This shield could be used as a stand-alone transponder key, or with Google’s servers to create a cloud-computing application.
It’s time to present you an application with RFID. We want to show you how to use the popular Arduino to produce a device capable of recognizing passive transponder (TAG). But this is not the usual RFID key, because the system can activate a relay if a recognised TAG is read, but also we took the opportunity to make an application that use cloud-computing. The basic version, which is a simple key relay consists of an Arduino (Duemilanove or UNO) and the RFID shield based on a ID-12 of ID Innovations: placing a transponder already learned, the relay is activated.
The extended version of our project uses an Arduino, the RFID Shield and the Ethernet Shield with which we can access the Internet and stored, using the Google Docs service, the transponder data.
The RFID shield
But before you see the applications in detail, we spend some words on the shield for Arduino that we need to capture data of passive TAG. It is a very simple circuit based on the form ID-12 , which contains a complete recognizer of passive transponders, in addition to a relay controlled by Arduino and a few other passive components. The buzzer, which allows you to set an audible alert, could be controlled by ID-12 or by Arduino.
|Figure 1.||ID Innovation ID-12 RFID module pinouts.|
|Figure 2.||RFID shield schematic diagram|
The relay is powered by Vin Arduino (and the corresponding contact of the shield) and GND. The base of the transistor that controls RL1 is driven by the pin 9 of the Arduino. The lines 6 and 8 control the lighting of the LEDs. In our case, the pin 7 of ID-12 is connected to ground, so the chip will only recognize ASCII coded tag and return its output in ASCII characters.
The component has a TTL level serial interface, accessible from it’s pins 9 and 8, then there is an output (pin 10) that pulses rapidly (at a frequency of 3 kHz) every time the module detects the code of a tag encoded and used to drive a buzzer or a light emitting diode.
All data are read from Arduino using the library NewsoftSerial that allows to emulate a serial port; in our case, the emulation is carried on lines 7.
How it works
Once you put power to the system, when the module ID-12 reads a tag, the pin 10 pulse at 3 kHz and the Arduino read s data; then microcontroller compares the code with those who has in memory. If the transponder is one of those already learned the micro actives the relay and the green led. This relay will be used to control an electric lock, a gate, etc..
In bistable mode, the relay changes state each time the ID-12 reads a valid tag. Clearly, the circuit can work well if in his memory there is at least a RFID tag.
To learn the code for a tag and then write it to EEPROM, you must press and hold button P1 for 3 seconds (max. 5), once that is done you have to pass a card and wait for the confirmation sound (given by buzzer) and light (provided by the green LED).
At any time you can remove a tag code from memory: must press the P1 button for 5 seconds or longer, until the red LED lights on. At this point you release the button and pass the tag to be deleted, if the LED turns off and on again, the card has been deleted.
To erase the entire EEPROM you must restart the Arduino, and during the reboot, hold down the button P1 for about one second; when the red LED lights up. Done this, Arduino is ready to read new tags.
Source Code - download