Reducing the cost of running lighting systems is an increasingly important factor for commercial facilities. The price of energy is making building automation more common, using a wireless network and control nodes to switch off equipment when it is not needed to save cost.
For lighting systems, this is coupled with the increasing use of ‘daylight harvesting’ to minimize the use of artificial lighting and combine natural light with the appropriate illumination, whether it is halogen, fluorescent, or LED. This often means a re-design of the lighting environment, often including natural light from windows to enhance the office environment, and more direct control of the lighting system. This can be done with local sensors, but increasingly the lighting units are being connected with a wireless network to provide centralized control. This allows new control algorithms to be implemented for more efficient use of the lighting throughout the whole building, connecting other systems such as security and maintenance for more efficient facilities management. With access to the Internet, either directly through an office wireless network or accessed via a gateway, these systems can be controlled remotely for even more flexibility.
In the commercial environment, there are several factors influencing the implementation of a wireless network for the lighting system. Mesh networks such as the 802.15.4 ZigBee and Synapse Wireless’ SNAP provide a low power, low-cost self-contained approach optimized for building automation.
However, with 802.11 Wi-Fi being prevalent in the commercial environment, this becomes an option for controlling the lighting systems, allowing a direct link with enterprise systems and remote control via the Internet. High volume production of the 2.4 GHz 802.11 b and g chipsets for laptops and mobile phones means these devices are cost effective, and integration into a module simplifies the design more effectively than the 5 GHz 802.11a versions.
This then brings in issues of security and access control, and this capability is integrated into some of the devices. Autonomous Wi-Fi modules have fallen in price in recent years as volumes have risen, making them a cost effective way of adding wireless connectivity to lighting systems in the commercial environment without having to design a complex board and antenna system. Low power is not an immediate critical consideration, as there is a power source available for the lighting system, but temperature does have to be considered. If the network node is co-located in the lighting housing, there will be temperature issues that may have an impact on the performance of the network devices, so a low power option may be preferable.
The MRF24WB0MA and MB from Microchip are low-power, 2.4 GHz, IEEE Std. 802.11-compliant, surface-mount modules with all associated RF components – crystal oscillator, bypass and bias passives with integrated MAC, baseband, RF and power amplifier, and built-in hardware support for AES, and TKIP (WEP, WPA, and WPA2 security). The modules interface to Microchip PIC18, PIC24, dsPIC33, or PIC32 microcontrollers through a four-wire serial slave SPI interface that provides the interrupt, hibernate, reset, power and ground signals.
Figure 1: The MRF24WB0 Wi-Fi modules from Microchip.
The integrated module design frees the designer from RF and antenna design tasks and regulatory compliance testing, providing quicker time to market. The MRF24WB0MA module is approved for use with the integrated PCB meander antenna while the MRF24WB0MB comes with an ultra-miniature coaxial connector, approved for use with a list of pre-certified antennas.
The modules are designed for use with Microchip’s TCP/IP software stack, which has an integrated driver to implement the API that is used in the modules for command and control and for management of data packet traffic.
The combination of the module and a PIC running the TCP/IP stack supports the implementation of a wireless web server using 802.11 networking. The modules have regulatory approval for modular devices in the United States (FCC), Canada (IC), and Europe (ETSI). The modular approval removes the need for expensive RF and antenna design, and allows the end user to place the modules inside a finished product without requiring regulatory testing for an intentional radiator (RF transmitter). They also have Radio Type Approval Certification for Japan.
The SG901-1059-5H from Sagrad is a high-speed module supporting all data rates and the 802.11b/g/n Wi-Fi standards with a USB 2.0 interface to make it even easier to integrate. The high level of interoperability and low cost are desirable for high volume applications, and the module is supported by Windows and Linux OS. It uses a highly integrated MAC/BBP and RF single chip with a 150 Mbit/s PHY.
Figure 2: The Sagrad WiFly module.
Similarly, the IEEE 802.11a/b/g/n OEM modules from connectBlue have also been developed for integration into industrial devices in commercial environments. The modules provide state of the art low power features, compatibility, robustness, and reliability, minimizing the work needed to implement IEEE 802.11 in a device as they provide. Together with the driver package, the module includes all the necessary software, hardware, type approval, and EMC certification for easy adoption into numerous applications. The high-performance modules are developed for reliable, high demanding industrial devices and applications.
Figure 3: The connectBlue Wi-Fi module.
The RN-131G WiFly GSX from Roving Networks is another complete 802.11b/g module optimized for simple integration into equipment, making it suitable for controlling commercial lighting systems as well as other automation applications. With a small form factor and extremely low power consumption, it can easily be integrated into a system and incorporates a 2.4 GHz radio, processor, TCP/IP stack, real-time clock, crypto accelerator, power management, and analogue sensor interfaces. This complete solution is preloaded with software to simplify integration, minimizes development of the application, and, in the simplest configuration, the hardware only requires four connections (PWR, TX, RX, GND) to create a wireless data connection.
Additionally, the sensor interface provides temperature, audio, motion, and other analog data without requiring additional hardware, allowing it to be used with other daylight harvesting schemes such as motion detection. The WiFly GSX module is programmed and controlled with a simple ASCII command language and once set up, it can scan to find an access point, associate, authenticate and connect over any Wi-Fi network. This dramatically simplifies the installation of the lighting control systems, easily fitting into the local enterprise networks.
However, Wi-Fi is not the only way to get Internet access, as companies such as Synapse Wireless also provide a gateway for their networks to be remotely accessed.
Synapse’s EK2400 evaluation kit for Internet control of an embedded application lets the designer monitor and control a wireless lighting system locally or over the Internet, demonstrating how to change any or all of four, high-intensity, color LEDs. It can also be used to monitor the temperature and ambient light via sensors built onto each of the EK2400’s two demonstration boards. The EK2400 includes a personalized log-in to SNAPLighting.com for the Internet connection through the E10 gateway to allow users to interact with the application from any web browser.
The SNAP E10 is a rugged, powerful, embedded connectivity appliance built to interface directly with SNAP mesh networks. The E10 can collect data from SNAP devices for centralized storage, database processing or application monitoring, and bridges across TCP/IP without requiring firewall configuration or policy exceptions. It provides seamless connectivity of SNAP, Ethernet, Wi-Fi and even cellular traffic to centralized applications, databases or storage via a 400 MHz 32-bit RISC processor running an open, embedded version of Linux. It does not require any programming, but does provide access to SNAP nodes from custom applications developed in most standard programming languages, including Python, C, C#, C++, Java and even Visual Basic. These applications, as well as the SNAP devices themselves, transmit and accept standard remote procedure calls (XML-RPC) as well as updating ‘over the air’. Full Linux services are also available to administrators and natively hosted applications.
Synapse also provides a module for the remote, wireless control of lighting in commercial buildings as part of its Lighting Cloud Service, an Internet-enabled, wireless remote control and monitoring service for secure indoor or outdoor lighting applications. This is designed to control fluorescent, LED and HID electronic ballasts with dimming and true on/off functionality, while supporting a wide range of input voltages from all over the world. It supports either 12 V Pulse Width Modulation (PWM) or 0-10 V input while providing strong, reliable wireless signal strength based on the industry standard IEEE 802.15.4 radio frequency.
ZigBee is a key technology for building automation, providing a mesh network where each node passes data to the next. Unlike Wi-Fi, which needs a network of access points and so needs to be planned, this allows a ZigBee network to expand by connecting new nodes to the nearest neighbor. However, in a commercial environment, the ZigBee network will have to co-exist with many Wi-Fi networks, all running in the 2.4 GHz band, and this means careful design of the wireless node is necessary.
The Ember EM250 is a single-chip solution that integrates a 2.4 GHz, IEEE 802.15.4-compliant transceiver with a 16-bit XAP2b microprocessor, Flash, and RAM memory, and peripherals of use to designers of ZigBee-based applications.
The transceiver uses an efficient architecture that exceeds the dynamic range requirements imposed by the IEEE 802.15.4-2003 standard by over 15 dB. The integrated receive channel filtering allows for co-existence with other communication standards in the 2.4 GHz spectrum such as IEEE 802.11g and Bluetooth. The integrated regulator, VCO, loop filter, and power amplifier keep the external component count low. An optional high performance radio mode (boost mode) is software selectable to boost dynamic range by a further 3 dB.
The XAP2b microprocessor is a power-optimized core integrated in the EM250. It supports two different modes of operation—System Mode and Application Mode. The EmberZNet stack runs in System Mode with full access to all areas of the chip, while the application code runs in Application Mode with limited access to the EM250 resources. This allows for the scheduling of events by the application developer while preventing modification of restricted areas of memory and registers. This architecture results in increased stability and reliability of the network nodes, vital when the control of lighting is involved.
Figure 4: The Ember EM250 ZigBee transceiver.
The EM250 has 128 kB of embedded Flash memory and 5 kB of integrated RAM for data and program storage, and it uses an effective wear-leveling algorithm in order to optimize the lifetime of the embedded Flash. This avoids accessing the Flash memory too often and spreads the access out between blocks so that certain individual memory locations are not used more often than others. To maintain the strict timing requirements imposed by ZigBee and the IEEE 802.15.4-2003 standard, the EM250 integrates a number of MAC functions into the hardware. The MAC hardware handles automatic ACK transmission and reception, automatic back-off delay, and clear channel assessment for transmission, as well as automatic filtering of received packets. In addition, the EM250 allows for true MAC level debugging by integrating the Packet Trace Interface.
To support user-defined applications, a number of peripherals such as GPIO, UART, SPI, I2C, ADC, and general-purpose timers are integrated. Also, an integrated voltage regulator, power-on-reset circuitry, sleep timer and low-power sleep modes are available. The deep sleep mode draws less than 1 μA, allowing products to achieve long battery life.
Figure 5: Ember’s EM250 development kit.
Atmel’s AT86RF230 is a low power 2.4 GHz radio transceiver especially designed for ZigBee 802.15.4 applications. The AT86RF230 is a true SPI-to-antenna solution with all the RF-critical components except the antenna, crystal and de-coupling capacitors integrated on-chip. Therefore, the AT86RF230 is particularly suitable for commercial lighting control applications alongside an external microcontroller.
The single-chip radio transceiver provides a complete radio transceiver interface between the antenna and the microcontroller with the analog radio transceiver and the digital demodulation, while including time and frequency synchronization and data buffering. The number of external components is minimized such that only an antenna, a crystal, and four decoupling capacitors are required. The bidirectional differential antenna pins are used for transmission and reception, so that no external antenna switch is needed.
Figure 6: Atmel’s AT86RF230 single chip ZigBee transceiver.
All these are options for the new generation of commercial lighting systems. With a focus on control and energy-reduction, a wireless network can provide a cost effective route to managing the lighting environment on its own and in combination with daylight harvesting techniques. In commercial applications, designers have the option of ZigBee networks with a mesh network of nodes that is easily extendible, or the integration of Wi-Fi modules to link directly to enterprise networks.
Standalone modules can be easily integrated alongside lighting systems, although co-existence and security issues have to be considered, depending on the choice of wireless technology. This gives system designers considerable flexibility to provide the optimum system solution for the specific environment and help organization and facilities managers reduce their energy bills.