RFID Door Unlocking System Evan VanMersbergen Project Description ETEC 471 Professor Todd Morton December 7, 2005-1-
Introduction In this age of rapid technological advancement, radio frequency (or RF) communication is emerging as one of the more promising and useful forms of data transfer. It is getting more and more difficult to find a person who has never talked on a cell phone, listened to the radio, or even logged onto wireless internet. One new technology that is on its way to becoming another common everyday use of RF communication, is Radio Frequency Identification (RFID). This is a relatively old technology, but new advancements within the last ten years have drawn quite an interest to those who need anything from a quick inventory count to instant price checks. Similar to bar codes, but much more powerful, RFID is a system of storing information on a tag and having the ability to read it from distances of up to forty feet. This year I propose to develop my own RFID system. I am planning to build an RFID Door-Access system. This project will use the ability of an RFID tag to signal a door to unlock. When one of these tags gets close enough to communicate with the antenna the reader will react and unlock a door if the tag contains the correct information. This system will also have the ability to accept new tags into the system, and remove them. The finished product will be composed of a reader, antenna, LCD screen, and a door lock indicator. Not everyone is familiar with this new technology, so I will briefly describe the two main parts of an RFID system. The reader is the heart of the system. It is the device that communicates with the tags through the antenna to unlock the door as well as communicate with the door lock and PC. There will be three transponder tags which hold data to send to the reader. These tags look like a credit card, but they contain an integrated circuit inside with 2k bits of memory and an antenna. -2-
Description The final product will be a stand alone system that receives a signal from a tag to unlock a door. Figure 1 shows an idea of what it will look like. Now not just any tag will be able to gain access. They will have to be programmed. Through a computer program the reader will receive the desired information and in turn send it to the tag to be stored. This data will be the name of the card holder. From that point on, any time that card is held near the antenna, the reader will display the card holder s name, and the time of entry on the LCD screen as well as unlock the door. The door will remain unlocked for five seconds, and then it will relock. To further ensure security, cards can be removed from clearance. All these programming of tags can be done through the computer after a security code is entered. RFID Tag Door Lock LCD Screen Antenna Reader Figure 1-3-
The reader will be controlled by the MC9S12DP256 microcontroller. Figure 2 displays which parts of the microcontroller will be used. This device was selected due to its sufficient memory capacity, my familiarity with its behavior, and its numerous other assets. The 256 K bytes of Flash EEPROM will contain all the software for operation. There are also 12 K bytes of available RAM that will be used for temporary variables. The microcontroller will run with a 16 MHz crystal. One of the major resources that will be utilized from this microcontroller will include the BDM input. This will be used through the software development process so I can save as much memory as possible for the actual code. There will also be an external reset circuit consisting of a pull-up resistor at the reset pin because the microcontroller already has internal reset circuitry. When it is set up, the microcontroller will receive tag programming information from the keypad. With keypad the user can program data onto cards, or delete cards from the system. A security code needs to be entered in order to do anything. This ensures security. There will be an LCD screen connected to the microcontroller through Port A (PA0- PA7) and Port K (PK0-PK2). This will display to the user the name on the card being read, whether or not access is granted, and the time of entry. Port B (PB0-PB2) will be used to unlock the door. The door lock is an electric dead bolt that is locked and unlocked base on an electric pulse. Each time a card checks in, it will unlock for five seconds before relocking. -4-
256 K Flash EEPROM 4 K EEPROM MC9S12DP256 Antenna Transponder 2 K RAM Key Pad Port B PTB 0-7 Port P PTP 0-2 S6700 16 MHz XTAL Port T PTT 0-2 Lock Reset Circuitry RESET BDM Port A PTA 0-7 Port K PTK 0-2 120 V AC BDM Connector LCD Wall Transformer Power Supply 5 V 1 A 24 V 1 A Figure 2 Typical RFID applications communicate on one of three frequency ranges. There is low frequency (125-134 khz), high frequency (13.56 MHz), and ultra high frequency (902-928 MHz). This system will operate on the high frequency spectrum. The RFID tags have been manufactured to communicate with the transceiver IC using the ISO 15693 protocol. The microcontroller is responsible for sending serial data to the transceiver. The transmit encoder then converts the data into the ISO 15693 RF protocol. In order for the reader to communicate with the transponding tags, it will amplitude modulate the desired 13.56 MHz RF signal using Texas Instruments S6700 Multi-Protocol Transceiver IC. The S6700, shown in Figure 3, is an integrated circuit -5-
designed precisely for RFID. It contains both an RF transmitter and receiver to communicate with the transponding tags, and it also contains a binary decoder for the transmitter and a binary encoder for the receiver. This enables the microcontroller to communicate with binary code. The S6700 will be connected to the microcontroller through Port P. It will require some external circuitry for operation. This requires a 13.56 MHz crystal, various capacitors, resistors, inductors, coaxial cable, and an antenna. Figure 3 After some searching and decision making, I have decided not to buy an antenna. An antenna for this application can be built without too much difficulty. Antenna prices were way too high (about $200 and up), but I will be prepared by winter to build an antenna with the help of a manual. An example of what it will look like can be seen in Figure 4. Figure 4 The last parts of this project are the transponding tags. These are cards manufactured by Texas Instruments and are compatible with the S6700 IC. The cards and the transceiver communicate using the ISO/IEC 15693 standard for wireless communication at 13.56 MHz. Figure 5 shows what they will look like. -6-
Figure 5 The power supply for this design requires a 5 volt source and a maximum current of 263 ma for the circuitry not including the electric bolt lock. A 24 volt source with a current of 110 ma is required for the electric bolt lock. The power supply will be accounted for by a wall transformer. It will take in 120 volts AC and output 5 and 24 volts and a maximum current of 1 amp. Software Requirements The software for RFID system will be programmed in C. I selected this language because it is just as capable as assembly language, but easier to read. The software will contain several different modules to make the device work. They are described in the following table. Module KERNEL Description The center of operation; a pre-emptive kernel that controls all the software modules through a time slicing routine. The user interface. It is a program that collects basic I/O data INTERFACE from the computer. A four digit security code must be entered in order to access this program. TAGREAD Master/Slave module that sends, receives and stores data from the SPI. -7-
UNLOCK A module to signal LEDs and unlock the door when a card is recognized. A prewritten module that sends messages to the LCD screen. It LCD_DISP will display information such as the card name, the time of check in, and when a card is deleted or added. TIME An internal real time clock that will display the time of a check in. A program that acts upon the information received through the INPUT_APP SCI. It initiates the application of other modules based on the input from the computer interface. The KERNEL, TAGREAD, UNLOCK AND LCD_DISP modules are the main modules. The modules that need input from the user are COMP_INT and TAGWRITE. They are primarily just for setting up the system. Once everything is set up, the system pretty much runs itself. Just a swipe of the card is all that is needed from the user. Of course these modules are needed later if changes are desired. User Interface The largest part of the user interface comes with the setup of the system. Cards will have to be saved, and the clock will have to be set. The computer interface will start with the LCD displaying as is seen in Figure 6. -8-
Figure 6 The user can press the A, B, C, or D buttons for one of four options: Add a card, delete a card, change the security code, or set the clock. Once the user selects an option the security code must be entered. It will look like Figure 7. The program will then prompt the user for information and complete the task. The user is automatically logged out at the completion of each of these tasks. A flow diagram is shown below in Figure 8. Figure 7 Once all cards are saved to the reader, the system is extremely easy to operate. All that is required is a sweep of the card and the reader will know what to do. This easy operation is one main advantage over key lock entry. -9-
Reset Incorrect Code Incorrect Entry A, B, C, or D A: Add New Card B: Delete Card C: Change Code D: Set Clock Enter code Correct Code Correct Code S C Set Hour Enter Set Minut Enter AM or PM Correct Code D Enter Correct Code N Enter New Name Enter Added Enter Name to Delete Enter Deleted Enter New Code Enter Code Changed Figure 8 The card will have to be waved within a few inches of the antenna in order for transmission to take place and gain access. One of three things will happen when a card is sensed by the system. The card can be recognized as a saved card and therefore unlock the door, the card can be read and not recognized as a saved card, or the card can have a read error. Each of these outcomes will be prepared for by a signaling LED on the door lock. A green LED will blink when the door is unlocked. A yellow LED will blink if the card is not identified on the system. A red LED will blink to indicate a read error. The -10-
lock will remain unlocked for a five second span when a good card is read. A flow diagram for the LCD and lock interface can be seen below. Reset Known Card Locked Read Error Unknown Card Flash Green LED Flash Yellow LED Flash Red LED LCD Display: Unlocked Name Time LCD Display: Read Error LCD Display: Unknown Card Unlock 1 Second 1 Second 5 Seconds Figure 9 Development Plan The sequence of development will begin over winter break. During this time I am responsible for reading and learning as much as I can about the microcontroller and the S6700. Understanding how these work and work together will be the key to how efficiently the system is constructed. By the beginning of winter quarter, I will have acquired all the major components: the microcontroller, the S6700 Transceiver IC, transponding tags, antenna parts, and various crystals, resistors, capacitors, and inductors. I want to start right away building the power supply. The next part to construct will be the antenna because the other hardware cannot be implemented until there is an antenna -11-
in the mix. It will be a loop antenna built out of conductive copper tape with resistive and reactive components soldered at the seam of the loop. A spectrum analyzer will be needed in testing the frequencies of the S6700 and the tags, as well as other noises. Antenna design will be followed by the transceiver setup. Setup includes building the crystal oscillator, attaching the antenna, mounting the IC, and constructing other external circuitry. They will initially be assembled on a solderless board, and will later be mounted on a PCB using point-to-point soldering. RF circuits can be tricky at high frequencies, so I allow two weeks for this task. A week will be given to build the power supply. The lock hardware will be the last of the hardware to build. I will acquire a full size door and transfer the LEDs and lock into it as is shown in figure 10. This will conclude the construction of the physical system right around week six of winter quarter. At this time the various software modules will be developed. This is a sketch of what the door knob will look like: Figure 10-12-
The UNLOCK, LCD_DISP, TIME, are able to be developed in about a week each. COMPUTER will be given two weeks to build. TAGREAD is the biggest challenge, so I allow the most time for its development. The final module, KERNEL, will be made at the end and will tie all the software together. The debugging process will be assisted by Motorola s BDM (Background Debugging Mode) circuitry. Assuming this all goes exactly according to the schedule shown below, there will be about three weeks to finalize all preparations. I will use this time to ensure that the system is as faultless as possible. I will also prepare materials for the presentation. There will be a full size door with the lock installed and the antenna attached in the center. I will have a poster that has pictures and diagrams explaining what RFID technology is and how it works. Visitors will be able to participate in programming their own cards, unlocking the door, and deleting their card so others can experiment. Winter 2006 Week 1 Week 2 Week 3 Week 4 Week 5 Week 6 Week 7 Week 8 Week 9 Week 10 Antenna Design Transceiver Hardware Setup Transceiver Hardware Setup Lock Hardware Design Assemble Hardware Assemble Hardware Develop UNLOCK module Develop LCD_DISP module Transceiver Protocol Code Transceiver Protocol Code -13-
Spring 2006 Week 1 Week 2 Week 3 Week 4 Week 5 Week 6 Week 7 Week 8 Week 9 Week 10 Transceiver Protocol Code Transceiver Protocol Code Hardware Review, Develop KERNEL Develop KERNEL Software Review, Final Software Assembly Final Prototype Assembly Preparation Testing Preparation Testing Code Review, Final Testing and Building Project Presentation Specifications Parameter Condition Units RFID Communications Protocol ISO 15693 Frequency Range 13.56* MHz Transponding Distance 2 Ft Supply Voltage 4.5 5.5 V I max 263 ma Max Power Dissipation 1.32 W Operating Temperature 0 o 50 o o C PCB Size 6 x 4 x 2 Inches Number of RFID Cards 3-14-
Number of Characters per Name 8 Serial Communication Protocol Asynchronous Master/Slave Security Code 4-9-8-3 Electric Bolt Lock Voltage 23 25 V Electric Bolt Lock Current 110 ma *13.56 MHz is found in a non-restricted band allocated by the FCC. Preliminary Parts Item Part Number Quantity Price Lead Time Distributor I q Microcontroller MC9S12C32 1 $10.65 1 week Digikey 35mA Transceiver IC RI-R6C-001A 1 $9.97 2 weeks Digikey 120mA Transponder RI-TH1-CB1A-00 3 $3.60 2 weeks Digikey N/A 2x16 LCD DMC-16207H 1 $10.80 1 week 3mA 13.56 MHz Crystal 300-8092-2-ND 1 $0.63 1 week Digikey N/A 16 MHz Crystal 300-604-ND 1 $0.65 1 week Digikey N/A Resistors Variable 15 $0.30 1 week Digikey 5mA Capacitors Variable 15 $0.50 1 week Digikey Inductors Variable 5 $0.33 1 week Digikey Coaxial Cable C5775-100_ND 1 $20.75 1 week Digikey N/A Copper Tape N/A 1 $9.32 2 weeks Stewart- N/A MacDonald LED LT814-81 3 $0.19 1 week Digikey 30mA RS232 MAX232A 1 $1.85 2 weeks Maxim 4mA Transceiver Electric Bolt HT-235 1 $265.99 3 weeks Fuzing 110mA Lock Totals $68.57 377mA -15-