network are not required for the laboratory scale prototype but might be of service in a large-scale, real-world network. As Digi produces a drop-in, interchangeable ZigBee model to the 802.15.4 model, the prototype board could easily be upgraded to incorporate a ZigBee model if additional networking functionality is desired in a future application. The IEEE 802.15.4 protocol specifies a maximum data signal rate of 250 kilobytes per second and up to 65,000 nodes using local addressing. The necessary data shared within a zone in the wireless network are contained in short packets of less than 10 bytes. The small amount of necessary data transmission per additional node in the system implies that the zones could be scaled to be very large while maintaining fast zone-wide updating. However, the radios are limited in communication range and therefore data may require multiple hops to move between an edge node and the zone manager. With consideration of the need for multiple hops, the expectation of imperfect communication, which requires packets to often be sent multiple times, and the latency both within the wireless infrastructure and within the higher level unit software, a more realistic upper bound on the number of nodes per zone is on the order of 100. Implementing a zone on this scale also requires sufficient memory and processing power at the zone manager level to compute the optimal lamp settings for a problem of this size. The radio operates at 3.3 V in contrast to the 5 V supplied to the microcontroller. A second voltage regulator is employed to supply a constant 3.3 V to the radio and a voltage translator is used to moderate the communications between the radio and the microcontroller. The selection of the fluorescent ballast is important to the design of the lighting control interface. Unlike light-emitting diodes (LEDs) or incandescent bulbs, fluorescent lamps require very specific inputs to function properly and therefore require more sophisticated dimming hardware. With an LED, a direct current signal is simply turned on and off at a high rate with the proportion of on versus off time providing the level of dimming. An incandescent bulb can be dimmed by clipping the alternating current input for a selected width after the zero crossover points, twice per
network are not required for the laboratory scale prototype but might be of service in a large-scale, real-world network. As Digi produces a drop-in, interchangeable ZigBee model to the 802.15.4 model, the prototype board could easily be upgraded to incorporate a ZigBee model if additional networking functionality is desired in a future application. The IEEE 802.15.4 protocol specifies a maximum data signal rate of 250 kilobytes per second and up to 65,000 nodes using local addressing. The necessary data shared within a zone in the wireless network are contained in short packets of less than 10 bytes. The small amount of necessary data transmission per additional node in the system implies that the zones could be scaled to be very large while maintaining fast zone-wide updating. However, the radios are limited in communication range and therefore data may require multiple hops to move between an edge node and the zone manager. With consideration of the need for multiple hops, the expectation of imperfect communication, which requires packets to often be sent multiple times, and the latency both within the wireless infrastructure and within the higher level unit software, a more realistic upper bound on the number of nodes per zone is on the order of 100. Implementing a zone on this scale also requires sufficient memory and processing power at the zone manager level to compute the optimal lamp settings for a problem of this size. The radio operates at 3.3 V in contrast to the 5 V supplied to the microcontroller. A second voltage regulator is employed to supply a constant 3.3 V to the radio and a voltage translator is used to moderate the communications between the radio and the microcontroller. The selection of the fluorescent ballast is important to the design of the lighting control interface. Unlike light-emitting diodes (LEDs) or incandescent bulbs, fluorescent lamps require very specific inputs to function properly and therefore require more sophisticated dimming hardware. With an LED, a direct current signal is simply turned on and off at a high rate with the proportion of on versus off time providing the level of dimming. An incandescent bulb can be dimmed by clipping the alternating current input for a selected width after the zero crossover points, twice per
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