I wanted to make an easy and secure way to enter my garage. RFID was the best way to unlock my door, even with my hands full I can unlock the door and push it open! I built a simple circuit with a basic ATMega 168 arduino chip and a ID-20 RFID reader to control an electronic door lock.
The circuit consists of 3 separate parts, a Reader to read RFID tags, a Controller to accept data from the reader and control the output of the RGB LED and the Electric door lock. The door lock is first installed in a door and tested with a 9v battery to ensure correct installation. In most cases you want a Normally Open circuit on the door lock, or Fail Secure. This means the door stays locked when no current passes through it. When 12vDC is passed through the electromagnet in the door lock, a plate in the lock gives way and allows the door to be pushed open freely.
The reader is placed on the outside of the door and is separate from the controller on the inside so that no one can circumvent the security by breaking open the Reader and trying to short circuit the reader. The controller receives serial data from the Reader and controls the RGB led and the Door lock. In this case I have put both on separate bread boards for testing. Here is a video overview of the system in action Read on to see how to build one for your self!
All of the code, schematics, and PCB designs have been tested and refined. They are all posted here as of 8/9/2010
Updated video of the final system installed and working.
Step 1: Parts Needed
ATmega168 with Arduino Bootloader $4.95
Crystal 16MHz $1.50
Capacitor Ceramic 22pF $0.25 (x2)
Resistor 10k Ohm 1/6th Watt PTH $0.25
Mini Push Button Switch $0.35
Triple Output LED RGB - Diffused $1.95
Either one of these, 20 has better range, 12 is smaller
RFID Reader ID-12 $29.95
RFID Reader ID-20 $34.95
RFID Reader Breakout $0.95
Break Away Headers - Straight $2.50
RFID Tag - 125kHz $1.95
TIP31A transistor (radio shack/local electronics store $1.50)
Door Lock is from ebay.
Door Fail Secure access control Electric Strike v5 NO $17.50 (kawamall, bay)
Step 2: Build the Arduino controller
The hardware portion of this RFID reader would be too simple if we used a regular arduino with built in USB programmer. Since I plan on putting this into the wall and not touching it again I dont want to use a big bulky $30 arduino board when I can buy a $5 ATMega 168 and make a much smaller custom PCB.
Because I chose to make a basic Arduino circuit myself I need an external USB->Serial FDIT programmer. I have included Eagle schematics of the controller with a power supply built from a 7805 voltage regulator. In testing I used a bread board power supply.
To get an arduino up and running all you really need is the ATMega168 with the arduino software flashed on it, 2x 22pF capacitors, 16mhz crystal, 10k ohm resistor, push button and a breadboard. The hookup for this is well known but I have included the entire schematic for the circuit.
The arduino is going to trigger 4 outputs, 1 each for Red/Green/Blue LEDs, and 1 to trigger the TIP31A to send 12vDC to the door lock. The arduino receives serial data in on its Rx line from the ID-20 RFID reader.
Step 3: Build the RFID Reader
To build this, we are going to send 5v/Ground over from the primary bread board to a secondary bread board we are building the Reader on. Also send over 3 wires from 3 of the arduino output pins to control the RGB LED, one for each color. One more wire, Brown in the pictures, will be a serial connection for the ID-20 to talk to the arduino's Rx serial input. This is a very simple circuit to connect. LED's get resistors and a few points on the ID-20 are tied to ground/5v to set the correct status.
To make it easier to breadboard the ID-10/ID-20 Sparkfun sells a Breakout board that allows you to attach longer pin headers that are spaced to fit a bread board. This part and the pinheaders and listed in the parts list.
The schematic should be strait forward and easy to follow.
Step 4: Program!
You can easily upload my code to your arduino and never look back but whats the fun in that? Let me explain the basic idea of how it works.
First of all, I did not want any external buttons/switches/etc and I did not want to reprogram the arduino every time I wanted to add a new card. Therefore I wanted to use only RFID to control the operation of the circuit as well as control over the door lock.
The program turns on the Blue LED to indicate it is ready to read a new card. When the card is read it decides if it is a valid card or not by comparing what it read in to a list of valid cards. If the user is valid, the arduino turns OFF the Blue LED and turns on the Green LED for 5 seconds. It also turns on another output high for 5 seconds. This output is connected to the TIP31A transistor and allows the tiny arduino to control a much larger 12v 300mA door lock without being damaged. After 5 seconds the door lock re-locks and the LED turns back to blue to wait for another card to be read. If the card is invalid then the LED changes to RED for a few seconds and back to Blue to wait for another card.
It is important that the door lock still work even if the arduino loses power overnight or is reset. Therefore all valid card ID's are stored in EEPROM memory. The ATMega168 has 512 Bytes of EEPROM memory. Each RFID card has a 5 Hex Byte serial number and a 1 Hex Byte Check sum that we can use to verify there were no errors in the transmission between the ID-20 and the arduino.
Valid cards are stored in the EEPROM by using the first Byte as a counter. For example, if there are 3 valid cards stored the first Byte in the EEPROM would be 3. EEPROM.read(0); = 3. Knowing this, and the fact that each ID is 5 Bytes long we know that 1-5 is card one, 6-10 is card 2 and 11-15 is card 3. We can make a loop that looks through the EEPROM 5 bytes at a time and tries to find the card that was read in by the reader.
But how can we add new cards to the EEPROM after the circuit is installed?? I have read in one of the RFID cards I have and hard coded it to be the Master RFID card. So even if the entire EEPROM is wiped the master card will still function. Whenever a card is read, it checks first to see if it is the Master card, if not, then it continues to see if it is a valid card or not. If the card is the master card we have the arduino go into a "programming mode" where it flashes RGB and waits for another valid tag to be read. The next tag that is read is added to the next free spot in the EEPROM and the counter is incremented 1 if the card does not already exist in the EEPROM memory. The reader then returns to normal mode and waits for a new card to be read.
Currently I have not programmed a way to delete a card as the reasons for deleting a card would most likely be it was lost or stolen. As this would most likely be used with 1-10 people the easiest thing to do would be to hard program a Master Erase card that will wipe all cards from the EEPROM then re add them all, which only takes a few seconds. I have added code to wipe the EEPROM but I have not implemented this feature yet. .
The code is attached in a text file along with a copy of the parts list.