IV. IMPLEMENTATION TEST-BEDThe proposed personal sensor network control dc grid powered LED lighting system is depicted in Fig. 6. As can be seenin Fig. 6, there is a dc power mains panel that houses 2-unitof power factor correction (PFC) converters, each with powerrating of 750 W, running at greater than 95% power factor tooutput a 24 supply along the dc grid to the connected LEDThis article has been accepted for inclusion in a future issue of this journal. Content is final as presented, with the exception of pagination.TAN et al.: SMART PERSONAL SENSOR NETWORK CONTROL FOR ENERGY SAVING 5lighting system. The digital communication between the addressable LED lighting system and the personal sensor networkdistributed into the office space is a hybrid interface of standardized wired communication, DALI, and wireless communicators. Through this hybrid communication means, the ambientinformation is gathered by the sensors in a wireless manner andthen transmitted to the main PC, as illustrated in Fig. 6, to enable individual addressable ballast to switch on-off or dim therespective LED luminiaire.The personal sensor nodes platform employed in thisresearch composes of an ultra-low-power MSP430F2274 microcontroller and a CC2500 2.4 GHz wireless radio transceiverarranged in a star topology form within the specified 70office space. Taking advantage of the small constrained size ofthe office space, which is well within the capability of wirelesssensors without compromising on signal communication loss,a single-hop star topology WSN with all the wireless sensornodes within direct communication range to the gateway, isimplemented. The implementation cost of the proposed system,excluding the expensive LED luminaries, is quite comparableto the conventional fluorescent lighting system using similarwirings and protection subsystems. The extra cost for havingmore sensor nodes is also trivial as compared to the overallsystem cost, probably 1%.The address information of each LED lighting and the sensornodes are encoded to ensure that each sensor node controls itsrespective LED lighting. Taking into account the LED lighting,the preference value of each user for each sensor is changedflexibly versus the specific location of that sensor node. TheLED lighting system is controlled by the proposed smart wireless sensor network as illustrated by the following steps:• Decision Making Algorithm: To determine the time tochange the mode: LDR sensor and PIR sensor.• Detection Phase: To detect and calculate the lumen value.• Receive the output signal from sensor node, classify thissignal and then send it to DALI controller to control theLED lighting.The access point (AP) of the distributed personal sensor network, like the base station of a star wireless sensor network, istasked to calculate and determine the time to control the sensingfrequency of sensor node as well as to operate the mode of PIRsensors whenever possible. For example, LDR sensors controlthe LED lighting system during office hours from 8:30 A.M. to5:45 P.M.; after office hours the mode which human movement isdetected by PIR sensors is activated. An overview of the lightingcontrol schedule set in accordance to occupants’ activities in afull day is shown in Fig. 7. After the time is specified, a messagefrom AP is sent to end devices (EDs) in the personal sensor network control system to select the operation modes. Based on thisinformation, an internal timer in each ED is activated to countthe operation time to change such modes properly.To adequate control the dc grid powered LED lighting systemto react according to the lighting need of individual office user,a closed loop PI control scheme has been employed to real-timeadjust the brightness of the LED luminiaires. In the proposedcontrol loop, the respective sensor of the wireless node, activated based on the designed decision making algorithm, sensesthe value of either lighting condition or occupancy for feedbackFig. 7. A full day lighting control schedule set in accordance to occupants’activities.periodically in every two seconds to the PI controller. By comparing with the preset user-defined reference value, the desiredcontrol signal, in terms of a specified dimming percentage oron/off level, is outputted from the AP node via the DALI network to control the LED luminiaire. Note that the address ofeach LED light is encoded into its assigned controlling sensornode. At times, a predetermined group of LED lights is controlled by one sensor node. By controlling the intensity of LEDlighting to reach the satisfactory level and in combination withthe use of the day lighting, it is seen that the energy is used efficiently with the best effort for energy saving.
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