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RFID Security System Here’s a high-security system that’s very easy to build but offers you peace-of-mind for your home, car – in fact, anything where entry needs allow the good guys in but reject the bad guys. Team it with an electric lock and you can have a keyless entry system as well! I t’s a sad fact that in today’s world the need for property security is ever present. Our homes and business properties are a target for thieves and other criminals. We spend countless amounts of money on systems that have been designed to counter the would-be bad guys. The complexity of these systems ranges from a simple sticker that proclaims Batman will jump through the window and zap any burglar stupid enough to attempt robbing the premises, all the way up to computer controlled alarms systems that use satellites to protect our property and warn of a crime in progress. Although the system presented here does not quite communicate with satellites it will give a high level of protection and control access to any structure that it is monitoring. RFID? If you have an E-tag for the tollway, a micro-chipped pet or a late-model car with an immobiliser key, then you’re already using radio frequency identification (RFID) technology. Although RFID is not a 44  Silicon Chip new field and it has been written about in this magazine in the past, it is now available as a project for any person who wants to protect their property from unauthorised access. This system will give control over who has access to your home, car or any other building you care to mention. The system is installed in a position that will allow the users access to the protected building. A tiny (keyring-sized) RFID tag is held close to the sensor. The system detects the tag and compares its “signature” with those stored in memory (up to eight). If, and only if, a match is found, an on-board relay is enabled for one second. This relay could be used to disarm a burglar alarm or unlock a door. If the detected tag is not one of those stored in memory then the system can be used to trigger an alarm or to sound a warning that an unauthorised access has been attempted. The advantage of this is that tags can be changed and the system reprogrammed at will, so if a tag is stolen or even if someone attempts entry who is no longer allowed, that tag will have no effect except to flag an unauthorised entry attempt. The operating principals of RFID were explained in a previous article (July 2003) so if you want to know how the system works in detail you should read that article. Copies are available from SILICON CHIP. Basically, RFID operates by generating a magnetic field then looking for any modulation on that field. RFID “tags”, when bought within range of the scanning coil will send out a unique series of bits. The on-board microprocessor decodes these bits and outputs a data frame from pin 1 which is sent to RB0 (pin 6) of IC2. The range of this system Fig.1: a basic RFID setup consists of a reader is around 4cm which, al(or interrogator) and transponder. Low frequency systems though not a lot, is ideal for rely on inductive coupling to provide transponder power. siliconchip.com.au The project is very easy to build – all the hard parts (the RFID module and the detection coil) are prebuilt, which leaves you with only a handful of components to solder onto the PC board. The relay output can switch an electric door strike, a car central locking system, another alarm or just about anything you want! by Jeff Monegal the application presented here. Looking at the circuit diagram shows that there is not much to the system at all. The RFID part consists of a pre-built module that generates the necessary RF field used to scan the tags as they are bought within range of the scanning or detection coil. As well as “reading” the data from the tag, the coil also provides power to the tag via inductive coupling. It’s a minute amount of power but enough to “wake up” the tag and cause it to transmit its unique code back to the coil. The data frame consists of 42 bits which is detected and fed to the PIC16F628 microprocessor. The inter- The “works” of the RFID tag is tiny, as this photo shows. Very close to actual size, this is the same tag that’s encased on the keyring shown above left. siliconchip.com.au nal software strips off the unwanted bits of the frame to leave the last 24. If you think that this cuts down on the number of different combinations then consider this: 24 bits = 2 to the power of 24, equals 16,777,216. The circumference of Earth is 40075km... If you think of Earth as a giant chocolate wheel you would need a pin spacing of 2.4 meters around the full circumference of the wheel to equal this number of bit combinations. Another way of looking at it is, if each tag is randomly programmed when manufactured, you could line up 24 people and get each one to toss a coin, “1” for heads “0” for tails... the chance of one of the combinations being repeated again is one in 16,777,216... If the coins are tossed once every minute the probability of repeating the same combination again would take 32 years... I think you will agree that 24 bits are more than enough to ensure good security for this project! Up to eight tags When setting up the system the user can make the system learn up to eight separate tags. The unique code of each of the tags is then stored in memory. When a tag is detected the micro compares its code with those in memory. If a match is found the relay is latched for one second and the GO led is lit also for one second. One of the eight user LEDs will also light to indicate which tag was detected. After the relay unlatches, the system goes back to standby, waiting for the next tag to come by. That is really all there is to the system. The relay can be used to operate an electric door strike to give controlled access to a room or building. Be careful when selecting the strike: you can get “fail safe” where the lock The heart of the project is this RFID module, which comes pre-assembled and tested, ready to solder into the PC board. November 2010  45 BR1 W04 REG1 7805 +5V KEY LED14 A LEARN  K 560 LED1 100 F  K 100nF 4 14 560 Vdd RB1 RA0 RA7 17 330 6 RB0 RB5 RB4 +5V 26 [PIN NOS ON RFID MODULE ARE NOT MARKED BUT PINS ALIGN WITH HOLES IN PCB] 1000 F 25V CON2 ~ RA2 10k RA3 3 RB2 RA4  S2 Vss RB3 K USER 2 LED3 K  A  USER 3 K USER 4 LED5 K  A K  10  A 1 A ERROR LED13  K A A 560 560 K DETECT 8 9  A CON3 560 LED11 2 NC COM NO USER 8 LED9 K A USER 7 K LED10  D1 1N4004 USER 6 LED7 K RLY1 K USER 5 LED8 11 A NO GO SELECT USER 1  A LED6 RB6 1 K 15 IC1 RB7 PIC16F628A 12 28  LED4 16 A 13 A 16 4 RA6 S1 RFID MODULE 100nF LED2 MCLR 18 A RA1 LEARN 27 IN GND POWER IN – 10k 100 15 + 10k 7 SENSING COIL (PREMADE) OUT A ~ 10k B C E GO  LED12 Q1 BDX37 K 560 5 GND SC 2010 RFID SECURITY SYSTEM K K A LEDS A B 1N4004 C BDX37 E IN GND OUT 7805 Fig.2: the RFID module detects any tag brought into close proximity, sending its code to IC1. This in turn determines whether it is a valid code and if so, energises the relay for about a second. The one-second relay closure is perfectly suited to a central locking controller, or an electric door strike, such as this one (available from Jaycar and Altronics). Bear in mind our comments about fail-safe and failsecure electric strike models. 46  Silicon Chip will be open if power is not applied, or “fail secure” where the mechanism will be locked if power is not applied. You have the choice of wiring the relay output so power is normally applied and the lock opens when the relay pulls in (wasteful of power but important if emergency egress is required) or using a fail-secure strike which “opens” for the second power is connected (much less wasteful of power but can be a hazard in an emergency). The digital output from pin RB2 can be interfaced to an existing security system so that the RFID system can trigger it, turn on lights and cameras, sound a warning siren and so on. Just keep in mind that the relay only pulls in for a second, so any other device will need to take this into account. As the system will operate on 12V DC it can be used to operate a car central locking system. The scanning coil could be placed up against the inside of the windscreen and the relay connected to the car’s locking system. This would give a high level of security to your vehicle. I’m sure that readers will come up with a few other applications for this system. Indeed, the 8-user LED outputs can also be used to perform various functions – with some clever interfacing the eight user LEDs can be used to give varying levels of security. As an example, user 1 may be given full access to a secure building. Users 2 and 3 may only be allowed access to certain rooms. Despite its apparent simplicity, the project presented here could form the basis of a very secure personnel access control system. How it works The circuit diagram shows that there are not a lot of components in siliconchip.com.au (TO COIL) 560 560 10k 560 100 10k 560 560 S1 10k 330 S2 NO NC C BDX37 5 CON3 RLY1 100nF BR1 – ~ IC1 PIC16F628A ~ 100 F K291 + + © oatleyelectronics.com 1000 F LED14 LED1 LED13 LED12 LED11 LED10 LED9 LED8 LED7 LED6 LED5 LED4 LED3 KEY LEARN NO GO GO REG1 7805 POWER 4 D1 + 3 10k 100nF 2 Q1 CON2 16 15 CR003 560 SELECT 1 LEARN MODULE 4004 RFID 28 27 26 LED2 USER USER USER USER USER USER USER USER DETECT ERROR 8 2 1 7 6 3 4 5 Fig.3: follow this component overlay as you construct the RFID Security System. Note LED 14 faces the opposite way to the other LEDs. We suggest you use an IC socket for the PIC processor, as seen in the photo below, as it makes checking simpler. PARTS LIST – RFID Security System 1 PC board 96 x 62mm, code K291 1 CR003 pre-built RFID receiver module (supplied with pre-made sensing coil to suit) 1 2-way PC-mount screw terminal, 5.08mm spacing (POWER – CON2) 1 3-way PC-mount screw terminal, 5.08mm spacing (RELAY OUT – CON3) 1 SPDT 12V relay, PC-mounting 2 tactile switches, PC-mounting 1 18-pin DIL IC socket Semiconductors 1 PIC16F628A microprocessor (programmed with RFID_4.hex) 1 7805 5V three terminal regulator 1 W04 bridge rectifier 1 BDX37 NPN transistor 1 1N4004 silicon diode 14 5mm LEDs of any colour Capacitors 1 1000µF 25V electrolytic 1 100µF 25V electrolytic 2 100nF monolithic.................... (code 104 or 100n) Resistors (0.25W, 5%) 4 10kΩ (R3,R6,R7,R11).......... [brown-black-orange-gold] 6 560Ω (R1,R5,R8,R9,R10,R12)...[green-blue-brown-gold] 1 330Ω (R2)...................... [orange-orange-brown-gold] 1 100Ω (R4).......................... [brown-black-brown-gold] WHERE DO YOU GET IT? this system – if we take away the mandatory power supply there is not much left. The actual receiving of the data is done by a pre-built module. The output from this module is a 42-bit data frame but as explained above we only use the last 24 bits. The micro extracts this 24-bit data, then compares this with the eight memory locations and if a match is found the relay is latched for one second and the activated user LED is turned on for 1 second. The ERROR LED will light if a tag was detected but its code was not complete or corrupted in some way. The DETECT LED lights to show a tag was detected and decoded. The power supply is about as standard as you can get, with a bridge rectifier followed by the standard big filter capacitor, 3-terminal 5V regulator and then a 10µF output filter capacitor. The two 100nF caps help to keep the supply rail quiet and are placed near the microprocessor. Pushbutton switch S1 and associated components, along with the learn LED, are used in the tag storage function. Pin 7 (RB1) can be both an input and an output. Normally the pin is an input and the learn LED is off. The micro polls this pin looking to see if the push button PB1 is pressed at any time. When it is pressed the input pin is changed to an output which is then pulled low. What this does is to hold the learn LED on after the button is released. This siliconchip.com.au This design and its operating software are copyright © 2010 Oatley Electronics. A kit of parts for this project, with all components listed above, is available from Oatley Electronics (Cat K291). www.oatleyelectronics.com or (02) 9584 3563, for $40 including 10 keyring RFID tags. Extra tags are $1.50 each. Any technical enquires for this project should be directed to jeffmon<at>optusnet.com.au Phone support is not available for this project. All enquires and questions will be answered via this email address within 48 hours (most will be answered within 12 hours). now means that the system is in learn mode. Learning the tags Before this system can work effectively it must learn at least one tag so that it will have something to compare any detected tags with. To learn tags the operator presses and releases the learn button. The learn LED will now come on and stay on as previously stated. The program is now in learn mode and waiting for the next tag to come along. The operator now simply places the tag to be stored near the receiving coil. If the program successfully decodes this tag the learn LED will go out and user 1 LED will come on. The system is now waiting for the user to select a memory location for the next tag. November 2010  47 Pressing the USER SELECT button will cause the user LEDs to cycle around. First press will turn user 1 LED off and user 2 LED on. Next press will turn user 2 LED off and user 3 LED on. Each press of the select button will shift along the LEDs. When LED 8 comes on the next press will cycle back to user 1 LED. When you are happy with the memory location press the learn button again. The last decoded tag will now be stored in the memory location indicated by the user LEDs. The LEARN LED will now flash once. The program now stores the unique tag ID in EEPROM. That’s it, the tag has been saved. When the same tag is decoded next time the system will respond and allow access to the user holding that tag. To erase any memory location the operator simply goes through the same procedure and stores the new tag over the top of what was stored in the old memory location. To summarise the tag learning procedure users should consult the following table: ACTION RESULT Press and then release Learn LED on the LEARN button Bring required RFID tag in range of coil Learn LED off User 1 LED on Select memory location with SELECT button User LEDs shift along When location selected press LEARN button Tag stored in user location The Tag has now been detected, decoded and stored in the User EEPROM location. Construction Assembly of the project is fairly straightforward. The PC board is of a very high quality so as long as your soldering is up to the task and the components are placed in the correct position you are virtually assured of an operational project. Start with the resistors and capacitors. Remember that the electroylitic capacitors are polarised so be careful when installing them. The same goes for the LEDs. There is a trap for young players with the LEDs: all bar one mount flat side (cathode) to the right, when looking at the board with the terminal blocks on the right. LED 14 mounts 48  Silicon Chip The sensing coil (shown close-up at right) solders directly to the PC board alongside the RFID module. This coil, which measures about 50 x 45mm, is made from very fine wire so needs to be treated with all due care. The ends of the coil wires pass through a protective spaghetti sleeve to protect them. cathode to the left. You have been warned! It is recommended that an IC socket be used for the microprocessor – again, this must go in the right way around. The RFID module should be installed next and again be careful when handling this component. The bridge rectifier, 3-terminal regulator and transistor are next and all three are polarised (no heatsink is needed on the regulator). The relay is the last on-board component and will only go in one way. Sensing coil The sensing coil is supplied preassembled, which means you only need to attach it to the PC board. However, the wire which forms the coil is quite fine and will be easily damaged with any form of rough handling. There’s about 200mm of wire emerging from the coil – this attaches to the two points marked “COIL” on the PC board (polarity is unimportant). To protect this fine wire, we slid on a piece of thin heatshrink tubing over the two wires (which are in fact loosely twisted together) and glued it to the coil itself (the coil is actually quite rigid). To prevent stress on the opposite ends of these wires (ie, the end where they solder to the PC board), we anchored the heatshrink with a small cable tie right around the RFID module and heatshrink You also need to decide whether you’re going to have the coil close to the PC board or some distance away. If you mount it any further away than the ~200mm allowed by the connecting wires, you’ll need to extend them with either thin insulated hookup wire or better still, two strands of ribbon cable or some thin Figure-8 cable. Note that we have not tested the RFID unit with the coil any further away than the 200mm. In theory, it should be quite OK but . . . Smoke test At this stage do not install the microprocessor. Apply power and using your multimeter measure the voltage on pin 14 with respect to pin 5 of the micro. You should read close to 5V DC. If OK, then switch off the power, wait for a short while and then install the microprocessor. This time when you switch on the power the LEARN led should come on for 500ms. If this happens then the system is alive and well and ready for work. One of the first things the program does is to load the eight user IDs from EEPROM so it is ready to decode the stored tags. If no user data has been stored in EEPROM the unit will ignore all tags. Go through the learning tag procedure to store at least one tag. SC ELNEC IC PROGRAMMERS High quality Realistic prices Free software updates Large range of adaptors Windows 95/98/Me/NT/2k/XP CLEVERSCOPE USB OSCILLOSCOPES 2 x 100MSa/s 10bit inputs + trigger 100MHz bandwidth 8 x digital inputs 4M samples/input Sig-gen + spectrum analyser Windows 98/Me/NT/2k/XP IMAGECRAFT C COMPILERS ANSI C compilers, Windows IDE AVR, TMS430, ARM7/ARM9 68HC08, 68HC11, 68HC12 GRANTRONICS PTY LTD www.grantronics.com.au siliconchip.com.au