Embedded computer communication and control of DALI LED drivers G. K. Adam1, P. A. Kontaxis2,3, C. A. Bouroussis3, D. Ε. Ventzas1 and F. V. Topalis3 2
1 Department of Computer Science Engineering, Technological Educational Institute of Thessaly, Larissa, Greece,
[email protected] Department of Energy Technology Engineering, Technological Educational Institute of Athens, Athens, Greece,
[email protected] 3 Lighting Laboratory, National Technical University of Athens, Athens, Greece,
[email protected]
Abstract - Digitally controlled dimming of lighting is emerging as a key energy savings system. The Digital Addressable Lighting Interface (DALI) standard is emerging as the preferred controlling method due to its many advantages. This paper proposes the architecture of an embedded microcontroller for management and dimming control of digitally controlled lighting devices. The proposed system could deal with real-time dimming control of DALI led drivers. The functional performance and operation of the proposed control system architecture was evaluated based upon a BeagleBone Black microcontroller board. Keywords - BeagleBone Black, Control system, DALI LED drivers, embedded microcontroller.
I. INTRODUCTION
T
HE development of new approaches for efficient lighting could be summarized in improvements in lamps’ technology and electronic ballasts-drivers, software, and lighting control systems [1] - [6]. Regarding lighting technology, LEDs have proven to be a promising technology since they combine high efficiency, environmental benefits, high reliability and long lifetime [7]. Lighting consumes more than 20% of the total produced electrical energy and it represents 30 - 40% of the electricity consumption of commercial buildings [8] - [13]. Furthermore, lighting is one area where significant energy savings can be realized without sacrificing productivity [14] - [16]. Microcontrollers towards this direction offer the advantages of low cost and sharp application design and implementation. However, the demand for sophisticated features and intuitive controls in microcontrollers’ applications continuous to increase. Microcontrollers come with installed software modules that speed prototyping and development time and improve interoperability [17], [18]. Today there is a rapid implementation of such systems towards low-cost, high-resolution, digital electronic ballast control designs. Such systems typically integrate analog circuitry combined with digital modules under firmware control [19] - [21]. The purpose of this paper is to present first results of an ongoing research project on the implementation of a DALI driver control system, based on a BeagleBone black microcontroller board, for real-time processing. DALI (Digital Addressable Lighting Interface) is a communication protocol for lighting control. The control system interprets user data and sends appropriate DALI commands to the driver for commissioning and dimming purposes. The proposed architecture performs all the processing and communication operations with the driver and generates appropriate control signals for digital dimming operations.
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In section II is described the design methodology followed and the goals aimed to be achieved. In section III the implementation of the proposed system architecture is detailed. Sections IV and V presents the software modules developed and discusses the experimentations carried out and the evaluation of system’s functionality. Finally, section VI presents a brief discussion and conclusions on the proposed system. II. DESIGN OF AN EMBEDDED CONTROL SYSTEM FOR A DALI DRIVER CONTROLLER
The goal is to develop a low-cost embedded control system for the communication and control of DALI drivers for dimming purposes. In this direction the system development should be based upon a microcontroller board that supports such communication mechanism in real time. DALI protocol operates at 1200Hz that is a low frequency within the range of microcontrollers’ frequencies and communication mechanisms. The system architecture must be flexible and customizable, to such extend so that to be enhanced and modified according to various system specifications and requirements. The microcontroller must be capable to control most of driver’s operation aspects. Today, 16-bit and 32-bit microcontrollers have the ability to execute powerful instructions in a single clock cycle, and achieve high throughputs. A typical control scheme includes a microcontroller acting as a master controller for sending and receiving instructions to/from the driver unit (slave) and an isolation unit of optocouplers for isolating the control input. A. DALI interface The DALI protocol was first described in Annex E, IEC60929 standard for fluorescent lamp ballasts, and subsequently, it was updated to the new standard IEC62386, to include other lighting devices, such as LEDs. DALI requires only a pair of wires to form the bus for communication to all devices on a single DALI network. A DALI network consists of a controller and one or more lighting devices (up to 64 devices) that have DALI interfaces. DALI ballasts are capable of providing 256 levels of brightness that follow a logarithmic dimming curve. Data is transferred between controller and devices by means of an asynchronous, half-duplex, serial protocol over a two-wire differential bus, with a fixed data transfer rate of 1200 bit/s. The DALI data is transmitted using Manchester encoding. A DALI control interface voltage between 9.5 V and 22.5 V is considered a physical high signal (usually 16V), whereas a voltage in the ±6.5 V interval is taken as a physical low 125
signal. The current allowed to run through a network is limited to 250mA with a maximum consumption of 2mA per ballast [22] - [25]. DALI is based upon the master-slave principle; the master sends messages (frames) to any slave device in the system. A DALI message structure is made up of an address and a command. The address corresponds to one of the ballasts in the loop, and the command tells that particular ballast what to do. All modules execute commands with broadcast addresses. A frame sent by the master is called a forward frame; it consists of 19 bits (a start bit, address byte, command byte, two stop bits), while a backward frame sent by the slave is an 11 bits frame (a start bit, data byte, two stop bits). B. The proposed architecture The design and implementation flow of system development and implementation involves the initial assignment and synthesis of units, their specification analysis, the actual programming and configuration steps, and finally real-time experimentations of the application system for functionality verification. In our approach the DALI driver interface is connected to the digital inputs and outputs of the microcontroller through a board that provides digital isolation. In this way we have the DALI drives as a slave and the microcontroller as the master. The proposed control system under development contains most of the essential modules for ballast communication and dimming control. A host PC could be connected for debugging purposes or perform further configurations. A general view of the proposed system is given in Figure 1.
III. THE IMPLEMENTATION OF AN INTEGRATED PLATFORM An experimental testbed platform (Figure 2) was established using the BeagleBone Black ver. C1 microcontroller, a DALI led ballast driver, and in between, an opto-isolation board.
LAN/WAN Ethernet
Microcontroller
Ethernet controller
Memory module
Flash controller
PWM modules
Timers
Microprocessor
Flash memory
Ports
USB/Serial
Ports
Host PC
that provides network access, timers’ circuitry, digital PWM modules, and other specialized hardware units and ports for synchronous-asynchronous communication and programming. The microcontroller drives a DALI ballast device through an opto-isolation unit that acts as an interface between the ballast and the microcontroller. The microcontroller receives user commands as an input that converts into acceptable formats (that conform to IEC60929 DALI protocol standard), that routes over a two-wire voltage interface as appropriate signals to the ballast. An add-on board of optocouplers provides an isolation circuit for connecting to DALI ballast that drives an LED. For specific ballast management and dimming purposes a DALI software driver module was developed to control a DALI system. The above system was built and tested for performance upon specific microcontroller board.
Communication Control instructions
Control signals Opto-isolation unit DALI voltage bus DALI LED Driver
LED Fig. 1. Top-level block diagram of the controller reference design
The basic layout is based on a microcontroller that consists of a central processing unit, a memory module that facilitates data exchange between processor and other units, a flash memory controller, an Ethernet interface controller
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Fig. 2. Top-view of the embedded computer control test-bed system
A. Hardware system description The microcontroller used is a BeagleBone Black unit, a low-cost development platform, based on an ARMv7 Cortex-A8 processor architecture (TI Sitara AM3358AZCZ100), running at 1GHz, with 512MB DDR3 of RAM and 4GB 8-bit eMMC on-board flash storage. The AM3358 microprocessor is enhanced with image acquisition and graphics processing functions, peripherals and industrial interface options. The opto-isolation unit is a Dali click add-on board (by MikroElektronika) that communicates with target board microcontroller via four mikroBUS lines (RST, CS, PWM and INT) and transfers data between the microcontroller and DALI devices over a two-wire differential bus by means of asynchronous, half-duplex, serial protocol. It features two optocouplers that provide an isolated DALI communication circuit interface. The board is powered by the Beaglebone microcontroller with 3.3V power supply. 126
A DALI control interface voltage between 9.5V and 22.5V is considered a physical high signal, whereas a voltage in the ±6.5V interval is taken as a physical low signal. As the microcontroller digital outputs are CMOS (0– 3.3V) it is necessary to use an adapting level circuit to convert the 3.3V to the corresponding levels of the control signals. Several manufactures have developed such units of CMOS-DALI interfaces with low power supply (e.g. 3,3V). Dali click is such an adapting level circuit. The target ballast device used is a DALI led driver with input voltage 12/24V DC, output voltage 12/24V DC, output current (max) 5000mA, LED min load 1W and max power 120W. The electronic ballast provides the LED with a constant voltage (CV mode). The Dali click board is optically isolated from the DALI ballast and communicates with the ballast via a two-wire connection. The microcontroller communicates with Dali click via two lines. The signals used are the transmit signal (DALI_TX) to send commands to the DALI ballast and the receive signal (DALI_RX) to receive ballast information. The 3.3 volt logic is translated at a higher voltage logic (16V) on the DALI bus. This provides the appropriate voltage for dimming control. The microcontroller can generate different voltage levels to control the communication and transfer the data for dimming purposes. Figure 3 shows the connections between Dali click and BeagleBone microcontroller. VCC
R2 10kOhm
R3 100kOhm U2
RST 1B4B42 C1 100pF
DALI
2
4
D1 1
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R4 6kOhm
3 R1 10kOhm
INT U1
VCC
R5 10kOhm DALI_RX
BALLAST
DALI click
BeagleBone Black Microcontroller
Fig. 3. Communication of DALI click and microcontroller
When a forward frame command is executed optocoupler U2 enables the transmission from the microcontroller to the ballast. DALI ballasts react only when a query command is executed that requires a feedback. Optocoupler U1 deals with the reception of the backward frame when such a query message has been sent. A high level signal in DALI turns into low level in the microcontroller digital input DALI_RX. When DALI_TX is put in high (high level signal) diode in U2 is not biased and its phototransistor is open, giving a high level. When DALI_TX is put in low (low level signal) the LED is biased and the transistor is closed. The control software developed in the microcontroller is responsible for inverting the signals’ values (due to the optocouplers’ signals level inversion) and perform the Manchester encoding/decoding. B. Embedded computer operating system For the embedded computer operating system we have chosen and customized a version of the Linux operating
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system - an Angstrom distribution. The Angstrom system is a Linux distribution for embedded devices (PDAs, Microcontrollers boards, Mobile phones, etc.). The BeagleBone Black unit comes with Debian Linux (Linux beaglebone 3.8.13-bone70) pre-loaded on the board's flash. In order to establish a specific operating platform Angstrom Linux was selected. An Angstrom firmware image (Angstrom v2012.12-beaglebone-2013.06.20) was downloaded for BeagleBone Black, and then compiled and installed (into a microSD card). Further on, it was updated and configured to support kernel modules manipulation. For this purpose, kernel source files and make utilities were installed (opkg install kernel-headers and opkg install kernel-dev) in the user’s kernel source directory. Into that directory (/usr/src/kernel) a scripts file was compiled (make scripts) that enabled utilities used for kernel module building. Finally, a symbolic link of the modules build directory was created to this path of the kernel source directory (ln -s /usr/src/kernel /lib/modules/3.8.13/build). IV. SOFTWARE MODULES DEVELOPMENT A. The ballast communication and control modules Within this integrated development platform software modules were developed in C for communication and control of ballasts based on DALI protocol specifications. The DALI protocol communication was implemented as a kernel driver module loaded into the user’s kernel source directory. Any application can call driver’s functions to write and read from a DALI device. All the development and compilations were carried on the microcontroller’s board without any need for cross-compiling. According to the DALI communication protocol a forward frame command consists of 19 bits (1 start bit, 1 address byte, 1 data byte, 2 stop bits). The bits are sent most significant bit (MSB) first. The packet is sent as a bi-phase Manchester encoded packet. The two stop bits have no phase change. The Manchester code is a digital encoding format in which symbol ‘1’ is represented by a falling edge (high followed by low), and symbol ‘0’ is represented by a rising edge (low followed by high). The backward frame sent by the slave is an 11 bits frame with the same characteristics as the forward frame (1 start bit, 1 data byte, 2 stop bits). DALI operation frequency is 1200bps, which means that 1 bit time is 1s/1200 = 833,33μs. Both the high and low pulses have equal width, which is equal to half the bit period (Te = 416,67μs). B. Dali driver module development This is a kernel module that facilitates the communication of the BeagleBone Black microcontroller with a DALI driver based on the DALI protocol. Once this module is successfully compiled and loaded into the kernel memory, afterwards any application can make use of driver’s function calls to communicate and control a DALI driver based on DALI protocol specifications. Overall the functionality of the DALI driver module is shown in the following flowchart (Figure 4). Two important file operations of this driver module are DALI_write and DALI_read for sending and receiving accordingly commands to/from DALI ballast. In particular, DALI_write encodes each forward frame
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into Manchester coding (where two states are sent for one bit) and fills in a forward frame list that consists of two stop bits first, then a data byte, an address byte, and a start bit last. There is no phase change for the stop bits. Finally, sends the frame with most significant bit first through the defined as an output GPIO port to the DALI click DALI bus interface. For every forward frame bit, two states are transmitted. Timer is initiated and each bit state is transmitted every 416μs (half bit period). init Microcontroller Initialisation
B. Application development Embedded computer operating system An example of a simple C code application template (DALI_app) that demonstrates the basic communication operations (DALI read and DALI write commands) with a DALI ballast through this kernel driver module is provided below.
Initialise timer, GPIO ports DALI Initialisation Enable file operations User application calls
receive
Α.2. Insertion Then, the driver is loaded into the kernel’s memory (insmod DALI_drv.ko) and made accessible by changing its group (chgrp dialout /dev/DALI_drv) and adding read and write permissions for the owner and the group (chmod 660 /dev/DALI_drv). All modules loaded into the kernel are listed in system’s modules file (cat /proc/modules). At the devices directory (ls –l /dev/DALI_drv) we can reconfirm that the module was loaded successfully as a character device (cat /proc/devices). We can obtain further information about the module using the lsmod command.
send
DALI read
DALI write
Manchester encoding
Manchester decoding N
Driver close ? Y end Fig. 4. DALI driver module functionality flowchart
V. EXPERIMENTATIONS A. Dali driver module installation At first we place the module driver (DALI_drv.c) and Makefile into the user’s kernel source directory, e.g. within a subdirectory e.g. DALI (/usr/src/kernel/DALI/). Into this directory we compile the driver module (make). Α.1. Compilation The following Makefile is used for driver module compilation: KERN_SRC:= /lib/modules/$(shell uname -r)/build PWD := $(shell pwd) obj-m := DALI_drv.o all: make -C $(KERN_SRC) M=$(PWD) modules clean: make -C $(KERN_SRC) M=$(PWD) clean
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#include #include int main(void){ char char forward_command [10], backward_command [10]; int fd = open( "/dev/DALI_drv", O_RDWR ); while (1) { // decimal format of command input: Address and Data bytes as a string scanf( "%s", forward_command); // command input, e.g. 255000, (FF 00) an indirect OFF command write( fd, forward_command, 1 ); // calls DALI_write file operation that sends the command into the ballast read( fd, backward_command, 1); }// calls DALI_read file operation that receives any answer from ballast close(fd); return 0;}
The application’s format of forward_command is a decimal representation of the address and data bytes defined as a string. The DALI driver module sends the forward_command as a DALI forward frame. The driver code adds appropriate start and stop bits. The bits are sent MSB first. The packet is sent as a bi-phase Manchester encoded packet. At a terminal we can monitor the execution through the dmesg command (dmesg). A sample execution view is shown below, e.g. for a direct level command 254242 (1111111011110010) for an arc value of 242. Into that code (in binary 1111111011110010) the algorithm adds one start and two stop bits: 1111111101111001011. Then, every bit is represented and transmitted as two states as follows: writeBuff = 254242 writeBuff[0] (address)= 254 writeBuff[1] (data)= 242 Executing DALI_write. Timer started. Bit val OUT is 1 \ Bit val OUT is 0 / two states of the START bit (1) Bit val OUT is 1 \ ADDRESS BYTE Bit val OUT is 0 / two states of address MSB (1) Bit val OUT is 1 \ Bit val OUT is 0 / two states of address bit (1) Bit val OUT is 1 \
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Bit val OUT is 0 / two states of address bit (1) Bit val OUT is 1 \ Bit val OUT is 0 / two states of address bit (1) Bit val OUT is 1 \ Bit val OUT is 0 / two states of address bit (1) Bit val OUT is 1 \ Bit val OUT is 0 / two states of address bit (1) Bit val OUT is 1 \ Bit val OUT is 0 / two states of address bit (1) Bit val OUT is 0 \ Bit val OUT is 1 / two states of address LSB (0) Bit val OUT is 1 \ DATA BYTE Bit val OUT is 0 / two states of data MSB (1) Bit val OUT is 1 \ Bit val OUT is 0 / two states of data bit (1) Bit val OUT is 1 \ Bit val OUT is 0 / two states of data bit (1) Bit val OUT is 1 \ Bit val OUT is 0 / two states of data bit (1) Bit val OUT is 0 \ Bit val OUT is 1 / two states of data bit (0) Bit val OUT is 0 \ Bit val OUT is 1 / two states of data bit (0) Bit val OUT is 1 \ Bit val OUT is 0 / two states of data bit (1) Bit val OUT is 0 \ Bit val OUT is 1 / two states of data LSB (0) Bit val OUT is 1 \ Bit val OUT is 1 /two states of STOP bit (no phase change) Bit val OUT is 1 \ Bit val OUT is 1 /two states of STOP bit (no phase change)
VI. CONCLUSIONS This paper proposes a microcontroller-based method of designing an essential DALI driver controller. An initial design of an embedded computer control system was developed and tested upon real-time conditions. The overall control system has the ability to control the main functions of a DALI led driver and perform dimming operations over DALI ballasts loads. The validity of the proposed system was evaluated through actual experiments on dimming various drivers LEDs loads. The platform developed seems to be capable to support further control initiatives regarding DALI driver control. The intention is to proceed further this research and the embedded computer platform using a subsystem of transformed to intensity and luminosity values extracted from camera image scenes for further experiments with driver dimming control and commissioning purposes. VII. ACKNOWLEDGMENT This research has been co-financed by the European Union (European Social Fund – ESF) and Greek national funds through the Operational Program "Education and Lifelong Learning" of the National Strategic Reference Framework (NSRF) - Research Funding Program: THALES. Investing in knowledge society through the European Social Fund.
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IX. CURRICULUM VITAE George K. Adam was born in Chalkis, Greece, on April 29, 1965. He received the Diploma and M.Sc. degrees in Electronics and Automation Engineering from the Technical University of Sofia, Bulgaria, in 1989, and the Ph.D. degree in Computer Science from Strathclyde University, Glasgow, U.K., in 1993. Currently, he is an associate professor in the Department of Computers Engineering at the Higher Technological Educational Institute of Thessaly, Larissa, Greece. He is the author of more than 40 papers in scientific journals. Dr. Adam is an associate editor of the International Journal of Computers and Applications, and a member of the ACM and IEEE Societies. His research interests include computer systems design and applications, computerbased control, and mechatronics. Panagiotis A. Kontaxis received the Dipl. Degree in Energy Engineering from the TEI of Athens, Energy Technology Department, in 1996, the Dipl. Degree in Electrical and Computer Engineering from NTUA in 2003 and the M.Sc. Dipl. Degree in Energy Production and Management from NTUA in 2004. He is currently Lecturer at the TEI of Athens, Energy Technology Engineering department. His research interests include, daylighting, image sensors, energy saving, artificial neural networks and power quality. Constantinos A. Bouroussis was born in Karditsa, Greece in 1979. He received the Diploma in Electrical and Computer Engineering from the National Technical University of Athens in 2004. His is senior researcher in Lighting Laboratory of National Technical University of Athens and he has years of experience in lighting education. He is the author of 3 books and more than 20 papers in scientific journals and conferences. His research interests include lighting technology, lighting measurements, energy efficient lighting, daylight harvesting, computer vision and imaging sensors. Dimitrios Ε. Ventzas (Electrical & Mechanical Eng, 1979, SMISA) is professor at Computer Eng Dpt at TEI of Thessaly - Larissa with a PhD in Control and Instrumentation Eng and specialization at DSP, Image and Video Processing, Sensors & Measurements and Biomedical Eng. He was Research Assistant at University of Bradford, UK in multiphase flow, System / Electronic Eng at HARSA SA, Greek Railways and AMBER SA. He has taught at TEI Athens, Lamia and Larisa and at University of Thessaly Mech Eng and postgraduate courses of Mech Eng and Agricultural Eng at University of Thessaly. He is the author of various lecture notes and 20 / 80 papers at international Journals / Conferences with over 100 citations and 5 Books. He is a member of international Editorial, Organizing, Professional Committees. Frangiskos V. Topalis, PhD, is Professor at the School of Electrical and Computer Engineering of National Technical University of Athens. He teaches the course of lighting and photometry. He is director of the Lighting Laboratory. His area of specialization is photometry and lighting systems. He is author of two books and more than 150 papers on lighting. He has coordinated more than 50 projects in the field of photometry and lighting.
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