Wireless Transceiver for Dot Matrix (WiTrix)

Wireless Transceiver for Dot Matrix (WiTrix) AZIZUDDIN A. AZIZ, HANITA DAUD, SHARIFAH ZAHIRA SYED IEDIN Department of Electrical & Electronics Engineering Universiti Teknologi PETRONAS Bandar Seri Iskandar, 31750 Tronoh, Perak Darul Ridzuan MALAYSIA Abstract: - This paper proposes a system that enables a transmitter block to transmit messages wirelessly to the dot matrix at the receiver block. Dot matrix displays are widely used in various applications for various purposes. Among them are advertising board, public service information, traffic notifications, greeting note and many more. The hardware of the system comprised of two blocks controlled by a PIC microcontroller. The 4x4 keypad gives input to the transmitter microcontroller and the Vacuum Fluorescent Display (VFD) acts as the transmitter display. The Dot Matrix is placed as the receiver display. RF hybrid transceiver pair that acts as the heart of the wireless transmission is interfaced to the microcontrollers using the encoder/decoder pair. The RF transceiver pair transmits and receives the data based on purely RF transmission. The operability of the microcontrollers and the control of the workflow of the system was developed using C programming language. This project is a potential platform for enthusiasts of electronics project to integrate the use of microcontrollers, C programming and wireless transmission and for further expansion on outdoor message display. Key-Words: - Microcontroller, RF transmission, C Programming, Dot Matrix Display, Vacuum Fluorescent Display (VFD) 1 Introduction Dot matrix displays have been used in many applications in our daily lives. They are used to convey messages at most public places like banks, bus terminals, highways and also government agencies. It is one of the effective ways to convey messages to a large target group. The messages displayed must be timely and accurate. Nowadays, most of the dot matrix displays, if not connected in hard-wired mode to the controller station, they are being controlled remotely by certain software installed on a computer at the control station. They are not equipped to enable messages to be transmitted directly to the displaying unit without having to use a workstation or a computer or in other words wirelessly. The main focus of this work is to introduce an integrated system that transfers the messages wirelessly to the dot matrix display at the receiver. It uses Radio Frequency (RF) for the wireless transmission. The hardware consists of two microcontroller boards. One is connected to the keypad, Vacuum Fluorescent Display (VFD) and the transmitter module, while the other is connected to the receiver module and the dot matrix display. The microcontrollers control the operations of transmitting and receiving messages with the developed C language program embedded inside them. 1.1 Wireless Communications Wireless communication is one of the most vibrant areas in the communication field nowadays. Wired networks and communication are for communications between fixed locations, whereas wireless networks are mostly for communications between devices, with the device mobility being the primary benefit [1]. According to [2], wireless communication is referred to as unguided media that transports electromagnetic waves without utilizing a physical conductor in the electromagnetic spectrum ranges from 3 khz to 900THz. Integrating wireless communication with digital electronics has become an exciting field to explore especially in the evolving microcontroller-based applications that can result in cheap mass-produced digital circuits [3]. ISSN: 1790-5109 180 ISBN: 978-960-6766-94-7

1.2 RF Wireless Transmissions RF(radio frequency) is a portion of electromagnetic spectrum in which electromagnetic waves can be generated by feeding alternating current to an antenna [4]. Almost all wireless transmission use RF including AM, FM radio, TV, satellites, portable phones, hand phones as well as wireless networks. RF signals can be focused in one direction (directional) or in all directions (Omni directional) [5]. Generally RF transmission points to wireless communications with frequencies below 300 GHz [2]. Using wireless system, it is desirable to filter out unwanted and interference signals to prevent incorrect data from being received and interpreted. Since RF spectrum is crammed with noise and interference signals, a data control system is used. To achieve this, an encoder IC (HT12E) is connected as an interface between microcontroller and the transmitter and a decoder IC (HT12D) between the other microcontroller and the receiver module. For this project, RF modules to be used are the FM Hybrid Transmitter and Module by RFSolutions. The transmitter operates on 3-12V supply voltage and comes in SIL and DIL package. The receiver is built using PLL XTAL design and operates on 5V supply voltage. 1.3 Microcontrollers A microcontroller (also MCU or µc) is a computeron-a-chip, containing a processor, memory, and input/output functions. It is a microprocessor emphasizing high integration, in contrast to a general-purpose microprocessor (the kind used in a PC). In addition to the usual arithmetic and logic elements of a general purpose microprocessor, the microcontroller integrates additional elements such as read-write memory for data storage, read-only memory for program storage, EEPROM for permanent data storage, peripheral devices, and input/output interfaces. At clock speeds of as little as a few MHz or even lower, microcontrollers often operate at very low speed compared to modern day microprocessors, but this is adequate for typical applications. They consume relatively little power (milliwatts), and will generally have the ability to sleep while waiting for an interesting peripheral event such as a button press to wake them up again to do something. Power consumption while sleeping may be just in nanowatts, making them ideal for low power and long lasting battery applications. Microcontrollers are frequently used in automatically controlled products and devices, such as automobile engine control systems, remote controls, office machines, appliances, power tools, and toys. By reducing the size, cost, and power consumption compared to a design using a separate microprocessor, memory, and input/output devices, microcontrollers make it economical to electronically control many more processes [6]. For the project, two microcontrollers of different models were used, namely PIC18F458 for the transmitter and PIC16F877 for the receiver board. Both microcontrollers are manufactured by Microchip. 1.4 Dot Matrix Display A dot matrix display is a display device used to display information on machines, clocks, railway departure indicators and many other devices requiring a simple display device of limited resolution. The display consists of a matrix of lights or mechanical indicators arranged in a rectangular configuration (other shapes are also possible, although not common) such that by switching on or off selected lights, text or graphics can be displayed. A dot matrix controller converts instructions from a processor into signals which turns on or off lights in the matrix so that the required display is produced [7]. 2 Design and Approach The physical systems for this project are integrated as in Fig.1 below. VFD Transmitter block Antenna RF Transmission Keypad Dot Matrix display block block Fig. 1: Physical System of the project The messages are entered at the transmitter block using the keypad connected to Vacuum Fluorescent Display (VFD) which later will transmit the messages wirelessly to the receiver block where the dot matrix display is connected to. Here, the messages will be display to the users. The development and design of the circuits for transmitter and receiver boards, the RF interfacing connections with the encoder/decoder pair to the microcontrollers, and the peripheral hardware to the ISSN: 1790-5109 181 ISBN: 978-960-6766-94-7

microcontrollers is done using OrCad software. The circuitry designed needs to take a few matters into considerations: 1. To ensure that there is enough ports for the peripherals, especially at the transmitter part. 2. To ensure that the connections for particular peripherals such as the Vacuum Fluorescent Display and the Dot Matrix Display are aligned with the pin assignments in their driver C codes. 3. The electrical ratings of each component. 4. The power needed to power up both of the circuits. Serial data wired transmission checking, which involves the data transmission from the serial data-out pin of the encoder into the serial data-in pin of the decoder. Wireless transmission checking by connecting the serial data-out pin of the encoder to the data-input pin of the transmitter. The data is then being transmitted wirelessly to the receiver, in which its data-output pin is connected to the serial data-in pin of the decoder. 3 Results & Discussions Keypad VFD PIC 18F 458 Encoder Transmitter Transmitter Block 3.1 Project Flow and Architecture The specific architecture of WiTrix is explained by the block diagram shown in Fig. 3 and the operational flow chart shown in Figure 4 below. By referring to both of the figures, the operation can be described by the following steps. When the transmitter is powered up, the user is prompted with a welcome note, informing which button should be pressed next, either Button A, B or C, with: Dot Matrix Decoder PIC 16F 877 block Fig.2: System outline of the and Transmitter Blocks The development of each circuit as in Fig. 2 is conducted independently and being checked one at a time to ensure that every circuit constructed on the Vero board is working properly. After each block is working, then only the circuit integration or interconnection takes place. The system integration then witnessed the three stages of testing modes: Wired 4-bit parallel checking is done by connecting both the microcontrollers input and output pins directly without the intervention of the encoder/decoder pair and the RF transceiver. Button A jumps back to the welcome note prompt, and prompts the user to enter either A or B or C again. Button B displays the button functions of the keypad. Button C will direct the user to press any number from 0 to 9 to view the messages. As soon as the messages are displayed on the VFD, the same message will also appear on the Dot Matrix display. This is due to the parallelism employed during sending the characters to the VFD, the microcontroller at the transmitter also sends a specific 4-bit data to the receiver for the microcontroller at the receiver to identify and display the message that suits the 4-bit data from the transmitter. The messages can be entered as many as 20 times, and after that, the transmitter program needs to be restarted again by pressing either A, or B, or C. The 20-times iterations, however, can be stopped at any time before the end of the 20 th iteration by pressing Button D, and that the user will be prompted to press Button E to restart again the program by choosing A, or B, or C as explained above. ISSN: 1790-5109 182 ISBN: 978-960-6766-94-7

Transmit ter side VFD Keypad Transmitter Fig. 3: The Overview of WiTrix Operation side Dot Matrix Display the transmitter block since the transmitter block is handling more hardware peripherals. Ports A, B, C and D of PIC18F458 are almost completely occupied by the three peripherals (the keypad, the VFD and the encoder). Therefore, a bigger space of memory to allocate the long C programming is needed to control the peripherals and to have a faster operation compared to if the transmitter block were to use PIC16F877. Table 1: PIC18F458 port utilization Port Description A0-A3 4-bit output to encoder B0-B7 8-bit keypad C1-C3 Control bits for VFD D0-D7 Data bits for VFD Total ports used: 23 out of 33 I/O pins Start Welcome Instruction Press Input from keypad Press Press Prompt user to press # to view Input from keypad Press 0-9 View message on VFD. The same message is displayed on DOT MATRIX Escape? Press D & E N Input from keypad=20 x Yes Fig. 5: The transmitter board connection to the transmitter circuit and its peripherals Restart back Fig. 4 The flowchart of WiTrix operation PIC16F877 is used to control the receiver board, where it is programmed to be able to identify the input received from the decoder, and match it to the input of one of the 10 messages. 3.2 Microcontroller Two PIC microcontrollers of different models are used for this project, namely PIC18F458 for the transmitter block and PIC16F877 for the receiver block. PIC18F458 is chosen to control the operation of Table 2: PIC16F877 port utilization Port Description A0-A3 4-bit input from decoder B0-B2 Control bits for Dot Matrix display B4-B7 Data bits for Dot Matrix display Total ports used: 11 out of 33 I/O pins ISSN: 1790-5109 183 ISBN: 978-960-6766-94-7

Fig. 7: The schematics of the connection of the transceiver to the encoder and decoder Fig. 6: The receiver board connection to the decoder and the Dot Matrix display 3.3 Communication Medium For this prototype, the RF Hybrid Transceiver pair from RFSolutions is used as the wireless communication medium. The transmitter and the receiver are respectively connected to the HT12E encoder and HT12D decoder from Holtek Semiconductor as the interface with the microcontrollers, as shown in Fig. 7. The encoder and decoder pair is used to interface the microcontroller with the RF transceiver. At the transmitter microcontroller, ports A0 to A3 are connected to the encoder pins of AD 8 to AD 11. The encoder will receive 4 bits of data from the transmitter microcontroller according to which keypad button is pressed. The microcontroller response to respective input from the keypad and is summarized in the Table 3 below: The outputs from port A0 to A3 will then be channeled to the encoder to convert it into serial data. The serial data produced will be channeled to the RF transmitter, and will be transmitted to the receiver side. Table 3: Transmitter microcontroller operating algorithm Keypad Microcontroller output bits Vacuum Fluorescent # Input A A A A Display message pressed to PIC 3 2 1 0 1 0x11 0 0 0 1 1. Available 2 0x12 0 0 1 0 2. Taken an MC 3 0x14 0 0 1 1 3. Out 4 a while 4 0x21 0 1 0 0 4. Not in office 5 0x22 0 1 0 1 5. Out to meeting 6 0x24 0 1 1 0 6. Lunch break 7 0x41 0 1 1 1 7. Out- Site Visit 8 0x42 1 0 0 0 8. 1-week leave 9 0x44 1 0 0 1 9. Leave your msg 0 0x82 1 0 1 0 10. Don t disturb Table 4: microcontroller operating algorithm Microcontroller input bits ot Matrix Displ A3 A2 A1 A0 message 0 0 0 1 Available 0 0 1 0 Taken an MC 0 0 1 1 Out 4 a while 0 1 0 0 Not in office 0 1 0 1 Out to meeting 0 1 1 0 Lunch break 0 1 1 1 Out- Site Visit 1 0 0 0 1-week leave 1 0 0 1 Leave your msg 1 0 1 0 Don t disturb At the receiver, the received signal is converted into serial data, and is channeled to the Data In pin of the decoder. The decoder will then decode the serial information into 4-bit data. The produced 4-bit data are then directed to the receiver microcontroller ISSN: 1790-5109 184 ISBN: 978-960-6766-94-7

input pins of A0 to A3. The response of the receiver microcontroller is tabulated as in Table 4 above. The use of the system can be extended to a further distance. A larger receiver display can be used for better applications. An enhanced keypad or a keyboard may be used to enter the characters so that individual letters, numbers and characters can be typed and send to the display at the receiver. Future work will be concentrated on doing this improvement. References: [1] Tse, David and Viswanath, Pramod. (2005), Fundamental of Wireless Communication (1 st Edition) New York, Cambridge University Press. Fig. 8: The final prototype of WiTrix Fig. 8 above shows our final working prototype that has been tested at Universiti Teknologi PETRONAS. 4 Conclusions & Recommendations The project has successfully met its objective to transmit and receive data in wireless mode to the dot matrix display. The main components of the prototype; the microcontrollers, the encoder and decoder pair and the RF transceivers have proven to be working smoothly although initially it was rather doubtful since the three components are manufactured by different parties. The interesting part of the wireless transmission is although the signal transmission cannot be guaranteed to be 100 percent reliable; the signal transmission in this prototype is fast and precise. The receiver displays the exact messages as in the transmitter display. Also, the time interval taken to display the message is tested and it is less than 3 seconds. The measured maximum distance between the transmitter and the dot matrix display is 25m. The range can be further extended by supplying a higher value of current. Apart from knowing that the microcontroller is doing a good job based on the written C programs, the efficiency of the RF transceiver pair is also clearly projected by the fast and accurate transmission. Also, the use of the encoder-decoder pair has helped in converting the parallel data into serial data, and vice versa. [2] Forouzan, Behrouz M. (2004). Data Communications and Networking (3 rd Edition) New York, Mc Graw-Hill. [3] Bates, M. (2000), Introduction to Microelectronic Systems: The PIC 16F84 Microcontroller (1 st Edition) Great Britain, Arnold Publishers. [4] Aitkin Hugh G. J. The Continuous Wave: Technology and the American Radio, 1900-1932 (Princeton University Press, 1985). [5] Alan Butters. Radio Frequency Identification: An Introduction for Library Professionals. Australasian Public Libraries v19.n4(2006) pp.2164 174. [6] http://en.wikipedia.org/wiki/microcontroller [7] http://en.wikipedia.org/wiki/dot_matrix_display ISSN: 1790-5109 185 ISBN: 978-960-6766-94-7