F12: Evil Watchdog

Abstract

A household dog.

The Evil Watchdog takes the responsibilities of a pet guarding a house. It will roam around a predefined environment, navigate around obstacles, and sound an alarm whenever foreign motion is detected. Although it cannot express love, it will not make a mess.

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

Hardware Implementation

Software Design

Software Implementation

Testing

Motor Controllers

The motor controllers were the first components to run through testing after the PWM driver was written. At first, the assumption was that a frequency of zero meant a full stop. That became untrue as the dog tried to run away at full speed even after the program shouted zero hertz. Once it was realized that higher frequency meant slower motion, the rear controller was successfully configured. The front motor was tested too. The main difficulty was in mapping out the voltage levels and voltage directions to see whether they corresponded to left, right, or center steering. Using LEDs helped figure out the mappings. An interesting point to note is that to return to center steering via GPIO, a change in steering direction must take place.

Distance Sensors

Motion Sensor

Alarm

Because the alarm worked with different voltages, it was tested on a voltage generator before being placed in the car. 3.3 volts was enough to supply an audible tone.

The Entire Dog

Once all the components were stitched and strapped onto the dog, the canine was released into the wild (the Engineering building hallways). It ran freely and occasionally bumped into walls. The distance sensor thresholds were modified to allow extra space between the dog and its nearest obstacles. At one point, steering froze for no apparent reason. A close examination revealed that super glue holding the distance sensor posts had dripped onto the front axle, preventing the dog from making turns.

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.

Check Opposites

When working with registers, double-check the code to see whether logic is written properly. Using IOSET and IOCLR, for instance, may seem easy and straightforward. However, they can easily become mixed up when a boolean checker is thrown into the mix. At one point during testing, the alarm rang when motion was sighted, and continued to ring forever. The suspect was an IOSET assignment that was instead supposed to be IOCLR. Once that was repaired, the dog ran happily again.

Distance Sensor Placement

Keep the side distance sensors pointing 45 degrees away from center sensor instead of perpendicular to it. Suggested by Preet, this allows the car to see more of its path ahead while maintaining some peripheral vision.

Motion Sensor Polling

The motion sensor is highly sensitive. It can detect slight movements in its environment. To avoid false alarms, modify the program to force the motion sensor to detect continuous movement before it decides to ring the alarm. By doing so, the system will ignore sudden movements assumed non-dangerous.

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.

F12: Evil Watchdog

Contents