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Football Wristband for Measuring Throwing Speed Group 18 Kevin He & Darryl Ma ECE Senior Design November 30, 2006.

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Presentation on theme: "Football Wristband for Measuring Throwing Speed Group 18 Kevin He & Darryl Ma ECE Senior Design November 30, 2006."— Presentation transcript:

1 Football Wristband for Measuring Throwing Speed Group 18 Kevin He & Darryl Ma ECE Senior Design November 30, 2006

2 Motivation Provides a cost effective solution for measuring speed Does not require a dedicated operator Can be applied to other sports: baseball, boxing, cricket, etc.

3 Objectives Accuracy within 10% of measurements obtained from radar gun Weighs less than 500 grams Lasts up to 5 hours per battery/charge Temperature is within 3 C of ambient Able to measure a velocity range of 0mph to 70mph in increments of 1mph

4 Original Design Overview Hardware Power Supply Module, Pressure Sensor, Accelerometer, LCD, PIC Microcontroller Software PIC programming for user interface and speed calculation algorithm

5 Block Diagram Block Diagram of the Device

6 System Schematic

7 Original Hardware Design Power Supply Module Converts 3V from coin cell battery to stable 5VDC Pressure Sensor Informs microcontroller when the ball is in the users hand and when the ball has been released Accelerometer Measures acceleration of the wrist LCD Displays velocity and user prompts PIC Microcontroller Performs integration function to calculate speed

8 Power Supply Module Battery Rating: 160mAh Converts 3VDC to a stable 5VDC Total Current Drain: 20-22mA Schematic of Power Supply Module

9 Power Supply Output V max = 5.445V V average = V V min = 5.416V V ripple = 14.69mV Voltage output waveform from power supply module with 120k load resistance

10 Pressure Sensor Polyester variable resistor (32k to 420k) Used voltage divider circuit to convert varying resistances into varying voltages 5VDC Schematic of Pressure Sensor CircuitPressure Sensor

11 Pressure Sensor Resistance Vs Voltage V high => hand unoccupied V low => ball in hand Output Voltage Vs Pressure Sensor Resistance Resistance of Pressure Sensor ()

12 Accelerometer ±5g ADXL320 Dual Axis Accelerometer 5V supply with 2mA current drain Capacitors attach across output terminals for signal conditioning Accelerometer Capacitors for signal conditioning

13 Accelerometer Sensitivity Verify datasheet sensitivity value of 312mV/g Voltage output from accelerometer when dropped

14 Accelerometer Orientation Voltage outputs change depending on orientation

15 LCD Displays user prompts and final ball velocity 16X2 RT1602C character LCD 5V supply with 1mA current drain

16 PIC Microcontroller PIC16F877A Performs integration of acceleration input to calculate ball velocity 5V supply with 8mA current drain Operating frequency: 8.00MHz

17 Original Software Design Written in PIC-C Purpose Obtain Inputs from Pressure Sensor and Accelerometer Calculate Velocity Output results to LCD

18 Original Flow Chart

19 Riemann Sum Acceleration to speed conversion a(t) = acceleration function v(t i ) = velocity at time, t i Positive and negative accelerations cancel to zero at apex of wind-up

20 Baseline Detection System When the PIC senses a relatively stable signal, it resets the net velocity to zero Integration sum is reset to zero here. Voltage output from accelerometer when simulating a throw

21 Debugging Major Problems we encountered: 1) Poor battery life 2) PCB/Protoboard Issues 3) Inconsistent Results

22 Poor Battery Life Battery rating of 160mAh and current drain of 21mA suggests battery life of ~8 hours. Actual battery life only about ~4 hours, with frequent fadeouts Traced problem to battery brand Energizer is the way to go!

23 PCB/Protoboard Issues Main issues were related to durability Protoboard wires and components often came loose Solution: Make PCB PCB wire pads were often stripped of copper lining Solution: Use 30 gauge wires to reinforce connections

24 Inconsistent Results Causes Explored 1) Accelerometer output noise 2) Insufficient sample size 3) Accelerometer Orientation 4) Pressure Sensor Sensitivity

25 Accelerometer Output Noise Measurement of the accelerometers axis show a large uncertainty in the output voltage. The uncertainty is on the order of ~1V, as seen on the graph. Output voltage waveform from accelerometer when simulating a throw

26 Accelerometer Noise Solution Stability Testing: Output from PIC stable within 9.8mV Testing Accuracy of PIC Reading from Accelerometer Our solution was to add capacitors across the power terminals of the PIC, oscillator, and accelerometer. This further stabilized the input voltage waveform, which helped the accelerometer output consistent results. Output voltage waveform after adding capacitors to PIC, oscillator, and accelerometer

27 Insufficient Sample Size What is the processing time per sample? Are there enough samples to perform an Riemann Sum integration?

28 Accelerometer Orientation Changing the accelerometer orientation changes plane of acceleration

29 Pressure Sensor Sensitivity Is the pressure sensor sensitive enough to detect the football? Lab tests show that even a gentle grip causes a sizeable voltage drop However, while actually throwing a ball, the user may loosen his grip even though the ball is still in his/her hand

30 Removal of Pressure Sensor Radar Gun Speed (mph) Device Speed (mph) Trial # Trial # Trial # )The trials below represent three out of ten trials that returned results. The other seven trials produced no measurement due to insufficient number of samples. The number of samples is directly controlled by the pressure sensor. 2)Inhibits throw 3)Reduces production cost significantly

31 Threshold Algorithm Threshold Starts integrating as soon as the 1.4g threshold is reached and continues to integrate until acceleration falls below this threshold Eliminates need for pressure sensor and baseline detection Will give relative velocity rather than exact velocity, so offset factor needed

32 Velocity Correction Factor Why is it needed? Threshold algorithm only measures acceleration beyond a certain limit, so not all acceleration is captured The acceleration per sample is sqrt(x 2 + y 2 ), but taking the square root every sample reduces the number of total samples we can take, so we only used x 2 + y 2

33 Velocity Correction Factor We know there is a correlation between the device speed and radar gun speed, so we need to apply an offset to make them equal The velocity is: The offset factor was determined solely based on experimental data. The speeds that we validated were the ones we could obtain with the radar gun (25mph – 40mph). Our final equation including offset is:

34 Velocity Correction Factor Measurements from Radar Gun (mph) Measurements from our device (mph) – without correction factor (Velocity * ) Measurements from our device (mph) – with correction factor Trial # Trial # Trial # Trial # Trial # Trial # Trial # Trial # Average percentage difference Without Correction Factor: 17.9% With Correction Factor: 6.68% Std. Dev. of percentage difference Without Correction Factor: 3.25% With Correction Factor: 2.61%

35 New Flowchart

36 Summary of Final Design Original Power Supply Circuit Original LCD Added capacitors to clean up accelerometer output Removed Pressure Sensor Modified Velocity Algorithm

37 Verification Radar Gun Vs Wristband Correlation Check Tolerance Analysis Temperature Measurements

38 Radar Gun Vs Wristband Radar Gun Measurement Measurement from Device Percentage Difference % % % % % % % % % % Percentage Difference Average: 4.507% Std Dev.: 3.381%

39 Correlation Check Since the radar gun only measured speeds greater than 25mph and we were not able to throw the football faster than 38mph, we performed a correlation check to make sure there was some correlation between the relative speed of the arm and the measured throw speed.

40 Correlation Check Results Relative SpeedTrial #1Trial #2Trial #3Trial #4Trial #5 Slow6mph3mph4.6mph4.2mph7.6mph Medium11.1mph13.1mph10.3mph12.5mph14.4mph Fast30.2mph28mph23.7mph30.6mph27.1mph Results show a definite correlation between the relative speed of the arm and the measured throw speeds (throws were performed empty-handed)

41 Tolerance Analysis Concern: Accelerating over 5g could damage the accelerometer or other components Voltage = 1.891V Sensitivity = 0.312V/g g = Voltage/Sensitivity g = 5.66g Tolerance Analysis on Y-Axis

42 Tolerance Analysis Waveform shows no saturation at accelerations greater than 5g and when integrated back into device, there were no adverse effects. Voltage = 2.031V Sensitivity = 0.312V/g g = Voltage/Sensitivity g = g Tolerance Analysis on X-Axis

43 Temperature Measurements Room Temperature: 24.8°C Device-Wristband Surface: 26.8°C Wristband-Skin Surface: 26.4°C Normal Skin Temperature: 32.9°C Fulfills our performance requirement of ±3°C of ambient temperature

44 The Wristband

45 SWOT Analysis Strengths: Easily removable and comfortable Powered by one 3V coin cell battery Cost effective Large range of measurement Weaknesses: Inconsistent results due to human variation Slightly inhibits throw Measures acceleration in one plane Opportunities: Useful for other sports applications Threats: Low consumer demand

46 Comparison with Radar Gun CostAccuracyPrecisionEase of UseMeasurement Range Battery Life Radar Gun $85 - $400Within +/- 0.5mph +/- 1mphRequires dedicated operator Relative angle to ball should be less than 15 degrees for best accuracy ~20 hours using specialized batteries, or 6 AA batteries Our Device $80 for prototype, $45 if mass- produced Within +/- 10% of Radar Gun +/- 0.2mphDoes not require dedicated operator Accuracy independent of ball path ~4 hours using a single 3V coin cell battery

47 Ethical Considerations Safety Temperature Electrostatic Discharge (ESD) Being honest/realistic about what our device is capable of

48 Future Steps More accelerometers to achieve absolute acceleration, and enable more accurate measurements Convert all parts to surface mount components to reduce device size Improve durability Improve battery life Apply for a Patent

49 Credits Ms. Hye Sun Park Mr. Mark Smart Professor Jonathan Makela Coach Dan Hartleb & Coach Eric Snider

50 Questions?


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