1 / 50

Football Wristband for Measuring Throwing Speed

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

lester
Download Presentation

Football Wristband for Measuring Throwing Speed

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

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 user’s 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 • Vmax = 5.445V • Vaverage = 5.4305V • Vmin = 5.416V • Vripple = 14.69mV Voltage output waveform from power supply module with 120kΩ load resistance

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

  11. Pressure Sensor Resistance Vs Voltage • Vhigh => hand unoccupied • Vlow => ball in hand Resistance of Pressure Sensor (Ω) Output Voltage Vs Pressure Sensor Resistance

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

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

  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 accelerometer’s 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 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 Stability Testing: Output from PIC stable within 9.8mV Testing Accuracy of PIC Reading from 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 • 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. • Inhibits throw • 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(x2 + y2), but taking the square root every sample reduces the number of total samples we can take, so we only used x2 + y2

  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: • Our final equation including offset 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).

  34. Velocity Correction Factor 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 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 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 ∆Voltage = 2.031V Sensitivity = 0.312V/g g = ∆Voltage/Sensitivity g = 6.5096g Tolerance Analysis on X-Axis Waveform shows no saturation at accelerations greater than 5g and when integrated back into device, there were no adverse effects.

  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. Strengths: Easily removable and comfortable Powered by one 3V coin cell battery Cost effective Large range of measurement SWOT Analysis 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

  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?

More Related