Low-Cost Radio Frequency ID Readers
Although there is great potential for Radio Frequency Identification (RFID) technology to benefit the study of birds and other wildlife, the cost of RFID systems can be prohibitive to those with a very modest research budget. To those researchers, we offer our design for a low-cost RFID data logging system that can be used in association with birdfeeders, nest boxes, or anywhere birds may congregate, to monitor the activity of individual birds bearing RFID tags. These readers can be constructed for as little as about $15 to $40 per unit depending on the effort expended by the user as opposed to an electronics manufacturer.
The photo to the left shows an RFID-logging unit attached to an inexpensive birdfeeder. The box at the bottom of the feeder houses both the reader circuitry and the power supply (in this case an array of AAA batteries). The red and black ring just above the box is an RFID antenna that reads the tag of any birds that perches on the feeder.
The heart of the RFID reader is the circuitboard shown to the right. The key components are a PIC microprocessor, a U2270B RFID module, an EEPROM memory unit, and a real time clock. In addition to what is shown below, the logger requires a 12-16V DC current source and a 1.35 mH loop antenna, both of which plug into the screw clamps at the upper right of the top of the board. Some sort of housing is probably also necessary (depending on the situation). For this reason, the board was sized to fit into the lid of a 180ml Lock-n-lock box (see photo above). See the materials list to see all of the components and potential vendors for them. Click here for building instructions.
When the logger is activated and put into log mode, the microprocessor periodically turns on the RFID reader which polls for a tag. If no tag is read, then the logger enters a low-power pause mode for a short period of time, before polling for tags again. When a tag is read, the reader stores the date and time along with the unique tag ID number. Both the poll time and the pause time can be adjusted to strike a favorable balance between reading effort and power consumption. The logger also allows users to specify a nighttime sleep mode to save power, and users can control how often the reader stores the same tag consecutively (thus, a bird that sits on a feeder for 5 minutes will not use up 100 lines of data). Setting parameters and downloading data are effected by a simple serial interface. For more details, refer to the user manual.
For those capable of programming a PIC microprocessor, it is possible to modify the reader to interact with its environment through sensors and actuators. There are holes for pin headers near the bottom corners of the circuitboard, which allow for access to several I/O pins on the microprocessor. Hence, with some some tweaking, it would be possible to add in a temperature or motion sensor or to incorporate a servo motor.