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

2. Motivation

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

4. 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

5. 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

6. Final Product Key Holders User Interface Activator Toggle
Key Connector

7. System Overview

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

9. 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

10. RFID Reader Parallax RFID Read/Write Module Identifies tag
< 2 seconds
Through housing
Up to 3.5 inches away

11. RFID Tags To be placed near the locks or keys 125 kHz signal
Data can be read/written into its internal memory

12. 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

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

14. 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

15. Controller Module Arduino IDE code Microcontroller Unit
ATMega328 for processing and sending signal to key holder circuits
Arduino IDE code

16. Controller

17. State Machine: Start

18. State Machine: New Key

19. State Machine: Key Search

20. 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

21. 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

22. Power Module DC/DC converter 5V to RFID and MCU Charging Circuit2k
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

23. 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

24. 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

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

26. 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

27. 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

28. 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

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

30. Questions?