The Enforcer

• Laura Celentano

• Glenn Ramsey

• Michael Szalkowski

SPEEDLIMIT

65RF

Overview

• Autonomous vehicle speed control system

• RFID speed limit signs

• RFID reader detects signs

• Car automatically changes speed to reflect limit

System Interface

• 2 Switches and 2 Lights– Power– Operation

• 2 7-Segment Displays– Speed (ft/s)– X.X format

PowerOff

On

Off

On

Operation

Radio Frequency Identification (RFID)

• Method of identifying unique items using radio waves

- Identification, location, price, color, etc.

- Found on products (Wal-Mart), E-ZPass, etc.

EM4102 Thin Card RF Transmitter

Parallel Read Range = ~4.75'' Perpendicular Read Range = ~0.5''

~4.75''

VehicleDirection

InductiveCoil

3.75''

Magnetic Field (Signal Range)

~0.5''

~0.5''

Radio Frequency Identification (RFID)

• RFID Subsystem Consists of a Reader and a Tag– Reader: one or more

antennae used to interrogate a tag

– Tag: relays pertinent information back to reader

– Two types: Passive vs. Active

RFID Testing Results

• Analytic Components– Vehicle Speed Limitations

• How fast can we pass by a tag and make a successful communication?

– Track Following Requirements• How close must we be to the tag to make a

successful communication?

smsftin

tt

RangeSignalV

transferreader

2195.603057.030/1

75.4_max

2in

RFID Detection

• Underpass Design– More robust method of detecting RFID Tags– Reader equipped to the top of the vehicle ensures that it will

always be within the acceptable read range– Eases burden on track detection algorithm; loosens accuracy

requirement for staying precisely on the track

RFIDTag

RFID Tag

Track Following

• IR Sensors

• Reflective Track

Reflective Surface

IR IRIR

Sensor Specs

• Fairchild QRB1134

• Rise and fall times 8 us

• Allows for over 500 samples per meter at vehicle’s possible max speed

• Comparator provides TTL output

Processing

• HCS12 timer fires at regular intervals and captures the sensor input

• Algorithm interprets sensor input

• For safety purposes, operation is suspended if the track is lost (“unknown state”)

Go straight.

Suspend operation.

Turn right hard.Turn left hard.

Turn right slightly.Turn left slightly.

Right sensorloses track

Right sensorregains track

Middle sensorloses track

Middle sensorregains track

Left sensorregains track

Left sensorloses track

Middle sensorloses track

Middle sensorregains track

Right sensorloses track

Left sensorloses track

Start

Power System

• Power System– 9.6V Rechargeable

Battery• DC Motor

– 5V Regulator• Servo Motor• Microcontroller• Support Hardware• 1 A

– Need 865 mA

Direction and Speed Control

• Direction Control– Servo Motor– 16-bit PWM

• Speed Control– DC Motor– L6203

• DMOS Full Bridge Driver

– Capable of multi-speed forward and reverse operation

– 2 16-bit PWMs

Speed Detection

• Shaft Encoder– Notched Wheel

• OPB930W– Slotted Optical Switch– TTL Output– 5 us Propagation Delay– Connected to a Timer Input Capture

Testing Strategy

• Individual Component Testing– RFID Communication

• Define 3 distinct speeds, associate unique ID#• Construct underpass of appropriate dimensions

– Track Following Algorithm• Proper sensor operation verification• Verify vehicle can make turns following track

– Vehicle Speed Calculation & Control• Verify direction control• Verify speedometer• Verify speed control unit for the 6 speed transitions

• Full System Integration Testing

Possible Problems

• Missed RFID tag communication

• Possible loss of track

• Different speeds require different turning angles

• Mounting the shaft encoders

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