Full Color Hi Res POV Display - MS&T Senior Design

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A photo of the POV next to the control board.

This page describes progress on Robert Givens and my Senior Design Project here at Missouri S&T. Our project of choice was a Persistence of Vision (POV) display. However, to make it innovative, we decided to make ours particularly high resolution and most importantly with full color capability. Our current goal is 256 (8bit) colors. This project encompasses the fields of Microcontrollers, FPGAs, Inductive Power, Optics and high speed circuit design. These individual elements are broken down in detail below.

Contents

POV Testing

Here are a few pictures of what we have gotten working so far.

Picture2.jpg POV1.jpg IMAGE1.JPG

POV Design

Rotor

A rendering of the POV Rotor assembly

The rotor is made up of multiple PCB's which are held together with hardware and spun to draw the image in the air. The rotor is made up of three PCB's. The front most PCB which we call the "LED Board" contains the LED's and electronics to drive the LED's. The next PCB which is located in the middle is called the "FPGA Board". The "FPGA Board" contains an FPGA which decodes the signal and sends the data to the LED board to be displayed. The last board in the rotor stack is called the "Power Board" this board contains the power circuitry to rectify the AC power from the inductive transfer and it also contains the high speed photo diode circuitry.

A photo of the laser cut mock assembly for motor testing

This is a mock up of the rotor which we created using Robert's Laser Cutter. This mock up allowed us to test the new motor design to make sure it was capable of spinning the POV up to the required speed.

This is a photo of the assembled rotor

Here is a picture of the assembled rotor PCB's.

LED Board


A rendering of the "LED Board"
A photo of the "LED Board"

The LED Board is just that it is the board that contains the LED's and the led drivers/shift registers.

Board Dimensions

Parts

PCB Layout

This is the schematic for the LED Board

This is (rather obviously) the display Printed Circuit Board for our POV assembly. This board consists of 48 surface mount RGB LEDs mounted at precise spacing. This board was the most difficult due to the precise position, size and number of components. This PCB is a 2-layer (traces and components) standard FR4 PCB with 8mil minimum spacing and trace size. Layout was done in Mentor PADS after aborting with Eagle. Without basic push/shove routing and enforced design rules it was nearly impossible to make progress without having to go back and delete 15 traces because the 16th was 0.01mm too close to the edge.

This is the PCB layout of the LED Board which was created using Mentor Graphics Pads

FPGA Board


A rendering of the "FPGA Board"

The FPGA Board...

Board Dimensions

Parts

Power Board


A rendering of the "Power Board"

The Power Board...

Optical Transfer Ring

A rendering of the optical transfer ring assembly

In order to transfer data to the rotor in real time we had to find a method to transfer it wirelessly because the rotor is spinning. We decided to transfer the data optically because of the high data rates that would need to be achieved to allow at least 24 fps of streaming video. The optical transfer assembly uses two circular channels one for the clock and one for the data. The base of the assembly is a PCB which has the rings of high speed IR LEDS mounted to it.

One layer of rings for the optical transfer ring assembly

Attached on top of that pcb are three layers of rings. Each layer consists of three rings which allow us to separate the clock and the data signals. The ring layers are cut from 6mm black acrylic using a laser cutter. The rings are then mounted to the PCB using 18 #0-80 screws.

A set of the rings cut using Robert's laser cutter

We cut a set of the rings (shown on the right) to make sure that it was possible to cut them accurately. After a little tweaking we got then to cut with of tolerance of +/- 0.5mm which is good enough for our design.

Inductive Power Transfer

A rendering of POV base with the ferrite cores attached to the drive shaft
A photo of the POV base with motor and pot cores attached
A rendering of POV base with the fixed ferrite core visible

Motor and Base

A rendering of the POV base with the attached motor and driveshaft
A rendering of the POV base with the shaft coupler and flange bearing

Motor and Driver

Base

A photo of the laser cut interlocking stand base
A photo of the laser cut interlocking stand base in the locked position

Software

So far two applications have been developed to make this project possible. Read more about them by clicking on the images below:

Screenshot 2.png POVSync Screenshot.png

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