AUTOMATED(NBA(GAME(CLOCK(
STOPPER(
By
Rahul Harikrishnan
Pranav Saboo
Saud Tahir
Final Report for ECE 445, Senior Design, Spring 2022
TA: Akshatkumar Sanatbhai Sanghvi
04 May 2022
Project No. 36
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This project utilizes ambient light sensing technology mounted on a basketball net to stop the game clock when a shot is made.
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AUTOMATED NBA GAME CLOCK
STOPPER
By
Rahul Harikrishnan
Pranav Saboo
Saud Tahir
Final Report for ECE 445, Senior Design, Spring 2022
TA: Akshatkumar Sanatbhai Sanghvi
04 May 2022
Project No. 36
ii
Abstract
This project utilizes ambient light sensing technology mounted on a basketball net to stop the game clock when a shot is made. Ultimately, every subsystem of the final design was verified through unit testing, and the system correctly classifies over 90% of attempted shots as either made or missed. The game clock stops on made shots and continues running for missed shots. Although the resulting system is too sensitive to fluctuations in standard environments, the constant lighting conditions within a basketball stadium would alleviate this concern.
1. Introduction
1.1 Purpose and Functionality Within the last two minutes of an NBA game, the game clock is supposed to stop immediately after each made shot. This process is currently done manually by a game clock operator. However, as viewers, we have seen delays in this manual stopping of the clock due to human reaction speed. An example of this can be seen in Game 6 of the 2013 finals where Ray Allen hit a game-tying 3 pointer with 5.2 seconds left on the clock. However, after looking at the replay we can see that the ball actually clears the net with 5.5 seconds left on the clock [1]. Another example can be seen in game 5 of the 2021 Finals where Khris Middleton makes a layup in a close game. The clock stops at 27.2 seconds, but when looking at the replay we see that the clock should have stopped at 27.5 seconds [2]. Three-tenths of a second may seem like an insignificant amount of time, but according to the Trent Tucker rule [3], 0.3 seconds is the minimum amount of time required to inbound the basketball and attempt a shot. If the game clock displays less than 0.3 seconds approaching the end of the game, the shot will be waived off. There have been numerous similar instances of delayed clock stoppage throughout past seasons and playoffs. Multiple delays within the same game can mount to create enough time for teams to design and run complex plays. In summary, an accurate stoppage of the clock is crucial for close games as every three- tenths of a second is enough time for another possession, which can influence the outcome of the game. To solve this problem, we developed a system that tracks when the ball goes through the hoop and immediately stops the game clock. This was accomplished by using an ambient light sensor system integrated into the net. The key functionality of our solution is to detect a made shot, which is done by measuring the decrease in ambient light level associated with a made shot, and subsequently stop the clock within 0.3 seconds. This marks a significant improvement over the average human reaction time.
1. 2 Subsystem Overview Figure 1. Block diagram of system. The product is broken down into four main subsystems: Power, Sensor, Control & Processing, and Clock. The Power Subsystem is responsible for providing the appropriate voltage to all components in each subsystem. The Sensor Subsystem is responsible for detecting the ambient light level at the bottom of the net and converting this light level to a voltage that is sent to the Control & Processing Subsystem. The Control & Processing subsystem is responsible for analyzing the voltage input from the Sensor Subsystem and sending a signal to stop the game clock when this voltage input is below a certain threshold (which indicates a made shot). The Clock Subsystem is responsible for displaying the time left in the game. The clock display will stop when it receives the aforementioned signal from the Control & Processing Subsystem.
2.2 Design Description Figure 2. Visual aid of final design. Figure 2 shows a visual representation of our system. The ambient light sensor will be attached at the bottom of the net and will connect to the Sensors PCB of the Control & Processing Subsystem. The two PCBs of the Control & Processing Subsystem will be attached to the back of the backboard in a box. This will ensure that the Control & Processing Subsystem will be protected from the basketball and any game play activities. The Clock PCB controls the clock display which is mounted at the top of the backboard.
2.2.1 Power Subsystem
The Power Subsystem consists of a 12 V DC power supply [5] and a linear voltage regulator [6]. The linear regulator converts the 12 V provided by the DC power supply to 3.3 V, which is compatible with all our components. We considered using a buck converter in place of a linear regulator, but we eventually decided that the higher efficiency of the buck converter was not worth the tradeoff of a higher power supply noise and complexity for our system.
Figure 3. Schematic of power subsystem.
2.2.2 Sensor Subsystem
The Sensor Subsystem is responsible for detecting the ambient light level at the bottom of the net and converting it to a voltage output that is sent to the Control & Processing Subsystem. This subsystem consists of a photoresistor, which is part of a voltage divider circuit with a fixed 10 kΩ resistor, mounted on a small PCB at the bottom of the net. The schematic corresponding to this design can be seen in Figure 4. The photoresistor has a resistance of 2 kΩ at very high ambient light levels (~100 lux) and 100 kΩ at very low ambient light levels (~1 lux) according to its datasheet [ 7 ]. Utilizing the voltage divider equation below (1), we determined that the output voltage can take on any value between 0.3 V (at ~ lux) and 2.75 V (at ~100 lux). A higher ambient light level indicates either a missed shot or an empty basket. In this case, the resistance of the photoresistor will be lower, and the output of the voltage divider circuit shown in Figure 4 will be closer to the maximum of 2.75 V. On the other hand, a lower ambient light level indicates a made shot. In this case, the resistance of the photoresistor will be higher, and the output of the voltage divider circuit will be closer to the minimum of 0.3 V.
Figure 5. Schematic of Control & Processing Subsystem.
2.2.4 Clock Subsystem
The Clock Subsystem consists of a 4-digit 7-segment display with an I2C backpack converter [9]. The I2C backpack converter is a PCB that converts the I2C signal sent from the clock microcontroller to an array of traditional 7-segment display signals. Initially, we were considering only using a traditional 4-digit 7- segment display but determined that the limited number of outputs from the ATTiny45V microcontroller did not allow us to set each diode segment of every digit separately. To reduce the number of required outputs from the clock microcontroller, we reasoned that the use of only two outputs in I2C communication (SDA and SCL) would satisfy our requirements. Figure 6. Schematic of Clock Subsystem.
Table 4. Clock and Sensor Output on Made Shots from 18° Increments with Threshold of 1.65 V (Req. 1) Position of Shot (°) Sensor Voltage Output (V) Clock Output Verified? 0 1.243 Stops Yes 18 0.984 Stops Yes 36 0.865 Stops Yes 54 0.844 Stops Yes 72 1.140 Stops Yes 90 1.321 Stops Yes 108 0.994 Stops Yes 126 1.012 Stops Yes 144 0.869 Stops Yes 162 1.042 Stops Yes 180 1.003 Stops Yes Table 5. Clock and Sensor Output on Missed Shots from 18° Increments with Threshold of 1.65 V (Req. 1) Position of Shot (°) Sensor Voltage Output (V) Clock Output Verified? 0 1.888 Running Yes 18 1.936 Running Yes 36 2.342 Running Yes 54 2.270 Running Yes 72 2.242 Running Yes 90 2.045 Running Yes 108 3.036 Running Yes
126 1.978 Running Yes 144 2.784 Running Yes 162 2.132 Running Yes 180 2.457 Running Yes 3.3 Control & Processing Subsystem As detailed in Table 13 in Appendix A, the requirements of the Control & Processing Subsystem specify that the data signal output from the sensor microcontroller must be high when the sensor is triggered in a fashion that indicates a made shot and must be low when the sensor output does not indicate that a shot is made. Furthermore, the signal input at pin PB1 of the clock microcontroller must be a logical high when the output of the sensor microcontroller is a logical high, and vice versa. Tables 6 and 7 below detail the results from the verification process for each requirement. Table 6. Sensor Microcontroller PB1 Voltage Output for Threshold of 1.65 V (Req. 1) Input Voltage to ADC Pin (V) Expected Voltage Output (V) Measured Voltage Output (V) Verified? 0 2.4 - 3. 3 3.26 5 Yes
- 5 2.4 - 3. 3 3.27 7 Yes
- 4 0 - 0. 5 0.12 2 Yes
- 3 0 - 0. 5 0.13 1 Yes Table 7. Clock Microcontroller Voltage at Pin PB1 (Req. 2) Logical Output of Pin PB1 of Sensor Microcontroller Expected Voltage at Pin PB1 of Clock Microcontroller (V) Measured Voltage at Pin PB1 of Clock Microcontroller (V) Verified? Low 0 - 0.5 0.118 Yes High 2.4 - 3.3 3.267 Yes
4. Cost & Schedule
4.1 Parts Table 9. Cost of all Parts. Description Manufacturer Part # Quantity Cost (per unit) DC Power Supply Gravitech 12V1A- 25 - POS- WALL
Linear Voltage Regulator Texas Instrument LM117H 1 $10. Microcontroller Microchip Technology
ATTINY45V-
10XU
4 digit 7-segment Display Adafruit 879 1 $9. Total for Required Parts in Final Design
Ambient Light Sensor Lite-On Inc. LTR-329ALS- 01 10 $0. Spare Microcontroller Microchip Technology
ATTINY45V-
10XU
Spare Linear Voltage Regulator Texas Instrument LM117H 1 $10. I2C Multiplexer Adafruit TCA9548A 1 $6. Mini Hoop [1 0 ] Sklz 088 - 08 - 0037 1 $29. Total for All Parts Used Throughout Design Process
4.2 Labor $39.86/person/hour x 3 people x 10 hours worked/week * 13 weeks worked = $15,545.40 Total [ 11 ]. 4.3 Schedule Table 10. Individual Work Schedules. Week Work Pranav Rahul Saud 1 Submit RFA Brainstorm Idea, Create RFA with Rahul and Saud Brainstorm Idea, Create RFA with Pranav and Saud Brainstorm Idea, Create RFA with Rahul and Pranav 2 Submit Project Proposal and Talk to Machine Shop Meet with Akshat, meet with machine shop, research sensors to use, and create project proposal with Rahul and Saud Meet with Akshat, meet with machine shop, research sensors to use, and create project proposal with Pranav and Saud Meet with Akshat, meet with machine shop, research sensors to use, and create project proposal with Rahul and Pranav
3 Work on Design Document Work on introduction, power subsystem, sensor subsystem, cost analysis, schedule and citations Work on introduction, sensor subsystem, microcontroller subsystem, tolerance analysis and citations Work on block diagram, physical design, clock subsystem, ethics, and citations 4 Submit Design Document and Order Parts Revise clock subsystem, microcontroller subsystem, and tolerance analysis, and citations. Work with Rahul and Saud to order parts. Revise block diagram, physical design, clock subsystem, ethics, and citations. Work with Pranav and Saud to order parts. Revise introduction, power subsystem, sensor subsystem, cost analysis, schedule and citations.Work with Rahul and Pranav to order parts. 5 Finalize PCB Layout and Order PCB Ensure that the schematic matches the PCB layout. Order PCB. Check PCB layout for trace bend angles, mounting hole locations, ground planes, stitching vias. Make sure reasonable part sizes are chosen for PCB. Check PCB layout for connectors for all incoming and outgoing connections, thicker traces for power delivery, labeling on silkscreen layers and extra pins for debugging. 6 Build and Test Power Subsystem, Complete Teamwork Evaluation and visit Machine Shop Build the linear voltage regulator with Rahul and Saud, and test using an oscilloscope. Complete teamwork evaluation and visit machine shop with Rahul and Saud. Build the linear voltage regulator with Pranav and Saud, and test using an oscilloscope. Complete teamwork evaluation and visit machine shop with Pranav and Saud. Build the linear voltage regulator with Rahul and Pranav, and test using an oscilloscope.. Complete teamwork evaluation and visit machine shop with Rahul and Pranav. 7 Solder all Components to PCB and Complete Individual Progress Reports Solder microcontroller and connections from power subsystem and complete individual progress report. Solder connections from ambient light sensor and complete individual progress report. Solder connections from game clock display and complete individual progress report. 8 Test and Debug Overall System Perform unit tests, test all cases and make necessary adjustments with Rahul and Saud. Perform unit tests, test all cases and make necessary adjustments with Pranav and Saud. Perform unit tests, test all cases and make necessary adjustments with Rahul and Pranav.
5. Conclusion
5.1 Accomplishments By the end of the project, we were able to successfully verify every subsystem, as outlined within our Design Verification section, as well as all high-level requirements. We were successful in ensuring that the delay between a made shot and the clock stoppage is less than 0.1 seconds, which we tested through recording slow motion footage of the system. Additionally, we achieved over 90% accuracy for classification of the shots that were attempted. 5 .2 Uncertainties Although our system achieves over 90% accuracy when classifying shots as “made” or “missed” based on the ambient light level, the primary concern associated with our solution is the degree of accuracy due to the strict standards of the NBA. In order for our system to be ready for implementation in an NBA arena, we would need to prove that we can achieve over 98% accuracy with a sample size of over 10,000 shots at recreational levels of basketball. The results of this experiment may require us to modify our implementation. Furthermore, the results of our system are very sensitive to fluctuations in the lighting of the environment. Events such as a light being turned off or a cloud covering the sunlight from a window would require recalibration of the sensor. However, we believe that an NBA arena would provide a consistent lighting environment for the duration of the game, so this concern could be alleviated. 5 .3 Ethical considerations As engineers, we have an obligation to ensure that our products and building practices adhere to the IEEE Code of Ethics. Although our product does not pose any significant safety issues, we have to account for other ethical standards. Specifically, our device cannot be tampered with to unfairly benefit one party, in accordance with standard I.4 in the IEEE Code of Ethics. Additionally, we will seek and accept criticism of our technical work and make realistic claims based on the data we collect through extensive testing, in accordance with standard I.5. Moreover, we will design an enclosure for our PCBs with the game clock such that we avoid injuring players, in accordance with standard II.9. This standard also applies to the installation of the system on a full-size basketball court. Finally, we will hold each other accountable to always adhere to the IEEE Code of Ethics, including the entire design and build process as well as after we present our finished product, as stated in standard III.10. [ 12 ] In addition to the IEEE Code of Ethics, we will design our product to be compatible with NBA league regulations and ensure that its implementation does not disturb the spirit of the game. As such, our system must be consistent in average time delay and accuracy between the two hoops on the basketball court. Furthermore, any given device has to have a consistent delay in stopping the game clock. Moreover, the system must not significantly disturb the flow of the shot and must adhere to NBA league regulations regarding equipment. Along with the IEEE Code of Ethics, this ensures that we uphold the highest ethical standards. 5 .4 Future work Much of the future improvements involve cohesion with the operation of the game clock. This would include the ability for the game clock operator to resume the clock upon inbounding of the ball, which
occurs after every made shot. Also, the game clock operator would be given the option to override the displayed clock value in the case that a player steps out of bounds, commits a foul, or the system malfunctions. Moreover, we would implement automatic detection to determine if the game is in the last two minutes, so that the system would not have to be manually turned on at that time. Along with this, we would like to create a second system to simulate real game clock management and ensure that both systems are working identically and without conflict.