RFID Object Locating System: Design, Construction, and Functionality, Study Guides, Projects, Research of Electrical and Electronics Engineering

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RFID Personal Object Tracking Device

Final Paper

by

Bo Li John Rhine Naixing Wang

Spring 2008 ECE 445

TA: Purvesh Thakker Team 23

Abstract

We designed and constructed an object locating system using RFID. The system consists of two distinct parts: a static system which will allow the user to locate from long range the object they would like to track and determine which room it is in and a mobile system that allows the user to use once they get into the room.

The static system consists of the RFID Reader and the wireless components with the transmitter and receiver. The user will turn on the RFID reader, which will read all the tags that are within a given range. The reader will then send the important parts of the tag IDs to the transmitter, which sends them to the receiver. Upon receiving the correct bits to start, the receiver will light up the correct LED that corresponds to the object connected to the tag that was found.

The mobile system consists of a remote and a base. The remote will send the signal that the base will receive. If the base receives the signal, it will power the buzzer, allowing the user for quick detection of the object.

For verification purposes, we tested the reader for range, the accuracy of the transmission for the wireless part, and the range and battery life for the mobile system.

• 1.1. Purpose 1. Introduction
• 1.2. Objectives 5-
  • 1.2.1. Goals
  • 1.2.2. Functions
  • 1.2.3. Benefits 5-
  • 1.2.4. Features
  • 1.2.5. Specifications 6-
    • 1.2.5.1. Mobile System
    • 1.2.5.2. Static System
    • 1.2.5.3. General
• 1.3. Subprojects 7-
  • 1.3.1. Hardware Block Diagrams
    • 1.3.1.1. Mobile System
    • 1.3.1.2. Static System
  • 1.3.2. Mobile System Description
    • 1.3.2.1. Remote
    • 1.3.2.2. Receiver
  • 1.3.3. Static System Description
    • 1.3.3.1. RFID Tags
    • 1.3.3.2. RFID Transmitter
    • 1.3.3.3. Transmitter-315-LC
    • 1.3.3.4. Receiver-315-LC
    • 1.3.3.5. PIC
    • 1.3.3.6. LED Display
• 2.1. Mobile System 10- 2. Design
  • 2.1.1. Description
  • 2.1.2. Schematic
  • 2.1.3. Alternatives 10-
• 2.2. Static System Wireless 11-
  • 2.2.1. Description 11-
  • 2.2.2. Transmitter Schematic
  • 2.2.3. Receiver Schematic
• 3.1. RFID Reader 3. Software Flowcharts
• 3.2. Static System Transmitter
• 3.3. Static System Receiver
• 4.1. RFID Reader 4. Design Verification
• 4.2. Static System Wireless
• 4.3. Mobile System 17-
• 5.1. Labor 5. Costs
• 5.2. Parts
• 5.3. Total
• 6.1. Successes 6. Conclusion
• 6.2. Challenges
• 6.3. Next Steps 20-
• 6.4. Ethical Considerations
• 7.1. Pictures 22- 7. Appendix
• 7.2. Component Data Sheets 24-
• 7.3. Code 25-
• 7.4. References

1. Introduction

1.1 Purpose

We believe that our project has a very practical and necessary use. A lot of frustration and time is spent on locating commonly important but lost objects such as keys, remotes, or wallets. Many people would appreciate integrating such a tool in their everyday lives. RFID is a technology that is rapidly growing. We were very excited to implement our solution using RFID. It gave us the flexibility to create two structures, one static and one mobile. Also, being able to track individual objects using relatively non-obstructive and small means is a bonus.

1.2 Objectives

1.2.1 Goals

The main goal of our project is to develop an (eventual) marketable product that will allow for easier locating of everyday used objects. We feel like our idea is an improvement on any of the products in the market currently and will provide an increase in the quality of life for the consumer. Academically, the goal of this project is to learn more about RFID technology and how to develop a product from start to finish.

1.2.2 Functions

There are two main functions for the RFID personal object tracking device. First, we want the user to be able to know the general vicinity of their lost object and second, we want the user to be able to find it rapidly without getting frustrated. In order to do this, we created separate devices for each function.

First, the objects are sent into a central location, which could be a wall mounted device located anywhere in the house. From this device, a user will be able to see which room any of their objects with the RFID tag are located. In order to help the user find the specific object, we will create a separate handheld tracking device that will be able to detect how close or far an object is from the person. We anticipate the user first looking in the central location to determine the room and then using the tracking device to determine the specific location.

1.2.3 Benefits

 The users would never be without important personal objects such as their keys, which if lost would prevent them from entering their own homes.  Money saved from replacing important objects.  Small and compact design of receivers and size of transmitters for easy and convenient integration into the user’s life.  Countless time and frustration saved from trying to locate missing objects.  Complete easy and fast coverage of the entire house with the static receivers.  Mobile transmitter provides for portability and affordability

1.2.5.3 General

Table 3 General System Goals vs. Actual Goal Actual Software executes <1 min. Software executes almost immediately RFID tags must be able to withstand weather conditions

This was never fully implemented

System start up time of <1 min System starts up almost immediately Capable of handling at least 3 different objects

Capable of handling up to 7 different objects

1.3 Subprojects

1.3.1 Hardware Block Diagram

1.3.1.1 Mobile System

Figure 1 Block Diagram of Mobile System

1.3.1.2 Static System

Figure 2 Block Diagram of Static System

1.3.2 Mobile System Description

1.3.2.1 Remote

The remote will contain a transmitter a push button, and an antenna. The user will use the push button to power the transmitter and send a signal to the receiver.

1.3.2.2 Receiver

Remote Transmits Signal

Receiver Receives the Signal

Buzzer Sounds to Indicate Device Found

Read RFID Tags

Send Tag ID to the Transmitter

TXM- 315 - LC

Transmitter

RXM- 315 - LC

Receiver

PIC LED Display

This piece of the mobile system contains a receiver chip, an antenna, and a buzzer. It will get the transmission of the remote and will send a high output to the buzzer. The buzzer will indicate where the object is and allow the user to find the object quickly.

1.3.3 Static System Description

1.3.3.1 RFID Tags

Small RFID tags are attachable onto personal objects. These are used to identify the object through RFID technology. The PIC will send a command for the reader to read for tags. Each tag sends the reader its unique serial number. This can be used to determine which object is present.

1.3.3.2 RFID Transmitter

Once all the items have been identified, the tag for that object is set to 1. The reader sends all the tags that have been sent to 1 to the transmitter so that it can then be received by receiver.

1.3.3.3 TXM-315-LC transmitter

The TXM-315 transmitter is a wireless communication device that sends data to a receiver. It operates at 2.1 Ghz, and has a state theoretical range of about 300ft and requires a 5V power supply. This transmitter will be used to communicate between a RFID transmitter in a room, and the LEDs, because a wireless system should not need wired connections over a long distance between rooms.

1.3.3.4 RXM-XXX-LC receiver

This takes the data from the transmitter and sends it to the PIC. Like the transmitter it operates at 2.1Ghz and has a theoretical range of 300ft. It will send data displaying what is in each room, by sending the unique object ID.

1.3.3.5 PIC

A programmable microprocessor will run the static system. One PIC is needed for the display unit, and one is needed for each room transmitter. The PIC in the display unit will collect data from the wireless transmitter and display it on the LEDs. The PIC for each transmitter will be used to collect data and then pass it to the wireless transmitter.

1.3.3.6 LED Display

Figure 3 LED Dimensions Figure 4 LED Display

10.16 mm

8 mm

25.27 mm

contained within a remote for the user, providing plenty of space. Also, it does not draw battery power until the user turns it on. The transmitter is powered by a 9 volt battery that is regulated with a 5 volt voltage regulator. We use a LINX TXM-315-LC transmitter to transmit a high signal to the receiver when it is turned on. We have a simple switch in the form of a button that the user pushes when they want to turn the system on and send a signal to the receiver. The receiver uses the same 9 volt battery and 5 volt regulator to power it. We use a LINX RXM-315-LC chip to receive the signal from the transmitter. There is a data bit connecting to a buzzer that is turned on when the bit is set to high. We chose these chips because they have a theoretical 300 ft range, which is sufficient for the audio level from the buzzer (even though the actual observed range is less). The circuit at the moment is very simple, but the receiver only has a predicted battery life of around 42 hours. Even though this lacks the benefits of a passive ID tag for the receiving side, this is more compact than a design that would include an RFID reader and much more cost effective to produce.

2.1.2 Schematic

Figure 5 Schematic of mobile system

2. 1. 3 Mobile System Alternatives

Our original design included an RFID reader with a directional antenna. It would still use the wireless chips that we are using, but the output would be on the transmitting side via a bar of LEDs. Since the directional antenna would detect if the remote was pointed towards the object, but not the signal strength, the LEDs would be used to represent how many tags it detected. The benefits of the original design is that it uses passive tags, which is more power efficient than our current design. However, this is overshadowed by the fact that the RFID reader would increase the cost of producing this product significantly. This would lower its practicality in the household, seeing that most people would not pay that much money to locate their keys. Also, the reader would add significant size to the remote. After some research on a previous group that developed a product to track birds, we came up with some ideas we could use for our project. They used a Linx HP3 Transmitter and

LINX HP3 Receiver for their project. We use whip antennas which measure the distance they operate by using this equation:

L = 234/FMHZ Where L = length of feet of quarter-wave length.

The frequency of the HP3 series is 902.62–927.62 MHZ. The frequency of the LC series is 315–MHZ.

The HP3 has a higher operating frequency. Therefore with the same antenna and battery source, the HP3 is going to have a longer range.

Also, the group that tracked birds used a smaller battery with lower voltage. Their choice was a lithium 3.6 volt battery, which is almost three times less than our 9 volt battery. The tradeoff with this choice is more battery life in exchange for distance covered. However, with their higher operating frequency, it seems that they covered the same amount of feet we did with our LC chips and a 9 volt battery. Switching our chips and battery would provide for longer battery life as well as a more compact design. However, the main reason for their one month battery life success is due to reasons we cannot incorporate into our design. Their transmitter was on their bird and was turned on by the accelerometers. Their receiver was with the user. In our design, our transmitter was with the user. The power on or power off status of the transmitter is easier to control, while the receiver requires a manual user to power off the device. There is no way we can put a transmitter on the lost object, because there would be no cases we could design to turn the transmitter on. The transmitter would always have to be on, which causes the same battery issues that we are currently experiencing. Overall, incorporating parts of their design into ours would improve our product. A PCB board, combined with the smaller battery would greatly improve the space we currently use for our receivers.

2.2 Static System Description

2.2.1 Static System Description

The RFID reader we finally settled on was a SkyeModule M9 reader. This reader has an operating frequency of 862-955 MHz, and works with a variety of standardized tags. It has configurable power output, as well as several data output options. It has the capacity to read multiple tags at one time, as well as store tags in memory until a command is given to read those tags out or to delete the collection of tags. This made it attractive for our purpose. Its range though is somewhat limited with the ability to read a single tag from 120 cm away if the antenna is properly positioned.

The wireless system included two LINX LC chips. The transmitter was connected to a PIC16F877A, which was operated by a 20MHZ crystal oscillator. There was one data bit feeding from the transmitter to the PIC. The transmitter chip is connected to a whip style monopole antenna. The antenna must be placed above a ground plane. This antenna is omni directional with a small blind area in the radiation pattern right above the antenna. The receiver is connected to a PIC16F877A with a 20MHZ crystal oscillator to match the frequency. There is a data bit from the receiver that feeds into the PIC. The PIC controls an LED bar, which lights up when the appropriate objects are detected. We also used a 47k resistor that hooked

Figure 7 Schematic of Receiver in Static System

3 Design

3.1 RFID Reader

Figure 8 Flowchart of RFID Reader

3.2 Static System Transmitter

Figure 9 Flowchart of Static System Transmitter

3.3 Static System Receiver

4.1 RFID Reader

The RFID testing consisted of several parts. The first test was to determine a rough radiation pattern of the reader while connected to the antenna. In order to do this we set the reader into a state where it outputs the tag ID whenever it is read. We then moved tags closer to the antenna until the reader output the tag ID. We tested the distance from the reader as well as the orientation.

The second necessary test was to test the anti-collision system of the reader. If a tag was too close in proximity the reader does not have the ability to read both. So we tested the tags in various arrangements. We attempted to read tags that were in a stack, a random pile, side by side, and staggered. We also tested the distance between tags when the collision error happened.

A final test was to determine whether the system has hysteresis, or a path dependence. We tested this by comparing the range depending on if the reader had already found the tag. We took the tag and placed it near the reader, and slowly increased the distance, then recorded the distance. We then moved the tag closer and compared the ranges. We found no hysteresis effect in the system whatsoever.

Figure 11 Output of command to read a tag

Table 4 Range of Detection of Tags From Different Locations Around the Reader

4.2 Static System Wireless

Figure 12 Testing of the LED1 after the transmitter has sent the signal

4.3 Mobile System

The testing for the mobile system consisted of the range of the system under various conditions as well as the battery life. In our first test, we measured the distance that the mobile system was operational with and without interference. As predicted, the range of the mobile system decreased with more interference. Even though our transmitter has been measured at 300 feet, the maximum range that we could detect the signal was 150 feet. The lowest range we could detect was through a door, which nearly cut the range in half.

Table 5 Range of Mobile System at Various Ranges

The next test we ran involved the predicted battery life of the transmitter and the receiver. We know that a standard 9 volt battery has a battery life of 500 mAh. We measured the current draw of the transmitter and receiver while both were on and detected a draw of about 12 mA for both circuits. Using the equation

Battery Life = (Total mAh) / (Current Drawn)

We determined that the battery life on the transmitter and the receiver is approximately 40 hours. This would mean that the battery would only last about two days, which is not nearly enough time if this product were to be marketed. Table 6 Predicted Battery Life of the Transmitter and Receiver

Transmitter

LED

5.1 Labor

Bo Li: ($50/hour) x 2.5 x 130 to complete = $

John Rhine: ($50/hour) x 2.5 x 130 to complete = $

Naixing Wang: ($50/hour) x 2.5 x 130 hours to complete = $

Total Labor Cost = $

5.2 Parts

Table 7 List of Parts

Name Quantity Cost Total Cost

RFID Tags 5 $2.50 $2.

Skyetek Reader M9 1 $400 $400.

TXM- 315 - LC 2 $32 $

RXM- 315 - LR 2 $32 $

PIC16F877 Microcontroller 3 $10 $

MAX232 1 $1.70 $3.

Power Supply 1 $30 $

9V Battery 2 $5.00 $10.

166 × 55 × 10 mm Breadboard 3 $10 $

MV57164 LED Bar 1 $2.95 $2.

1 uF capacitors 8 $0.50 $

Miscellaneous (20 MHz Crystal Oscillators, etc)

Total Cost $ 56 6.

5.3 Total Cost

Labor + Parts = $48750 + $566.85 = $49316.

6. Conclusion

6.1 Successes

Many of the parts of our project worked successfully. The RFID Reader, the wireless components of the static system, and the mobile system all work perfectly. We can get the reader to correctly read, identify the tags, and output it to the computer using Hyperterminal. We can get the wireless component to take an output, and transmit the correct tag number to the receiver. The receiver then takes the transmitter output and lights up the correct LED corresponding to the tags that were read. The mobile system correctly transmits when the user presses the switch and the receiver corrects picks up the signal and outputs the high to the buzzer.

6.2 Challenges

However, we ran into a number of issues when combining the RFID reader and the wireless components of the static system. Whenever we tried combining them together, we kept running out of memory (RAM, ROM) on the PIC. Since the reader did not simply cycle through tags and find all of them, and instead seemed to find random tags, we needed to loop through the code many times to try and find all the tags that were close to the reader.

We were also very slow to switch readers after the initial TI reader we were using did not work for us. Without much time, we were not able to figure out a structure to code the reader to interact properly with the wireless devices.

However, through this entire process, we learned a lot about how to manage a project from beginning to end and learned a lot about how to work as a team. Beyond the lesson of switching hardware if one is not suitable, we also learned that it can be very important to implement the simpler parts of the project first. In our case, it would have been much more advantageous to work on the mobile system first. These small victories would have provided some momentum and excitement for the rest of the project.

We also learned a lot about how to function on a technical team together. With the expertise that all three of us brought to the group, we were able to accomplish things that we would not have been able to accomplish without each other.

6.3 Next Steps

In order for this project to become more marketable, we need to make several improvements. We would ideally like to use the long range readers instead of the short range one to get better idea of what room the object is in. Also, we would like to implement the LCD display for the static system instead of the LED display in order to provide a more user friendly display that gives better directions. Another change in the static system that we make is to have each reader send out a different start packet string. This will allow the central reader to determine which of the readers was picking up the object to determine which room the object was located in.

For the mobile system, we will need to implement a system similar to the one used by