balllasts – A new dimension in lighting control, IEEE Trans. On Industry Applications (September/October 1984), 1198–1205. [3] P.W.M. Tsang and R.W.C. Wang, Development of a distributive lighting control system using locals operation network, IEEE Trans. On Consumer Electronics 40(4) (November 1994), 879–889. [4] PIC16C7x-8-bit CMOS microcontrollers with A/D converter, Microchip Inc. Chandler, AZ, Microchip Technical Data D530390B.