midway design review

Department of Electrical and Computer Engineering

Team BeepachUNovember 26, 2013

Midway Design Review

Department of Electrical and Computer Engineering

Team 7 Members

Eric WagnerEE

David ZeifmanCSE

Mark WagnerEE

Quanquan HanEE

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This Presentation: Overview

Review: What is BeepachU?

Block Diagram: Old and New

Demos: TX/RX and working Audio

CDR deliverables, Team Responsibilites, and Schedule

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Review

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Review: What is BeepachU?

Problem: Lost items Solution: Cheap tracking tag that makes sounds to lead

you to your item Key Fob transmits to tag tag makes sound for user

Where’s my Wallet?

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Review: BeepachU Specifications

Range: 100m (outdoor line of sight) Battery life: 6 months for both Keyfob and Tag Weight: Keyfob < .5 lb, Tag < .5 Ib Response time: under 2 seconds Size:

• Keyfob < 4 square inches• Tag < 3 square inches

Robust• Tag will not be set off by interference signal

Cheap: Each unit < $30 when mass produced

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Block Diagram

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Previous Block Diagram

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Redesigned Block Diagram

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Block Diagram: ANT SoC Block

Contains the nRF51422 “ultra low power” ANT SoC

ANT, like bluetooth, is a network protocol

ANT is pre-implemented in software on the chip

Programmed in C

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Block Diagram: Network Diagram (using ANT protocol)

ANT Protocol uses time-division multiplexing to separate channels

Master and Slave devices are preset only to connect with eachother

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Block Diagram: Speaker System

LM 386 audio amplifier- $0.34 CDM-10008 8 Ohm speaker- $0.79 2.9mm height, 10mm diameter

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Block Diagram: User Interface

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Block Diagram: Power Supply 3V CR-2032/VP Energizer coin cell battery 225mAh lifespan 0.79” diameter x 0.13” height $0.40 per battery One battery per keyfob, two per tag

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Block Diagram: Antenna + PCB

Same PCB used for keyfob and tag (reduces cost)

PCB = 1.2 x 1.5 inches

“Inverted F” antenna integrated into PCB• Isotropic, often used in cell

phones• Can be tuned manually by

scraping copper off its end

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Demonstrations

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Review of Proposed MDR Deliverables

Demonstration of working TX/RX• TX and RX recognize each other and work at close distance• TX and RX hardware not necessarily contained in small

package (may be on a breadboard or Development Kit Module)• Not yet battery powered

Working speakers driven by TX/RX hardware• Small audio system will be operational• Same transceiver SoC that drives TX/RX must be able to drive

audio system.• Not yet battery Powered

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Demonstration

Transmit/Receive Demo Audio Demo

Enjoy

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CDR Deliverables, Team

Responsibilities, and Schedule

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Proposed CDR Deliverables

Fully functional system• Doesn’t necessarily meet specs, but works• Powered by battery• Implemented on custom PCB not development board• Hot cold feature implemented• Beep will work and will be audible

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Individual Responsibilities

Dave ZeifmanProduce finalized & power efficient BeepachU TX/RX code

Eric WagnerOrder and Test PCB module with integrated AntennaTune Antenna for optimal performance

Mark WagnerProduce finalized audio driving code

Quanquan HanProduce packaging + integrate packaging with PCB

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Schedule

Department of Electrical and Computer Engineering

Questions?

Thank You

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Power Specifications (with 3.3V source) Keyfob (on)

• Sleep mode = 8.25uW (or 2.5uA)• Transmitting as master device = 8.58mW (or 2.6mA)• Transmitting + LED on = 16.8mW (or 5.1mA)• Battery indication LED = 8.25mW (2.5mA)

RX (always on)• RX sleep/search mode (10% duty cycle) = 262.2mW (or

79.5uA)• Paired as slave device = 8.58mW (or 2.6mA)• Paired as slave + beep and blink= 640.2mW (or 194mA)

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Power Usage Estimations Keyfob (TX) is on for about 2 minutes per use

• Transmitting + LED on (for Hot/cold): 120s

• Battery indication LED: 120s

• Total = 912 mAs = 0.2533 mAh (888 uses) Tag (RX) is used for 2 minutes per use

• Hot/Cold active (connected) : 115s

• Beep & LEDs active: 5s

• Total = 1269mAs = 0.3525mAh (297 uses)

Tag (RX) is on sleep/search mode for the rest of the time

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Preliminary Cost Analysis

“Each unit < $30 when mass produced”

Part (quantity) Quantity (keyfob)

Quantity(Tag)

Cost

Chip Cap/Ind/Resistors 17 17 $0.01 x 17 = $0.17

nRF51422 (ANT SoC) 1 1 $3.13

NX2520SA 16 MHz crystal 1 1 $0.51

LM386 Audio Amp 1 1 $0.34

LED 2 2 $0.50 x 2 = $1.00

Speaker 0 1 $0.79

Battery 1 2 $0.40 x 2 = $0.80

PCB 1 1 $5.00

Total: $10.95 $11.74 $22.69

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Multiple Tags for a Single Keyfob?

ANT allows for “star networks” with one master (keyfob) and multiple slaves (tags)

Tags must be paired with masters during initial programming

multiple tags will have to be bought alongside the keyfob

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ANT Network Security

Can use Single Channel Encryption• 128-bit AES-CTR (symmetric algorithm –

single shared key)• Supports multiple slaves per master on single

channel, but only one channel per master

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Responsibilities : Dave Zeifman

Keyfob Programming• Keyfob must initiate connection with tag when hot/cold is active• Must display RSSI in accurate manner using LED• Must be power efficient

Tag Programming• Tag must constantly search for Keyfob• Tag must know when to connect and when to beep• Must be power efficient

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Responsibilities : Mark Wagner

Sound Driver • Store “Beep” sound bite in chip• Write audio driving code for receiver• Generate pleasant and audible beeping sound• Acceptable power consumption

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Responsibilities : Eric Wagner

PCB• Must be able to support all buttons/LEDs/speakers on UI• Must fit size specifications• Must be cheap enough to produce on BeepachU budget

Antenna • Must be nearly isotropic in tag, can be directional in keyfob• Must have high enough efficiency to meet range requirements• Must be tunable

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Responsibilities: Quanquan Han

UI/Packaging• Must fabricate packaging• Fabrication should be within BeepachU budget• Buttons, LEDs and Speakers must be integrated into package• Package must not muffle tag beeps• Package must not interfere with antenna