1. Persistence of Vision LED Sphere Display
Group 26
Michael Ling
Lunan Li
Jiale Quan
Hi everyone and thank you for coming to our presentation today. I am Michael, this is Lunan, this is Jiale, we are group 26 and our project is the Persistence of Vision LED Sphere Display

2. Introduction
A Spinning Ring of LEDs Capable of Creating a Persistence of Vision (POV) Effect at 24 Frames Per Second (FPS)
A Visually Appealing and Entertaining Way to Display Images and Animations
Potential New Digital Marketing Method
In simple words, our project is a ring of LEDs that spins at high enough speeds such that it is capable of creating a persistence of vision (POV) effect at 24 frames per second. This effect refers to the optical illusion that occurs when multiple discrete images blend into a single image or animation. We wanted to invoke this effect at 24 FPS because that is approximately what movies are shot at, so we wanted to be able to create cinema-quality images/animations, and we chose to do this project to develop and create a visually appealing and entertaining way to display images and animations that could potentially be used as a new way to digitally market things.

3. System Overview Mechanical
Custom-Built LED Ring Stand (ECE Machine Shop)
Slip Rings
DC Motors
Hardware
Microcontroller
Motor control circuit
8-Bit RGB LEDs
Software
2DOF Algorithm
GUI
Our project was split up into three main disciplines: mechanical, hardware, and software. I took responsibility for the mechanical portion, Jiale did the hardware work, and Lunan developed the software. Obviously there was a lot of overlap between the three of us during the semester, but these were our “primary” responsibilities.

4. The POV LED Sphere System
LED Ring
Slip Ring
Motor Driving LED Ring
Spinning Plate
Here you can see the physical portion of our project, and to help you get a sense of what is what, the major mechanical and hardware parts are highlighted, with the exception of the Hall Effect Sensors we used, which Jiale will talk about later.

5. The POV LED Sphere System
TIP Transistors
Slip Ring
Microcontroller PCB
Motor Driving Spinning Plate
This pictures shows the inner workings of our display. We decided to mount everything internally because we wanted the finished product to look nice and clean. The machine shop did a fantastic job giving us enough space to internally mount all of our components.

6. System Overview
This is a block diagram of our system. We used two separate power sources to drive our system. The 5V source is used to drive our sensors, microcontroller, and LED Strip while the 12V source is used to drive both of our motors. Since each motor will require a different voltage, we used two TIP Transistors to control the voltage supplied to each one. The Hall Effect Sensors will then allow the microcontroller to calculate the RPM and orientation of the LED Ring and the Spinning Plate. Using this data, the microcontroller then drives and refreshes the LED Strip mounted on the LED ring such that the POV effect occurs.
But in order for all of this to happen, the LED Ring stand needed to be made...

7. Mechanical Overview Custom Design LED Ring Stand
Two Degrees of Freedom
Stable Enough for High RPM
Manufactured by the ECE Machine Shop (David Switzer)
LED
Ring
Designing a stand that is stable enough to spin with two degrees of freedom at high RPMs was no easy task; however, with the help of David Switzer, we were able to create a beautiful display. Two DC motors were required to spin the wheel in two directions, and two slip rings were needed to supply power and transfer data to the spinning LED Ring.
Spinning Plate

8. Theoretical Torque Calculations
The graphs show how much torque needs to be supplied to the Spinning Plate and LED Ring based on how much they weighed. The graph on the left depicts how the weight of the Spinning Plate will affect the necessary torque and current drawn by the motor to spin at 720 RPM, and the graph on the right does the same for the LED Ring at 30 RPM. In the end, the Spinning Plate weighed around 0.5 kg, and the LED Ring a mere 0.1 kg, requiring less than 5 oz-in of torque collectively. The motors collectively drew little over 1.5 Amps while both spinning at the necessary RPMs

9. DC Motors Necessary to Spin the LED Ring in Two Directions
720 RPM for Spinning Plate
30 RPM for LED Ring
64 Counts Per Rotation Encoder (Not Used)
Knowing how much torque would be needed to drive our display, I decided to use DC motors with a stall-torque of 84 oz-in and free-run speed of 500 RPM. To run the Spinning Plate at 720 RPM, a 1:2 gear ratio couplet was used to. And we actually first planned on using the motor’s built-in encoders to monitor the LED Ring’s RPM and position, but we soon realized that the position and orientation of the ring could not be calculate just with encoders. So we actually didn’t end up using them in the end.

10. Slip Rings
Transfer Power and Data Between Stationary and Rotating Parts
Transmit 12V to the LED Ring-Motor
Transmit 5V to the LED Strip and Hall Sensors
Able to Transmit Data (Design Change)
Transmit Data to the LED Strip
I also needed to get power and data to the LEDs. Two slip rings were used because they can easily transmit plenty of power between stationary and rotating objects. We originally didn’t plan on transmitting data through the slip rings because we didn’t they would be reliable when spinning at such high RPMs; however, we were pleasantly surprised to find out that we actually COULD transmit data to the LEDs when the display was spinning at 720 RPM.

11. Mechanical Achievements
Custom LED Ring Display Stand
Reliable Power and Data Transmission via Slip Rings
30 RPM for LED Ring
720 RPM for Spinning Plate
Overall the mechanical portion of our project performed well. It provided a convenient way for us to supply power and transmit data to the LED ring. It easily drove the LED Ring to 30 RPM, and it was able to spin the Spinning Plate at 720 RPM. However, at 720 RPM, the whole display really started to shake, which brings me to the next slide.

12. Future Mechanical Improvements
Drive the LED Ring Using a Stepper Motor
Slip Ring with 22 AWG Wires (instead of 28 AWG)
Redesign Mechanical Portion for Optimal Motor Placement
If a team were to work on this project in the future, I would suggest to create a better design that features better motor placement. Specifically the motor driving the LED Ring. I made the mistake of placing the motor a bit far from the axis of rotation, causing the display to shake at higher RPMs.
Driving the LED Ring with a stepper motor would allow for more accurate and reliable measurements of the LED Ring’s RPM and orientation
And finally, finding slip rings with 22 gauge wire would also save a lot of soldering and time. 28 gauge wire is extremely hard to work with breadboards and microcontrollers like the Arduino.
Overall, though, the mechanical portion of the project performed pretty well; and when it was finished it was finally time to start developing the hardware, which Jiale will now talk about.

13. Hardware Overview Microcontroller TIP transistor LED ring
Hall Effect Sensor
The hardware part consists of 4 subsystems, the micro-controller receives signals from hall effect sensors and after processing with the algorithm, then send control signals to Led strip and TIP transistor.

14. Microcontroller Microcontroller-Atmega 328P
Hall Effect Sensor(Horizontal)
Hall Effect Sensor(Vertical)
LED Data （SPI）
LED Clock（SPI）
TIP base (Horizontal)
First, we use the Atmega 328p chip as our micro-controller, it has 32 Kbyte flash memory and can run at 20 MHz operating frequency, with 6 analog and 14 digital Input and output pins, we use the digital pins to communicate with other peripherals. Highlight pin numbers.
PWM pulse width modulation
TIP base (Vertical)

15. This is the schematic of microcontroller PCB
This is the schematic of microcontroller PCB . For the right side we have the wires connecting the peripherals to the chip. To avoid approaching the device while spinning and upload the program, we use a bluetooth module to wirelessly send data to the chip. On the top, it is the power supply to the board. At left center, we have a external clock. Lets zoom in to see the detail.

16. Since the internal clock of the chip is only 8 MHz, we add a 16 MHz crystal oscillator as the external clock to speed up the data transmission. We also tested other higher frequency crystals, but they cannot pair with the bluetooth module which with 16 MHz

17. RPM and Limitations Higher RPM will achieve higher FPS
Higher RPM also has higher requirement for hardware
Data transmission
Safety issues while spinning
Desired FPS
Desired Spinning Plate RPM
12 (critical FPS to form POV effect)
360
24(optimal)
720
30(stabler and clearer)
900
Higher FPS, clearer and stabler image.
However there are hardware limitations that prevents us from reaching high RPM

18. Motor Control Circuit TIP120 - NPN Epitaxial Darlington Transistor
Using the TIP transistor, we can realize voltage adjustment across the motor from software side without change the actual voltage supply.
add a graph of TIP voltage

19. LED Ring
24-bit color
2-wire SPI protocol with 8 MHz for high speed data transmission
𝐷𝑎𝑡𝑎 𝑇𝑟𝑎𝑛𝑠𝑚𝑖𝑠𝑠𝑖𝑜𝑛 𝑆𝑝𝑒𝑒𝑑=𝑅𝑒𝑓𝑟𝑒𝑠ℎ 𝑅𝑎𝑡𝑒 × 32 𝑏𝑖𝑡𝑠 𝐿𝐸𝐷𝑠 × 81 LEDs
We use a 24-bit color LED strip with 2 wire SPI protocol
Refresh rate

20. Hall Effect Sensor Using Hall Effect Sensor to measure the RPM
Indication of the starting point
Parameter
Output
North Pole
High
Null or weak magnetic field
South Pole
Low
Pin 1 Vin, 2 GND, 3 OUT
With the hall effect sensor we can also determine the exact position each led at while spinning thus we can fix the position to display the image

21. Hardware Achievements
Upload Program wirelessly
Microcontroller coordinates LED display and motor rotation with TIP transistor
Microcontroller transmits data at 8 𝑀𝑏𝑖𝑡𝑠 𝑠𝑒𝑐
Hall Effect sensor monitors the motor rotation speed

22. Hardware Future Improvement
Improve data transmission speed for LED Strip
Chip with higher frequency
LED Strip with multiple data lines
Lunan will further introduce the software system

23. Software Overview Magnet Interrupt LED Strip programming
Two Degree of Freedom(2DOF) Algorithm
User Input Interface

24. Magnet Interrupt
Use Arduino attachInterrupt() to receive signal from Hall Sensor
attachInterrupt(Pin, ISR, Mode);
Pin - Pin number on Arduino. Pin 2 or 3 for Arduino Uno
ISR - Special functions for interrupts
Mode - Defines when the interrupt should be triggered

25. Magnet Interrupt Magnet.ino - example code void setup(){
attachInterrupt(0, h_magnet_detect, FALLING); }
void loop(){}
void h_magnet_detect(){
LED_INDEX = 0;
h_revolutions++;

26. LED Strip Programming FastLED
An Arduino library for programming addressable LED Strips
CRGB color groups
Refresh rate for DotStar APA102 are 24 MHZ. We only achieve 8 MHZ due to hardware limitation.
Data Transmission cannot be interrupted

27. LED Strip Programming fastLED.ino - example code void setup(){
FastLED.addLeds<APA102, Data, Clock, RGB>(leds, NUM_LEDS); }
void loop(){
for(int i = 0; i < NUM_LEDS; i++)
leds[i] = CRGB::Green;
FastLED.show();

28. 2DOF Algorithm Rotation Per Minute(RPM) Calculation Refresh Rate
𝑅𝑃𝑀= 𝑁𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑅𝑜𝑡𝑎𝑡𝑖𝑜𝑛𝑠 𝑇𝑖𝑚𝑒 𝑜𝑓 𝑅𝑜𝑡𝑎𝑡𝑖𝑜𝑛𝑠 × 60 𝑠𝑒𝑐
Refresh Rate
𝑅𝑒𝑓𝑟𝑒𝑠ℎ 𝑅𝑎𝑡𝑒= 1 𝑁𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑃𝑖𝑥𝑒𝑙𝑠 × 𝑅𝑃𝑀
Refresh Rate is related to the FPS requirement. For optimal display, we need to achieve 24 FPS, which is 720 RPM.

29. Pseudocode for 2DOF Algorithm
Set Up:
Set up Magnet Interrupts and LED Strips
Loop:
Calculate RPM and Refresh Rate for vertical/horizontal every five rotations
Check time for update. If yes, disable Interrupts and go to the next step. Other go back to Loop
Update LED properly
Enable Interrupts and go back to Loop

30. Hardware limitations in 2DOF
Data Transmission cannot be interrupted
Interrupt may be blocked during Data Transmission
Inaccuracy for LED Positions
Microcontroller only sends data at 8MHZ
Currently only refreshes LED Strip around 80 times in one rotation at 720 RPM
Our goal is to refresh around 600 times in one rotation at 720 RPM

31. User Input Interface
Allow users to customize display patterns

32. Software Achievements
Calculate RPM for both Horizontal and Vertical Direction
Display graphic patterns for both 1DOF and 2DOF
Display User Input Graphic Pattern

33. Future Software Improvements
Easy user input for UI
Allow users to type words or numbers
Translate them into graphic pattern

34. Results

35. Results

36. Credits David Switzer Vivian Hou Jackson Lenz Braedon Salz Ankit Jain
Professor Kumar
Professor Galvin

37. Questions? Feeback: -Fix block diagram
-Bigger text for some of the slides
-include a video of results
-fix the equation on slide 6 (use equation editor)
-SELL IT! Entertainment. Better ways to market things?