Otter RFID Antenna System (Electronics Project)

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The Illinois Prairie Research Institute requires a robust RFID antenna system in order to track the movement of river otters into and out of a pond. River otters have only very recently been found in significant number in the state of Illinois, and researchers would like to monitor otter behavior to determine their impact on the ecosystem.

Most commercial systems available that can read passive RFID tags from a great distance cost tens of thousands of dollars. The purpose of this project is to develop a viable system at only a fraction of the cost of a commercially available RFID antenna and receiver system.


Figure 1: Overall Block Diagram

Figure 1: Overall Block Diagram.

The antenna (ANT-G01E-30) is a commercially available rectangular loop antenna which operates at 134.2 kHz. The antenna will be powered by the RFID receiver unit. The antenna will send a signal to the PIT tags (TRP-RR2B-30) which will be the source of power for the tags.

Using the power transmitted by the antenna, the PIT tags in return will send the unique ID number back to the antenna. The antenna’s inductance must match the induction requirement of the RFM module to ensure that the antenna is in resonance with the RFM module. The antenna then sends the data received to the RFID receiver unit.

Figure 3: RFID Receiver System Data Flow

Figure 3: RFID Receiver System Data Flow.

This unit is the main power source for the antenna and RFID receiver using a 12V car battery. When motion is detected, the microcontroller signals the power supply unit to power the RFID receiver unit. To extend the battery life, a solar panel will be connected to the unit to recharge the battery.

Figure: 7 Schematic of MAX232N

Figure: 7 Schematic of MAX232N.

There will also be movements by other animals which can activate the PIR sensors, so the number of detections per day is estimated to be as high as 30. For each detection, the system will draw power for 30 seconds which means the system could be operating for as long as 1.75 hours every week. The max current draw for the RFM/CTL units is 300mA, and the max current draw for the MAX232N chip is 10mA, so the total current draw is 310mA


The microcontroller/data storage unit is the most critical part of the design. Specifically, the signal that the microcontroller sends to the MOSFET switch for 12V power supply is vital for power management and the longevity of the system without requiring replacement batteries. First, the microcontroller must be tested with the code developed for signaling the power supply when motion is detected.

Each sensor input will be toggled on the microcontroller, and the output signal that should be sent will be probed using an oscilloscope. The high output signal that is sent must be clear and any oscillations that can be interpreted as a false-positive must be avoided. The high signal voltage must fall between 2V and 4.5V, and any oscillations must not cause the signal to go outside this range


The primary ethical consideration is that the project does not harm the river otters or other animals. The enclosure must properly isolate the electrical components from the external environment, so that animals are not harmed. Furthermore, the enclosure for the system must be environmentally friendly and not introduce harmful elements to the ecosystem.

With the use of batteries, acid leakage is a potential concern, and so batteries must be isolated from the environment within a container. Another ethical consideration is properly crediting every source consulted as well as not falsifying the data gathered from testing..


Source: University of Illinois
Authors: Jinwoo Bae | Charles Huang | Sumsaamuddin Mohammed

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