1. University of Pennsylvania Department of Electrical and Systems Engineering ABSTRACT: Quantifying and measuring certain aspects of a golf swing is a helpful tool for any golfer. Currently, the only way to achieve this is by traveling to an indoor, controlled environment rigged with complex sensors and having a system contained within measure the swing. Not only are these facilities relatively sparse, but they are prohibitively expensive to the average golfer. The solution to these problems is a series of sensors and the necessary interfacing circuitry, integrated onto a golf club. The system is designed to measure the velocity of the swing, the angle the ball is launched at and the region of the club face where impact occurs. Accuracy, unobtrusiveness and portability are the key factors for this system and they drove the approach to the project. AUTHORS: Seth Charlip-Blumlein Shehzad Khan ADVISOR: Professor Jan Van der Spiegel DEMO TIMES: April 21 st, 11-11:30am & 1:30-3pm GROUP 11 Engineering a Better Golf Swing Sensors and Calibration Methods Velocity Measurement: ADXL150 Accelerometer The ADXL150 has a 50G measurement range with on chip filters and zero G nulling features. As there were no high-G calibration methods available, it was calibrated by attaching it to a pendulum and connecting the output to an integrator. By varying the pendulum’s amplitude, the peak velocity was calculated with mechanics equations and the output voltage was measured. Angle Measurement: ADXL320 Accelerometer The ADXL320 is used as an inclinometer via it’s DC response to gravity. It was calibrated by precisely measuring angles in the range of -45° to 45° in increments of 1° (via right triangle trigonometry) and recording the lookup table of the output voltages for use in the display unit. Contact Region Measurement: Polyvinylidene Fluoride Sheet PVDF is a material that produces a voltage between its two metalized surfaces when a force is applied. No calibration was necessary for this material, as precise output values weren’t important for it to function as an “on/off” contact sensor. System Block Diagram Transmission Diagram System Design The system is broken down into three overarching subsystems: on club sensors, an on club communication circuit and an off club display unit. Sensors and interfacing circuitry The sensor blocks consist of the actual sensors to measure club velocity, angle and contact point, as well as the circuitry needed to condition the values for transmission. User signals and coordination between the conditioning circuits ensure that the data is collected properly and captured at the correct point in the swing. Launch Angle Measurement: The angle of the launch is measured as the player tees up the ball and prepares for the swing. It is measured by a precise inclinometer to 1 ° of accuracy, and the value is held with a sample/hold circuit until transmission. Club Speed Measurement: A high G accelerometer is mounted on top of the club head with its axis of sensitivity in the direction of the swing. The acceleration values generated by the accelerometer are passed to the conditioning circuit, which integrates and scales them to get a velocity reading. This value is captured by a sample/hold circuit and held until transmission. The velocity is measured to an accuracy of 1 mph. Contact Region Measurement: The contact sensors themselves are strips of piezo-electric film. When the ball strikes one of the four strips, a peak detector circuit holds the output voltage and sets a flip-flop. The flip-flop values are converted to one analog value in preparation for transmission and are also used to generate the signal to capture the velocity value of the club. Communication System The communication system makes use of Pulse Width Modulation to transmit the data. For each measurement to be transmitted, the duty cycle of a 300 Hz square wave is changed proportionally to the voltage captured. The square wave is fed to an IR LED, which transmits the data to the display unit. Since signals the three signals only take 1/300 th of a second each to transmit, full data transmission is accomplished in 10 ms. Display Unit The display unit is composed of an IR receiver, an HC11 microcontroller, two 4-digit LED displays (for the velocity and angle readings), 4 LEDs (for the contact region) and user input buttons. It receives the input from the club and displays the data to the user, who can scroll through up to 500 stored measurements from the current golf session. (clockwise from left: PVDF Strip, ADXL150 Accelerometer, ADXL320 Evaluation Board) Inclinometer Output Voltage vs. Inclination