Key Master Group 14 Petar Barac, Amanda Beck, & Leslie Cheng ECE 445 Senior Design April 27, 2017

Motivation

Actual Motivation Tim has too many keys, way too many keys

Introduction The Key Master is an easy-to-use key identification system for matching keys to locks Utilizes RFID technology with tags placed near locks RFID reader embedded in key ring will read nearby tag when activated by user LED to matching key will blink Concept Drawing

Features Modular design Add new keys Key ring bus holds 6+ keys Helpful LED user interface Lasts over 8 hours or a minimum of 100 tag reads Recharging capability for daily use

Final Product Key Holders User Interface Activator Toggle Key Connector

System Overview

System Overview Recharging Circuit New Key Bus Key Ring Bus RFID Reader DC/DC Converter USB Connect Microcontroller Socket Main PCB

RFID Module RFID Read/Write Module and tags Wrote unique addresses to each tag based on Key Holder Circuit 1-Wire IC for unique global identification

RFID Reader Parallax RFID Read/Write Module Identifies tag < 2 seconds Through housing Up to 3.5 inches away https://www.parallax.com/product/28440

RFID Tags To be placed near the locks or keys 125 kHz signal Data can be read/written into its internal memory     http://www.robottwinkee.com/product_p/32399.htm

Key Holder PCB less than 1 in2 Physical contacts from ground and bus Necessary Requirements LED must be visible in well lit room from a yard away Addresses the right key all the time Bus Contact Points Key Connector 1 Wire Circuit Battery

Key Holder Circuit DS2413 Chip 1-Wire Dual Channel Addressable Switch Unique address on each chip

Key Holder Modifications Original Design Change/Fix Copper finger connects along outer side of bus Manual pressure to inner surface of bus Holder contains circuit Tight fit affected contacts Parasitic power to LED Additional power source required CR1620 batteries

Controller Module Arduino IDE code Microcontroller Unit ATMega328 for processing and sending signal to key holder circuits Arduino IDE code https://www.microchip.com/_images/ics/medium-ATmega328-SPDIP-28.png

Controller

State Machine: Start

State Machine: New Key

State Machine: Key Search

Controller Modifications Original Design Change/Fix ATMega8P ATMega328 for easier programming AVR programmer for code updates Loaded via Arduino Uno board PCB connected Perf board for better pin access

Power Module Recharging Circuit Power Source 9 V Lithium Ion Polymer Battery with a step down DC/DC converter Recharging Circuit USB fed boost converter with linear regulator feeds battery http://www.batterymart.com/p-r-li9720-9volt-lithium-polymer-battery.html

Power Module DC/DC converter 5V to RFID and MCU Charging Circuit 2k Battery IC solutions chosen to save on space – smaller inductors because faster oscillators than available form MCU (156 kHz versus 32 kHz) is the difference between a 1.15 mH inductor at .25 in^3 versus a 100 uH inductor at a quarter of the size Linear regulator provided over voltage, over current, and thermal regulation Selection of LM317 regulator based on battery safety suggestions, but a (boost) step up converter was needed from the DC of the USB input USB was because the AVR was already incorporated. DC/DC converter allows for undervoltage protection 5V to RFID and MCU Charging Circuit

Power Source Capacity Requirements Must also provide minimum of 5 V 9 V worked best Mode RFID [mA] MCU [mA] Time [hours] [mAh] Active 200 3.6 0.8 162.9 Standby 20 1 7.2 151.2 Total 8 314.1

Charging Circuit Battery ranges from 7.5 V to 8.4 V Design to charge < 12 hours Consists of converter and linear regulator Current flow slows as battery approaches maximum voltage Shuts down if maximum voltage is overshot Slows current flow as battery approaches minimum voltage Will shut down if maximum voltage is overshot Linear regulator has overcurrent limiter

Power Modifications Original Design Change/Fix Step down converter feeds to modules Parallel linear regulators used after converter damaged

SWOT Analysis Strengths: Modular Simple charging Quick key identification Weakness: Bulky Limited key capacity Key mobility Threats: FOB/Card access systems Opportunities: Facilities Management Residential Managers

Conclusion Main functionalities of identifying keys successful Modularity of design for adding key worked Charging circuit provided sufficient power and control to safely recharge battery

Future Work Key ring bus contact redesign Third bus to key holders Remove key holder batteries Housing sizing Further compact elements Move charger out Smaller RFID module Custom build

Credits and Thanks Project TA: Jacob Bryan Power TA: Jackson Lenz ECE Machine Shop Crew Scott McDonald Gregg Bennett

Questions?