F12: Evil Watchdog

Abstract

The Evil Watchdog takes the responsibilities of a pet guarding a house. It will roam around a predefined environment, avoid obstacles, and sound an alarm whenever foreign motion is detected.

Introduction

The objective of this project is to design a vehicle to imitate a guard dog. The following items will be incorporated to accomplish this goal :

• Motor driven chassis
• Vehicle will move in a random path detecting motion
• Vehicle will sound an alarm when motion is detected

Technology used

• Motion sensor
• Distance sensor

Team Members and Roles & Responsibilities

• Waymond Chen: Front motor control and distance sensor programming
• Hung Vuong: Distance and motion sensor programming
• Erik Montoya: Backside motor control and programming

Schedule

Starting	Ending	Planned Activities	Actual
Oct 26, 2012	Nov 1, 2012	Acquire parts Identify interfaces to be used Identify pin selections Review datasheets	Received distance sensors Received motion sensors
Nov 2, 2012	Nov 8, 2012	Build chassis Build motors and wheels Test motors and wheels	Prepared chassis and wheels Tested motors and steering
Nov 9, 2012	Nov 15, 2012	Write PWM driver Control rear wheels Program and test distance sensors	Created PWM driver Began controlling rear wheels Successfully tested distance sensors
Nov 16, 2012	Nov 22, 2012	Integrate motion sensor Test motion sensor Control/steer front wheels	Successfully tested motion sensor Integrated motion sensor Completed steering control
Nov 23, 2012	Nov 29, 2012	Integrate alarm system Unite all parts	Added piezo buzzer alarm United all parts
Nov 30, 2012	Dec 6, 2012	Testing and design final product Complete and revise project report
Dec 7, 2012	Dec 13, 2012	Finalize and deliver project
Dec 19, 2012	Dec 19, 2012	Demo project

Parts List and Costs

Item	Details	Source	Cost Ea.	Qty.	Total
Batteries	Duracell 1.5V Size AA	Costco	$1.33	x5	$6.65
Distance Sensors	SRF02 Ultrasonic Range Finder	Preet Kang	$25.00	x3	$75.00
LEDs	Blue and Green LEDs	HSC Electronics	$0.35	x2	$0.70
Microcontroller	ARM7 NXP LPC2148	Preet Kang	$60.00	x1	$60.00
Motion Sensor	PIR Motion Sensor SEN-08630	Preet Kang	$9.95	x1	$9.95
Motor Controllers	SJValley Engineering 5A Motor Controller	Dr. Özemek	$17.99	x2	$35.98
Piezo Buzzer	75dB 6VDC Piezo Buzzer	RadioShack	$3.89	x1	$3.89
RC Car	New Bright Land Rover Mud Slinger	Fry's Electronics	$15.34	x1	$15.34
Voltage Regulator	LM7805CV Voltage Regulator	HSC Electronics	$2.00	x1	$2.00

Design and Implementation

Hardware Design

Frame and Inner Placement

Original toy car prior to disassembly.

For convenience, a New Bright toy RC car was purchased and disassembled. The motors and wheels were already pre-mounted onto the chassis, allowing electronic parts to control the car. On the chassis, slots above the wheel wells were large enough to house motor controllers while the center of the chassis provided enough room to include a small breadboard and the microcontroller. All wires were shortened to the shortest length possible to reduce clutter.

Sensor Placement

The sensors, which guided car control, were strategically mounted in front and above the car. This increased visibility of the sensors. Three distance sensors were used to detect obstacles: a left-, a center-, and a right-side sensor was used to determine steering of the vehicle. A front-mounted sensor would seek motion as the car was stopped. Should motion be seen, the piezo buzzer sitting at the front of the car would promptly be sounded.

Power Supply

The battery box beneath the car provided additional convenience. It housed five 1.5-volt AA batteries that supplied up to 7.5 volts in series. This power supply provided enough power to run all of the components of this project. Whenever existing batteries began to run low on power, new batteries could be swapped into place easily. The following list describes the power requirements of each part used:

Part	Voltage Range	Source
Distance Sensors (Parallel)	+5V	Microcontroller Pin
LPC2148 Microcontroller	+7V to +20V	Battery Pack
Motion Sensors	+5V to +12V	Battery Pack
Motor Controllers	+7V to +30V	Battery Pack
Piezo Buzzer	+3V to +6V	Microcontroller Pin

Testing and Technical Challenges

Battery Life

By far, the battery pack is the most vulnerable component in keeping the Evil Watchdog alive. Only five 1.5-volt AA batteries power the entire system. Possible solutions to this problem are to either use batteries with longer lifespans or to use rechargeable batteries to avoid wasting single-use cells. During testing, a variable-voltage DC power supply, grabbing power from a wall outlet, was used to power the project. This saved battery power later needed for demoing.

Vehicle Weight

The original toy car was designed to carry a lightweight circuit board that received RF signals to control the motors. When the car is torn apart and new components are added for this project, the amount of weight placed on the wheels rapidly increases. Additional weight requires extra torque from the wheels to move the carried load, which can drain the batteries much more quickly. The best way to alleviate this problem is to eliminate excess weight and to select the lightest available parts to be placed on the vehicle.

References

Thanks To...

• Dr. Haluk Özemek
• Preet Kang, TA

Appendix

• Project Code: (FIXME)
• Project Video: (FIXME)