EE495M – Mobile

Communication Project

RFID Team

Final Report

By

Bader AlDalali baldalal@purdue.edu

Shan Bai sbai@purdue.edu

Vivek Vijay vvijay@purdue.edu

Ben Chen chenh@purdue.edu

Due Date: December 12th, 2004

Executive Summary:

The RFID team has accomplished all the tasks they set at the beginning of the semester.

The tasks included interfacing a temperature sensor to the tag circuit, adding a switching

method to send data to the reader, retrieve data on reader and display temperature and I.D

data periodically.

The analog temperature sensor has been integrated with the tag circuit. An A/D converter

has been added to the sensor to output the 8-bit binary data. A PLD has been used to

convert the binary output into BCD data.

For the rest of tag circuit, two nine volt batteries have been used as power source to drive

the switch. The shift register circuit is implemented by timer, counter, dip switch inputs,

and the PISO shift registers.

For the reader, the final design included a few circuits. The circuit that provided the

clock had a 555 timer, with an edge detector, a counter, and a PLD that produces the

required clocking pulse. The second circuit included the shift registers, two PLDs that

latched the data, and the enable circuit. The third and fourth circuits included the 7-

segment decoders and displays for the ID and temperature data.

The main task for future teams would be to work on the RF data receiving range, the

speed of data transmission, and the of the circuit.

Delivery Project Summary:

The goal of this semester’s RFID project is to measure temperature data and transmits it

with I.D. data to the reader circuit, and displayed by 7-segment LEDs. The technique for

data transmission is by using amplitude modulation. This is accomplished by using a

switch circuit. The data are generated from temperature sensor, converted from an analog

output to parallel digital outputs, and transmitted by using parallel-in, serial-out shift

register to send the data through the switch circuit.

On the reader side, the original circuit reads the signal and converts it to digital signal.

The received BCD data is then shifted into the 7-segment displays and displays the

specific ID number with the corresponding temperature.

Reflection:

Ben Chen

This RFID project has been another great engineering project experience after completion

of senior design last semester. Through out the project, I have learnt additional

engineering experience in transistor theory and think of methods to implement

telecommunication theory into circuits. Most importantly, I have had a great time

working with my teammates, Bader, Sean, and Vivek. I am very grateful for the

opportunities to work together with them for the design, integration, knowledge sharing. I

would also like to thank Professor Krogmeier, Srinivas, and Foo; for providing us

recommendation and debugging for the design, and an experience closer to real world.

Sean Bai

Good project, good team, good effort, good experience.

Bader AlDalali

As an ECE senior this was the first project that actually gave me a hands-on experience

on present research projects. It also enabled me to utilize my background in ECE and all

the theories that I studied and thought were useless. This project also gave ma a chance to

work with such a qualified and hardworking team which includes the students, the T.A.’s,

and the Professor, and the success of our project was based on everybody’s hard work.

Vivek Vijay

This project has helped me understand the theories I have learnt so far in a practical way.

It has also given me some hands on experience and a kick start for my Senior Design

class. It has been a great pleasure to work with a group like this, with enthusiastic people

like Ben, Bader and Sean who were always there to help me and work on our project. I

would like to take this opportunity, to thank Professor Krogmeier, Srinivas, and Foo for

helping us and giving us all the encouragement in turning this project to a great success.

Introduction:

RFID, as everybody knows is one of the most innovative technologies in the wireless

sector. It is one of the solutions for many problems today in the wireless area. It replaces

bar codes, authorizes for access of protected areas, I-pass on toll ways, and provides body

temperature readings for physically challenged people.

The RFID team for Fall2004 proposes to build an RFID circuit that will be able to detect

temperature and transmit the information from the tag to the reader, eventually displaying

the actual reading on the reader side.

In order to meet the design requirements, the RFID team has identified the challenges

that need to be overcome.

1. How to transmit data from the tag to reader circuit?

2. How to interface a temperature sensor with the tag circuit?

3. How to implement the data display on the reader circuit?

Project Description:

I. Data Transmission Theory

As mentioned in the introduction, the goal in this data transmission project is to transmit

and display data on the reader circuit. As tag come into range to reader, the LC circuit

will create resonance. To enable data transmission, the RFID team is using amplitude

modulation, or AM, by using a switch to create short or open circuit on the tag end.

Figure 1: Left - AM Signal with switch operating at 1 Hz

Right – Zoom-in of the AM signal, displaying the carrier frequency at 1 MHz

II. Tag circuit switch

From measurement, the voltage of tag coil is 17 Vpp when it comes in range with reader

coil. As described in the progress report, MOSFET devices are considered as the ideal

switch device for the tag circuit. Since the tag voltage drops down to as low as -8.5 V, the

CMOS bilateral switch CD4066 is used with two 9 V size D alkaline battery to provide

over 17 Vpp. From measurement, when the input is not -9 V, the output will be open.

Thus, an inverting amplifier is placed before CD4066. Thus when the input is high, it will

be inverted and create a short.

Vin/R5 = - Vo/R4

Vin/-Vo = R5/R4 = 294/880

Vin = 5V, Vo = -9V

R 4

8 8 0

R 5

2 9 4

3

21

84

-

+

U 1 3 A

L M 3 9 3

CD4066BC

1314

7

21

Control A

VDD

VSS

Out/InIn/Out

V D D

V S S

t a g c a p

1

2

t a g c o il

R 61 k

V 1

Figure 2: Inverting amplifier and switch circuit

III. Shift Register Circuit

As desired to transmit 8 bits of I.D data and 8 bits of temperature data, the 74LS165

PISO shift registers are considered as the ideal data shifting method. The PISO consists

of 8 parallel input, 1 serial input, an active low load input, a clock input, and an output

QH. The astable operation of LM555 is used to generate clock signal at 1 Hz. Two HC393

up-counters are used to generate 24 clock cycles to provide clear. However, since 24 is

not in the power of 2, the output of up-counter is put into NOR gates, AND gates, then

inverter, to create active low for the load pin of shift registers. The data are loaded and

transmitted repetitively in every 32 clock cycles.

The start bits, end bits, and ID bits are connected to the parallel input of shift registers.

The temperature data is connected from the Binary-to-BCD PLD from the temperature

circuit. The serial input of the least significant bit (DS from the bottom shift register) is

connected to ground. So any other input data is considered as zero. The output QH is

connected to the serial input of each shift register. The output of the top shift register is

then outputted to the inverting amplifier.

Because the load pin happens at the falling edge of clock cycle, the most significant input

(pin 11) of the top PLD is not used as input.

Vin Vo

D S1 0

P 01 1

P 11 2

P 21 3

P 31 4

P 43

P 54

P 65

P 76

C P 12

C P 21 5

P L1

Q H9

Q H7

U 2

7 4 L S 1 6 5

D S1 0

P 01 1

P 11 2

P 21 3

P 31 4

P 43

P 54

P 65

P 76

C P 12

C P 21 5

P L1

Q H9

Q H7

U 3

7 4 L S 1 6 5

D S1 0

P 01 1

P 11 2

P 21 3

P 31 4

P 43

P 54

P 65

P 76

C P 12

C P 21 5

P L1

Q H9

Q H7

U 4

7 4 L S 1 6 5

Q A3

Q B4

Q C5

Q D6

C L K1

C L R2

U 5 A

5 4 H C 3 9 3

O U T3

R S T4

V C C8

C V5

TR G2 TH R6

D S C H G7

U 9

L M 5 5 5

Q A3

Q B4

Q C5

Q D6

C L K1

C L R2

U 1 0 A

5 4 H C 3 9 3

R 1

. 3 6 8 M

R 2. 4 6 9 M

C 20 . 0 1 u

C 11 u

V 15 V d c

V C C

V 1

2

31

U 1 1 A

7 4 0 2

5

64

U 1 1 B

7 4 0 2

1

23

U 1 2 A

7 4 0 8

4

56

U 1 2 B

7 4 0 8

9

1 08

U 1 2 C

7 4 0 8

V 29 V d c

V D D

V S S

V 39 V d c

Temperature Data

1 2U 1 4 A

7 4 0 4

End Bits (All High)

Start Bits (All High)

ID Bit

Figure 3: Shift Register Circuit

IV. Temperature Sensing Circuit

A simple and easy-to-integrate type of temperature sensor needs to be selected so the

measured data can be transmitted wirelessly and output on some 7-segment displays on

the reader circuit end. Voltage output and digital serial output sensors are the two major

types being considered for use. Digital sensor is the most ideal; however due to the

constraint of interfacing with shift registers that normally have parallel inputs, choosing

an analog sensor will be a more practical approach. For this particular project, the LM35

or the precision centigrade temperature sensor is adapted and its functionality has been

tested and proven. After properly connecting the sensor on the breadboard, an output

voltage linearly proportional to the Celsius temperature can be observed when human

thumb is firmly pressed against the chip.

Vout

An ADC0803 is also part of sensor integration because of the need for a digital output

ultimately. Found in EE402 instrument room, it appears to be common for labs and

projects and with less complication for implementation. New progress has been made to

validate the chip’s full scale adjustment, i.e. a 1.28 volt of reference voltage resulting in

eight ones of outputs with 0.01 volt per resolution. To ensure the proper functionality, the

CS input needs to be tied low and the conversion will start from 1 to 8 clock periods after

the WR input makes a low-to-high transition.

The issue of 8-bit binary to BCD conversion is resolved by building a truth table and

using a PLD 26v12 to implement (refer to the ABEL code in the end). One thing that is

worthwhile taking note of is that those chip pins which are not labeled as inputs are

required to be grounded or the PLD will otherwise malfunction.

Figure 4: Truth Table in ABEL format

Figure 5: PSPICE Schematics for integration of ADC0803 and PLD26v12

V. Reader Circuit

As soon as the data is received it goes into the original reader circuit and then the output

of the comparator goes into the shift register circuit. The provided clock is the output of

several components. The 555 timer runs at 10 Hz and the output of the timer goes into

the up pin of the counter. The counter counts from 0 to 15 however, to ensure correct

data transmission; we want to sample the data coming in at the middle of bit. Since data

is coming in at 1 Hz, the data is to best sampled when the counter reaches 5. The output

of the counter goes into the PLD. The ABEL code of the PLD is attached. This shows

that whenever the counter reaches 5, the PLD sends a pulse. This pulse acts as a clock for

my shift registers. The PLD sends another pulse to the counter whenever it reaches 10.

The edge detector circuit which is shown on the left is also used to improve clock

synchronization. It is the circuit which includes the four inverters and the AND gate.

The original design was supposed to have the data coming into the edge detector. The

edge detector resets the clock whenever it sees an edge. This is to further increase

synchronization. However, this did not work very well since whenever the edge detector

was connecting to the incoming data, the PLD for some reason did not provide the

required pulse. Therefore we simply connected the input to the edge detector to ground,

which is the same as not using the edge detector circuit at all.

ABEL CODE FOR THE CLOCK PLD:

Q3..Q0 pin;SCLOCK PIN istype ‘com’;CRESET PIN istype ‘com’;Edgedetector pin;

EQUATIONSSCLOCK = !Q3&Q2&!Q1&Q0CRESET = Q3&!Q2&Q1&!Q0

The shift registers then start shifting whenever it is provided with the clock.

The data is continuously being shifted by our SIPO shift registers. In order to display the

correct temperature with its corresponding ID, we made use of 4 ‘1’ Start bits and 3 ‘1’

Stop bits, which were fed into a 4-input AND gate. The result of this goes into our 2-

input AND gate, to give an output high only when all input bits were high. The output of

our AND gate was the enable of our PLD. The PLD works on the same bases of a PIPO

shift register, except for the fact that the input and the output pins are different. The Abel

code for the PLD is below.

ABEL Code to Replace the PIPO shift registers:

CLOCK pin 1; LOAD pin 2;I7..I0 pin;D7..D0 pin istype 'reg_d,buffer';EQUATIONS[D7..D0].d = LOAD & [I7..I0] # !LOAD & [D7..D0].q;[D7..D0].CLK = CLOCK;

Once the enable is high, the PLD latches the data currently present in the SIPO shift

register. This is then displayed on the common anode 7 segment displays using the LS47

7 segment decoders.

Figure 6: Complete Reader circuit

Timeline:

Week

1 August 23

2 August 30

3 September 6

4 September 13

5 September 20

6 September 27

7/8/9 October 4

October 11

October 18

10/11 October 25

November 1

12 November 8

13 November 15

14 November 22

15 November 29

16 December 4

Tasks

Team forming

Initial meeting and set goals

Analyze past design and theory

Design reconstruction and testing

Proposal review and continual research

Preliminary design

Tag modulation / Sensor Interfacing / Clock

synchronization / 7-Segment Display design

Mid-term Presentation

Design / Progress report

Design implementation

Design implementation

Design implementation

Thanksgiving Break

Testing / Final design review/ Outcome matrix

Integration / Final presentation

Semester Outcomes

The RFID team has successfully designed, built, tested, and implemented the temperature

sensing data transmission project. The tag circuit has effectively captured the temperature

data and converted the analog into digital data in BCD format, then transmitted to the

reader circuit by using shift registers and switch. The reader circuit has created a clock

and shifted the data into PLDs, and displayed it correctly. The clock synchronization part

on the reader side did not work as it was designed. The problem we believe is within

incorporating the edge detector into the rest of the circuit.

At the moment, this system is capable of detecting temperature ranges from zero to 40

degree Celsius while the tag circuit is completely inside the reader circuit. So far, the

overall system consists of nine breadboards, and the speed of data transmission is

operated at 30 seconds per cycle. There is leeway to improve the current project by

means of increasing the rate of transmission and changing the conductor value to better

RF receiving range. It is also achievable to broaden the temperature range by building a

more exhaustive truth table, and solder all components on PCB to provide mobility and

lower power consumption.

Transition Plans

The future RFID staff can always refer back to the documents and schematics created by

the previous semesters’ team for further design details. However since the goals for this

semester has already been achieved, future staff can utilize these available resources

based on what their project goals are.

Conclusion and Recommendation

This was definitely one of those projects that presented us with different challenges.

Throughout the semester the different parts of the project started to take their final shape

and eventually we integrated all the parts and achieved our goals of displaying

periodically the ID and temperature data.

One of the problems that we faced and hindered our progress was finding vacant space in

the labs to work on our project. We recommend arranging a certain lab for future teams

and have all the materials they need available to them.

References

[1] Bryan A. Chin. (2003). Radio Frequency Identification Sensors [WWW document]

URL http://www.audfs.eng.auburn.edu/docs/Nambisci2003.pdf

[2] P. Sorrells, Passive RFID basics, Microchip Technology Inc., 1998.

[3] MAX6613 Low-Voltage Analog Temperature Sensor. [WWW document]

URL: http://www.maxim-ic.com/quick_view2.cfm/qv_pk/3420.

[4] The RFID Handbook, Klaus Finkezeller, Wiley and Sons, Munich, 2000

[5] Microchip AN710 Antenna Circuit Design for RFID Applications Datasheet

[6] Asynchronous and Synchronous communications [WWW document]

URL: http://www.jbmelectronics.com/products/sync&a.htm

[7] Art of Electronics, Paul Horowitz, Cambridge England, 1989

Teaching Assistance

1. Professor James V. Krogmeier

2. Professor Robinson

3. Srinivas Vanjari, Ph D. student

4. Bingrui Foo, EE495M teaching assistant

5. Advait Behara, previous semester’s RFID team member