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INTRODUCTION. Nearly all modern cars are equipped with a Remote Keyless Entry system. Such systems allow the user to remotely:. Lock/Unlock doors Open trunks Open Doors Arm Alarms Set off Panic Alarms.

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INTRODUCTION

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Introduction

INTRODUCTION

Nearly all modern cars are equipped with a Remote Keyless Entry system. Such systems allow the user to remotely:

  • Lock/Unlock doors

  • Open trunks

  • Open Doors

  • Arm Alarms

  • Set off Panic Alarms

Other uses for the system have evolved, such as using the horn beep from the car to help locate it in a parking lot

RKE REPEATER

RIT SEINOR DESIGN ‘04


Objective

OBJECTIVE

The nature of RKE implementation often leads to limited range. There are several advantages to extending the range of the system. Among these is locating a lost car in a parking lot.

Normal Range: 15 to 100 ft.

RKE REPEATER

RIT SEINOR DESIGN ‘04


Objective1

OBJECTIVE

The objective of this design will be to extend the range of an existing RKE system to greater than 200 ft. by placing a high performance repeater in the automobile

RF

Repeater

Extended Range: 200+ ft.

RKE REPEATER

RIT SEINOR DESIGN ‘04


Project scope

PROJECT SCOPE

Customer Specifications

  • The repeater must be a stand alone device.

  • The repeater must be easy to install, not attaching to anything in the vehicle.

  • The repeater should be able to be sold for between $20 and $50.

  • The repeater should be able to interact with all or most existing RKE systems.

RKE REPEATER

RIT SEINOR DESIGN ‘04


Project scope1

PROJECT SCOPE

Final Design Specifications:

  • A repeater for RKE systems will be designed and constructed to extend the range of the preexisting systems.

  • It will be a stand alone device independent of the vehicle and the existing RKE system.

  • It will have its own power supply.

  • It will be small and portable.

  • It will be able to work with most existing RKE systems.

RKE REPEATER

RIT SEINOR DESIGN ‘04


Project scope2

PROJECT SCOPE

Design Constraints

  • Frequency Shift Keying (FSK) key fobs cannot be used

  • Separate units for 315 MHz and 433 MHz operation

  • Use of ASK modulation

  • Power supply is limited to batteries

  • Antenna must be omni-directional

RKE REPEATER

RIT SEINOR DESIGN ‘04


Rke background

RKE BACKGROUND

The systems commonly operate on an unlicensed portion of the spectrum intended for intermittent transmission of digital control signals.

Some common RKE systems specifications:

  • Frequency: 315 or 433 MHz

  • Data Rate: < 5000 bps

  • Modulation: ASK

  • Range: 15 to 100 ft

  • Output Power: 1 mW

RKE REPEATER

RIT SEINOR DESIGN ‘04


Rke background1

RKE BACKGROUND

b0| b1 | . . . | bn | bn+1 | bn+2 |. . . . . . . | b60

Intro and control code

“Hopping” Security Code

In order to ensure the security of the transmission, a pseudo-random “hopping code” is combined with a control code.

Key Fob Sends:

Code 0

Car Receives Signal and Compares:

Code 1

Execute Command

Code 2

Received Code

Code 255

*Note: Encoding of actual systems varies. For security reasons, exact specifications of many systems are not available. This is meant as a representation of such systems.

RKE REPEATER

RIT SEINOR DESIGN ‘04


Repeater background

REPEATER BACKGROUND

Repeating is not a new technology. Most existing repeater systems operate as follows:

Normal Repeater Design:

  • Receives signal at some frequency ƒ

  • Shifts input signal by some frequency ƒ1

  • Retransmits shifted signal ƒ+ƒ1

  • Normally receives and retransmits on the same antenna.

    • The receiver and transmitter are isolated due to frequency shift

  • Many different repeater designs exist using this method and are used in communications.

    • i.e. Cellular and radio networks

RKE REPEATER

RIT SEINOR DESIGN ‘04


System overview

SYSTEM OVERVIEW

Antenna

Transmitter/Receiver Switch

Receiver

Transmitter

Controller

Repeater Circuitry

  • Division of Labor:

    • Naanzem – AntennaSurat – Receiver, Transmitter, and T/R SwitchBrian - Receiver, Transmitter, and T/R SwitchBill – Controller, Detection

RKE REPEATER

RIT SEINOR DESIGN ‘04


Design antenna

DESIGN: ANTENNA

  • The design of the antenna is limited by the wavelength, ~1m, and the fact that it has to be omni-directional. Possible antenna designs are:

RKE REPEATER

RIT SEINOR DESIGN ‘04


Feasibility antenna

FEASIBILITY: ANTENNA

RKE REPEATER

RIT SEINOR DESIGN ‘04


Antenna design

ANTENNA DESIGN

The antenna used is a quarter wavelength dipole.

RKE REPEATER

RIT SEINOR DESIGN ‘04


Impedance matching

Impedance Matching

The impedance of the antenna does not match the input impedance of T/R switch. A miss-match in impedance creates a loss in the signal. Therefore, a match was designed and is shown:

RKE REPEATER

RIT SEINOR DESIGN ‘04


Design receiver

DESIGN: RECEIVER

Filter # 1

Filter # 2

1st IF Stages

Detector

Injection Filter

1st IF Amplifier

RF Amplifier

1st Local Oscillator

The basic receiver design is:

Requirements:

  • Low power consumption

  • Low cost

  • High Gain

    There are two design options:

  • Build from discrete components

  • Use a Receiver Chip that has been designed for RKE systems.

RKE REPEATER

RIT SEINOR DESIGN ‘04


Receiver design

RECEIVER DESIGN

The rfRXD0420, produced by Microchip, was chosen as the receiver chip because it best suited the specifications for the receiver. This receiver has the following properties:

  • Frequency Range:300-450 MHz

  • Modulation Types: ASK/FSK

  • Price: $2.79

  • Current Draw: 8.2 mA and <100 nA standby

  • Bit Rate: 80 kbps

COMPONENT: Microchip rfRXD0420

RKE REPEATER

RIT SEINOR DESIGN ‘04


Receiver design1

RECEIVER DESIGN

The main receiver functions are already implemented. The filter must still be designed.

RKE REPEATER

RIT SEINOR DESIGN ‘04


Rx tx switch design

Rx/Tx Switch Design

There is only a single antenna for this system. Therefore, a switch is needed to keep the receiver and transmitter isolated. The switch used is ADG919, manufactured by Analog Devices.

  • Bandwidth: 4GHz

  • Isolation: 43dB

  • Price: $1.07

  • Current Draw:<1uA

RKE REPEATER

RIT SEINOR DESIGN ‘04


Rx tx switch design cont

Rx/Tx Switch Design (cont.)

The Rx/Tx Switch Circuit is:

RKE REPEATER

RIT SEINOR DESIGN ‘04


Design concepts transmitter

Design Concepts: Transmitter

Directional coupler

Low Pass filter

Diagnostics

Forward

Reverse

Modulation Input

Power Controller

The basic transmitter design is:

Requirements

  • Low power consumption

  • Low cost

    There are two design options:

  • Build from discrete components

  • Use a Transmitter Chip that has been designed for RKE systems.

RKE REPEATER

RIT SEINOR DESIGN ‘04


Transmitter design

TRANSMITTER DESIGN

The MAX1472 Chip is produced by MAXIM. This transmitter has the following properties:

  • Frequency Range: 300-450 MHz

  • Modulation: ASK

  • Amplification: up to +10dBm

  • Current Draw: 5.3 mA

  • Price: $3.74

RKE REPEATER

RIT SEINOR DESIGN ‘04


Transmitter design cont

Transmitter Design (cont.)

The Transmitter Output Circuit is shown:

RKE REPEATER

RIT SEINOR DESIGN ‘04


Design concepts filters

Design Concepts: Filters

Passive Filters

Active Filters

SAW Filters

Noise is an important consideration in this system. Therefore, there are different filters needed in the system. The different filters are:

  • Preselector

  • IF Filter

  • Transmitter Output Filter

RKE REPEATER

RIT SEINOR DESIGN ‘04

http://global.kyocera.com/prdct/electro/new/sf16/images/sf16_01.jpg


Feasibility filters

Feasibility: Filters

Passive Filters

Active Filters

SAW Filters

The most important consideration for the filter design is the power consumption of the filter.

Use for:

Preselector

Use for:

IF filter

Tx Filter

http://global.kyocera.com/prdct/electro/new/sf16/images/sf16_01.jpg

RKE REPEATER

RIT SEINOR DESIGN ‘04


Preselector design

Preselector Design

The Preselector used is a SAW filter.

  • Product number: 162988

  • Manufacturer: COM DEV Saw Products

  • Center Frequency: 315 MHz

  • Bandwidth: 430 kHz

  • Price: $1.67

RKE REPEATER

RIT SEINOR DESIGN ‘04


Low pass filter designs

Low Pass Filter Designs

The designs for the Low Pass filters are:

RKE REPEATER

RIT SEINOR DESIGN ‘04


Design concepts repeater

Design Concepts: Repeater

Sample the Signal

  • The signal is sampled using an A/D converted and then stored in memory.

    Demodulate Microcontroller

  • The signal is demodulated using an envelop detector and then delayed using memory. This process uses a microcontroller.

    Demodulate DSP

  • The signal is demodulated and then processed using a DSP.

    Simultaneous Retransmission

  • The signal is received on one antenna and then retransmitted using a separate antenna.

RKE REPEATER

RIT SEINOR DESIGN ‘04


Control system design

Control System Design

A Microchip PIC16F87 was selected as the microcontroller.

  • Features:

  • High speed, low power operation.

  • Sufficient I/O Capabilities

  • Low cost

  • Simple but adequate instruction set.

RKE REPEATER

RIT SEINOR DESIGN ‘04


Microcontroller design

Microcontroller Design

  • Set inputs, outputs and interrupts

  • RX Enabled

  • TX Disabled

Set System on Startup

Listen for Signal

Receive Signal

Transmit Signal

RKE REPEATER

RIT SEINOR DESIGN ‘04


Microcontroller design1

Microcontroller Design

Wait for interrupt on signal change

Set System on Startup

Listen for Signal

Receive Signal

Transmit Signal

RKE REPEATER

RIT SEINOR DESIGN ‘04


Microcontroller design2

Microcontroller Design

Record received data until end

Set System on Startup

Listen for Signal

Receive Signal

Transmit Signal

RKE REPEATER

RIT SEINOR DESIGN ‘04


Microcontroller design3

Microcontroller Design

Send Data

Set System on Startup

Listen for Signal

Receive Signal

Transmit Signal

RKE REPEATER

RIT SEINOR DESIGN ‘04


Receive schematic

Receive Schematic

RKE REPEATER

RIT SEINOR DESIGN ‘04


Transmit schematic

Transmit Schematic

RKE REPEATER

RIT SEINOR DESIGN ‘04


Full schematic

Full Schematic

RKE REPEATER

RIT SEINOR DESIGN ‘04


Conclusion

Conclusion

  • The object for this project is to design an RF repeater that will extend the range of most vehicle’s existing RKE systems.

  • The repeater design demodulates the input signal and then stores the signal in a microcontroller. The signal is then demodulated and transmitted.

  • The total cost of the design is estimated to $23.31.

RKE REPEATER

RIT SEINOR DESIGN ‘04


Acknowledgements

Acknowledgements

  • Dr. Phillips

  • Dr. Venkataraman

  • Professor Perlman

  • Professor Slack

  • Paul Jacobs

  • Jan Van Nekeerk

    1.http://global.kyocera.com/prdct/electro/new/sf16/images/sf16_01.jpg

RKE REPEATER

RIT SEINOR DESIGN ‘04


Question answer

Question & Answer

RKE REPEATER

RIT SEINOR DESIGN ‘04


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