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RF Football Sensor

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					RF Football Sensor
Proposal
ECE 445, Spring 2005

Kavin Arumugham And Arjun Majumdar

Introduction As most football fans can attest to, the delay as well as uncertainty involved with instant replay and referee subjectivity can be quite frustrating in the NFL. To help alleviate this problem, we would like to prototype a system that would minimize as much as possible any guess work or instant replay involved in determining ball placement. This wireless system is also intended to supply accurate first-down data by displaying the flight path of the football on a display unit available to the referees. This is a project that excites us since we both follow football and our respective teams every year and have the opportunity to apply our engineering skills to an area that isn’t traditionally thought of as a technology sector.

Objective Our goal is to produce a chip (<1”x1”) to be placed in a football that would communicate with a base station on the sidelines of the football field transmitting position information that could then be displayed on a computer interface. We would like to model our design similar to that of the Bird Accelerometer II project done in Fall 2004. The function of the project is to display the movement of a football clearly on a computer screen. Benefits  Measure football position anywhere on the field, and follow its flight path  Determine whether ball has crossed goal line for touchdown  Determine whether offense has achieved a first down  Verify whether pass was “caught” or “trapped”  Allow measurement of throws (velocity) Features  Temperature Operating Range (-30° C - 85°C)  Visual Display of Ball Flight  Ability to Recall Ball Movements for Duration of Game  Weatherproof Seal

Design: General Block Diagram

Receiver

Data Acquisition and Transmission

Analysis/Storage PC

Data Acquisition and Transmission Design
I. Block Diagram

Lightweight Battery

Dual Axis Accelerometer (XY)

Select

Dual Axis Accelerometer (YZ) Dual Axis Accelerometer (XZ)

8x1 MUX
Data

PIC LINX

II. Description Dual Axis Accelerometers These accelerometers will need to be capable of detecting the acceleration of the football. They will probably be ADXL202 +/- 2g chips (or possibly the ADXL210), because of there considerably low cost, as compared to three axis chips. The output of the accelerometers is PWM, which will go to six inputs of the mux. Three accelerometers will be used to make two measurements on each axis, which can then be averaged reducing error. 8 x 1 MUX The MUX will be used to select one axis of a single accelerometer at a time. This data will be selected by the PIC. There will need to be some sort of encoding done by the PIC on this data. PIC The PIC will take the data from the MUX and encode it into a format with error protection for transmission. The output will be digital as to conform to the LINX transmitter. The PIC will have to be a light weight cost effective chip, as to minimize the transmitter’s price and dimensions. LINX Transmitter The transmitter will take the data from the microcontroller and act as the communication between the transmitter and receiver blocks of this project. The transmitter will transmit the digital data provided by the accelerometers from the PIC. This will probably be the HP3 series transmitter. Power The lightweight battery will provide the power for this device. Because of the short life time of a ball a battery should suffice as the only power needed. Other options are to use the kinetic energy of the ball as a source for power. If needed a magnetic switch maybe used as an on/off to conserve power.

Receiver Design
I. Block Diagram

LINX

PIC

MAX232

II. Description LINX Receiver This will probably be the Linx HP3 series receiver. It will take the data and output it to the PIC. PIC This PIC error detects and then transmits the data via the max232 level converter. The digital input will be verified before it is transmitted to the pc for data analysis. MAX232 This component will interface with the PC using a serial port.

Analysis/Storage PC
I. Block Diagram

Calibration/ Initialization Serial Port Analysis Storage DISPLAY

II. Description Calibration/Initialization The data will need to be initialized at some point so that a reference can be used as an initial position and a reference velocity of zero. All movements will then be manipulated from this point. Analysis The acceleration data will be integrated to find velocity and position. With this the balls position on the field will be displayed and first downs, touchdowns, and if the ball is touching the ground will be noted. Storage The data will be stored so that replay can be implemented; however our programs will not have that capability. Display A two dimensional display will be outputted to the screen of the pc.

Performance Requirements
Material Requirements The transmitter must be made as light as possible to minimize disturbance to the balls performance. Less than 80 grams would be good, but the lighter the better. However, the design must keep in mind durability. As well as cost effectiveness. There are a number of balls used in a single football game. So the transmitter must be relatively inexpensive. The other parts of the project can be as big and as fragile as necessary as they will not Power Requirements The battery must be able to last through the course of at least one game (at least 4 hours). Transmitter/Receiver The transmitter must be able to transmit a distance slightly more than the area of a football field. If the receiver is place at the middle of the field then the distance only needs to be around 170’. However a greater range would allow for more flexibility in the position of the receiver adding to convenience. Technical Requirements The football position must be known at all times. Thus the sampling rate must be as high as possible. A rate of 200Hz would be nice, but will depend on the price of the materials. The sensors should be within 1% accurate. Summary I. Less than 80 grams II. Battery life at least 4 hours III. Transmitter distance of over 170’

IV. V.

Sampling rate of at least 200Hz Sensors 1% accurate

Verification
Testing Procedures The general process for testing will be to put each of our components (accelerometers, microcontrollers, transmitter/receiver) on solder-less protoboards and test them on an individual basis, before fabricating our final circuit. Accelerometer Chips: We must measure the outputs of each accelerometer for varying inputs, (test limits of g’s). This will allow us to calibrate each accelerometer to match. Additionally we can use a centrifuge to measure linearity and sensitivity. LINX Transmission: The transmission and reception of a signal can be verified by using a test signal to check the quality of transmission at varying lengths. Receiver Software: The implemented software can be tested by inputting test data representing ball movements to verify that the software is displaying correctly.

Tolerance Analysis
The most pressing component of the design will be the accelerometer chips. The raw data acquired by these chips will need to operate within a large temperature range. Football games are played in the summer and winter months in indoor and outdoor stadiums. Therefore, the football experiences a large array of temperature states. The sensors will also need to withstand the impact a football experiences during the course of a game. The sensors will need to be able to transmit data while the football is accelerated at the high speeds experience during play. While varying the temperature we will test the output of the sensors while the accelerometers are in motion. These values, especially at the extremes of the temperature range, will determine where our tolerances lie. The balls will need to be tested with measured forces being applied to the ball, and the sensors will need to continue to operate properly. The chips will also need to be tested to determine that they are in fact outputting the velocity of the ball accurately. This aspect can be confirmed with other speed analysis instruments.

Cost and Schedule
Labor Each of us will work 6 hours a week for 14 weeks this semester. At a rate of $30/hour, and two team members the total labor cost equates to:

($50/hour)*(8 hrs/wk)*(14wks)*(2 people)*(2.5) = $28,000 Cost Analysis Part Accelerometer Chip Microcontroller RF Transmitter RF Receiver Antenna Battery PC Serial Cable Miscellaneous Labor

Qty 3 2 1 1 1 1 1 1

$/Item 10 2 2 2 2 3 1000 5

Subtotal 30 4 2 2 2 3 1000 5 10 28000 Total: $29,058

Part Status Part Accelerometer RF TransReceiver MicroController Mux

Manufacturer Analog Devices Linx Technologies Motorola -

Model No. ADXL210 HP3-Series PIC12F675k 8x1 Mux

Status To be Ordered Available at Lab Available at Lab Available at Lab

Schedule Week of Activity 1/23/05 Initial ideas 1/30/05 Research Design/Ordering 2/6/05 Parts Receiving Parts 2/13/05 Begin Testing Testing and 2/20/05 Design 2/27/05 Start building 3/6/05 Complete Build 3/13/05 Making it Work Testing and Software 3/20/05 3/27/05 Finish Up 4/3/05 Fix up 4/10/05 Retest/Debug 4/17/05 Retest/Debug 4/24/05 Presentation

Kavin Arumugham Initial ideas Communication/PICs/Battery Base Station Components Test Base Station Components Build Base Station Complete Base Station Integration of System Test/debug Debug while developing display software Finish Software portion Continue Debugging Throw Stuff Give Up Presentation

Arjun Majumdar Initial ideas Sensors/MUX/PICs Football Chip Components Test Football Chip Components Build Football Chip Complete Football Chip Integration of System Test/debug Debug while developing data acquisition software Finish Software portion Continue Debugging Throw Stuff Give Up Presentation


				
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