UCLA IEEENATCAR 2004 SUMMER

CLASS

Magnetic Sensors&

Power Regulation

Introduction

Wilson Chen Internal Vice President IEEE NATCAR member 03

Sensor Circuit P.I.D Algorithm Power Management

Magnetic Field and Coil What does a 75kHz, 100mA rms

AC current mean? Magnetic Field around a wire

(1/r2) Brief review of inductor

V = L (di / dt)

Different Orientation of Inductor

Horizontally above the wire

Advantage Provide continuous

band of reading Disadvantage

Relatively short range Can sacrifice reading

amplitude for range

Cont. Vertically above the wire Advantage

Very long range of detection

Disadvantage 0 reading when on

directly on top of the wire Must program with

caution

Comparison between Optical Sensor and Magnetic Sensor

Magnetic sensor provides a relatively long range of analog reading while optical sensor only provides discrete reading of 1 or 0.

Magnetic sensor is very sensitive to noise. The signal obtained thus is not often clean; Optical sensor outputs a clean signal of 1s and 0s.

Building a Magnetic Sensor Circuit

Different Stages

LC Tank Filter Amplifier

RectifierProcessor

LC Tank

+

-

C 4

1 7 0 p

L 1

2 2 m H

1

2

Vout

LC tank, which is an energy storage device, is our sensing unit.

Resonance Frequency ωr = √(1/(LC))

Theoretical value vs. practical value

Filters Review of bandpass filters

Center Frequency, Cut-off Frequencies Minimize bandwidth

Types of bandpass filters RC lowpass and RC high pass Active bandpass filter

Filters

+

C 1

1 7 0 p

R 1

3 k

--

I N

VoutVin

O U T1

0

O U T2C 3

1 7 0 p

R 3

1 0 0 k

+

RC lowpass cascaded with RC highpass filter

Designing a Filter It’s very crucial to set the center

frequency at 75kHz Make sure gain is closed to 1 Determine cut-off frequencies

Low end: 60Hz (surrounding noise) High end: 400kHz (AM radio)

Design Techniques Calculate theoretical values Use PSpice to run simulations with different

values. Use the simulation results.

Filter Yes, after all these

talks, filter is only an optional component in this particular sensor circuit. =(

Frequency

1.0KHz 3.0KHz 10KHz 30KHz 100KHz 300KHz 1.0MHz 3.0MHz 10MHzV(OUT1) / V(IN) V(OUT2) / V(OUT1)

0

0.5

1.0

Frequency

1.0KHz 3.0KHz 10KHz 30KHz 100KHz 300KHz 1.0MHz 3.0MHz 10MHzV(OUT2) / V(IN)

0

0.5

1.0

Amplifier Circuit Amplifier circuit is the most important

part of our sensor circuit design. What does an amplifier do and how

does it work? Choosing an amplifier circuit

Simple and straight forward Can precisely adjust the gain easily Don’t use any inverting amplifier

Building an Amplifier Circuit Choose the right type of OPAMP chip

Use Qua-OPAMP Voltage operational range (+/- 5V) Frequency operational range Notice that you will only have VCC+

Use potentiometer to set amplifier gain Make sure your gain is not large enough

to saturate the OPAMP when the sensor is directly on top of the wire

Amplifier Cont.

Don’t use this! This is an inverting amplifier. 0

Vin

V 31 0 V d c

-

+

U 1 A

M C 3 3 1 7 4 / S O

3

21

411

R 1

5 0 0 k

0

Vout

V 2-1 0 V d c

R 2

1 0 0 k

Rectifier Review of diode What is a rectifier

Full wave rectifier Half wave rectifier

C3

100n

OUT

D1

D1N4148

R5

100k

0

Building a rectifier Realize there is a 0.7v drop

across the diode Choose the RC value carefully

RC should be much greater than 1/f

However, if RC is too big, the response of the sensor circuit output would be slow.

Complete Sensor Circuit

C3

100n

C2

170p

FilterR3

3k

IN

R1

500k

U2

OPAMP

+

-

OUTC1

170pOUT

R2

50k

D1

D1N4148

OPAMPV1

FREQ = 75kVAMPL = 1vVOFF = 0

R5

100k

0

R4

100k

0

Input and Output

Time

0s 10us 20us 30us 40us 50us 60us 70us 80us 90us 100usV(OUT) V(IN)

-2.0V

0V

2.0V

4.0V

6.0V

Sensor Systems The more sensors you have, the more

information we can obtain about the current position of your car. Prepare for at least 5 sensor circuits

Design the range of your sensors It’s not necessary to be good to have too

long of a range Again, lifting sensors will give u a longer

range

How do we orient sensors The most basic

configuration Left, right and center Self correction P.I.D. ready Sufficient enough to handle

most of the track Advance configuration

More side sensors to handle special cases

Front sensors to detect curve

Dealing with sensors Sensor reading plot is EXTREMELY

important!!! sensor readi ng

-1-0. 5

00. 5

11. 5

22. 5

33. 5

4

-100 -80 -60 -40 -20 0 20 40 60 80 100

posi t i on

volt

age Center

Lef tRi ghtSeri es4

Dealing with sensors Discover a lot of small, but

every important behaviors of your sensors

Reading is a exponential function Manipulate all the readings and

generate a linear output

Dealing with noises Noises from power source

Filters Ground noises

Filters? Avoid ground loops as much as

possible PCB Ground Strap

Other Tips Use twisted wire for sensors Stabilize sensors as much as

possible Tape? Glue?

Use terminal blocks only for power connections; For sensors, use connection pins.

Power Regulation Why do we need power regulation? Device the needs to be regulated

Servo Sensor Circuit Motor??

Types of regulator Switching Regulator (bad guy for us!!)

Possibly reduce power consumption Linear Voltage Regulator

Low drop-out

The End