Difference between revisions of "Persistence-of-Vision Display"

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== Team Members ==
== Overview ==
[[image:POV|right]]
[[image:POV|right]]
A fully customizable display using the concept of Persistence of Vision was created as a final project for ME333 in 2009. User-specified images (and even moving images) were displayed by rotating a column of LEDs at speeds faster than 300rpm. Each individual LED was modeled as a row of pixels. Conversely, the rotational position of the panel of LEDs represented the pixel columns of the display; the time interval and rotational speed determined the width of the pixel columns.
* Gregory McGlynn(Computer Science, Class of 2011) [left]

=== Team Members ===
* Gregory McGlynn (Computer Science, Class of 2011) [left]
* Kwang Xiong Sim (Mechanical Engineering, Class of 2010) [center]
* Kwang Xiong Sim (Mechanical Engineering, Class of 2010) [center]
* Alexander Park (Material Science, Class of 2009) [right]
* Alexander Park (Material Science and Engineering, Class of 2009) [right]
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=== Theory of Persistence of Vision ===
== Overview ==
Although arguably much more complex, human vision functions in a manner similar to modern motion pictures; our eyes retain images for a fraction of a second, not unlike a frame in a movie. This is called persistence of vision (POV). When images change fast enough, what we see is a subtle blend of what we see now and a fraction of a second ago.
A fully customizable display using the concept of Persistence of Vision was created as a final project for ME333 in 2009. User-specified images (and even moving images) were displayed by rotating a column of LEDs at speeds faster than 300rpm. Each individual LED was modeled as a row of pixels. Conversely, the rotational position of the panel of LEDs represented the pixel columns of the display; the time interval and rotational speed determined the width of the pixel columns.
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== Theory of Persistence of Vision ==
Although arguably much more complex, human vision functions in a manner similar to modern motion pictures; our eyes retain images for a fraction of a second, not unlike a frame in a movie. This is called the persistence of vision (POV). When images change fast enough, what we see is a subtle blend of what we see now and a fraction of a second ago.


== Implementation ==
== Implementation ==
[[image:POVschematic|center]]
[[image:POVschematic|thumb|right|250px|Schematic of POV Display]]
In order to avoid the complication of wiring a spinning object, all of the major components of the POV display were placed on a platform mounted on the output shaft of a [[Actuators Available in the Mechatronics Lab#6W Maxon motor with 6:1 gearhead and 100 line encoder|6W Maxon motor]]. The components of this rotating platform include a [[PIC Microcontroller]], a panel of 14 bright white LEDs, a [[Hall Effect Sensor|Hall switch]], an [[XBee radio communication between PICs|XBee radio]], and a battery pack to power the assembly. The strip of LEDs was mounted vertically (or parallel to the axis of rotation) at one end of the platform. To minimize wobbling of the assembly while spinning, the components were positioned such that the center of gravity of the panel passed through the axis of rotation.


Wireless communication between two PICs via [[XBee radio communication between PICs|XBees]] was used to enable live updating of the display based on user input: one PIC (the "display" PIC) was used to control the POV display and receive wireless information from a second PIC. This second "controller" PIC was used to receive user input and transmit it to the display PIC.


We mounted a platform atop the output shaft of a motor. In order to avoid the complication of wiring a spinning object, all of the major components of the POV display are built on this platform, including a PIC microcontroller, a strip of LEDs, and a battery pack to power the assembly. The strip of LEDs will be mounted vertically at an extended end of the platform. In order to stabilize the spinning motion, the components are positioned so that the center of gravity of the panel passes through the axis of rotation.


=== Modes of Operation ===
The POV display has two modes of operation, corresponding to two different input methods.


In the first mode of operation, the controller PIC transmits previously stored data to the PIC on the rotor panel. By varying the resistance of a [[Potentiometers|potentiometer]] on the control panel, the user can choose between eleven "canned" messages.
We made use of wireless communication between two PICs to implement live updating of the display based on user input. One PIC will be used to control the POV display and receive wireless information from a second PIC. The second PIC will receive user input store user input and transmit the data wirelessly to the POV’s PIC.


In the second mode of operation, the controller PIC is connected to a computer via [[PIC RS232#FTDIChip TTL-232R USB to RS232 Cable|USB]]. Using a Java program written by Gregory McGlynn, the user can draw pictures or type letters in real time on the computer screen and on the POV display.


=== Position Sensing ===
The POV display has two modes of operation. In mode 1, the PIC on the control panel transmits data that we had previously stored in it to the PIC on the rotor panel. By varying the resistance of a potentiometer on the control panel, we allow the user to choose between ten pre-stored messages.
To allow for accurate portrayal of the desired image, a [[Hall Effect Sensor|Hall switch]] was utilized to implement position sensing. The Hall switch was mounted near the end of the rotor display platform and a magnet was attached on the top of the base box. The magnet was positioned directly under the path of the hall sensor such that each rotation of the platform triggered an electrical pulse. The display PIC was programmed to reset the image cycle each time a pulse was sensed from the Hall sensor. This allowed reproduction of a stationary image.


Using this implementation of the Hall switch, the display POV was programmed to calculate the rotational velocity of the POV after each rotation by timing the interval between pulses from the Hall switch. This allows for correction of pixel column spacing, such that the column width is consistent even at different speeds. As such, the display may function properly without any information from the motor about its speed.

In mode 2 of operation, the PIC on the control panel is connected to a computer via a USB port. Using a Java program that we wrote, we allow the user to draw pictures or type letters which will get updated real time on the POV display.


In order to ensure accurate portrayal of the desired image, we used a hall sensor to implement position sensing. We wired in a hall sensor towards the end of the rotor display panel and attached a magnet on the top of the base box. The magnet was positioned on the orbiting path of the hall sensor so that it registers a signal everytime it spins a round. We have programmed the display to reset the image cycle everytime the hall sensor was triggered so that the image stays at the same location.
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== Mechanical Design ==
== Mechanical Design ==
=== Base ===
[[image:POV_CADdrawing|center]]
[[image:POV_CADdrawing|right|thumb|250px|CAD representation of POV Display]]
<br clear="all">
The base box was fabricated using black expanded PVC. There are three rectangular faces (the back, top, and bottom), two trapezoidal sides and a door that is hinged at the base such that it opens outwards. The control panel was mounted on the inner face of the door.


A wooden base was mounted to the bottom of this PVC box both to increase the box's integrity and to add to stability of the system with additional mass. A slot was cut near the back of the wooden panel to hold motor in place.
=== Base Box ===
As seen in the above drawing, the base box is built out of rigid expanded PVC. There are 3 rectangle faces, 2 trapezium faces and a door that is hinged at the base so that it opens outwards. The control panel is mounted on the inner face of the door.

An addition wooden base is mounted to the base to increase rigidity of base-to-wall connections and also to weight down the whole setup and make it more stable. A slot is cut towards the back to stick in the motor.

A aluminum coupler is attached to the motor shaft which comes out of the top of the box through a radial bearing. The radial bearing can reduce the degree of freedom of the spinning shaft so it only spins in the vertical axis. It may also be used to support the weight of the rotating display panel of that the whole weight does not rest on the motor shaft. The end of the coupler is milled to a strip that locks in to a complementary hole in the rotating display panel.


The motor output shaft was connected to the POV display platform through an aluminum coupler. This coupler extended out the top of the box through a [[Bearings|radial ball bearing]], which served to reduce lateral motion of the display platform and to support some of the weight of the platform. The end of the coupler was machined to fit snugly in to a slot-shaped hole in the display platform.


<Br><Br>
=== Control Panel ===
=== Control Panel ===
[[image:Picture of Control Panel|right|thumb|250px|Picture of Control Panel]]
Several knobs, buttons, and switches were placed on a control panel to allow for user input: 1) Motor power switch, 2) Motor speed knob, 3) Selection knob for stored responses, 4) Selection button for stored response, 5) Message position knob, and 6) Scroll speed knob. These components were mounted on a piece of expanded PVC through appropriately sized holes. Specifics on the implementation of these components are described below in the Electronic Design section.


<Br><Br><Br><Br><Br><Br><Br>
There are switches that we need to put on the control panel.
=== Rotating Display Platform ===
1) Turns motor on/off
[[image:Picture of Display Platform|right|thumb|250px|Picture of Display Platform]]
2) Control motor speed
Because the display platform rotates rapidly during operation, all of the components were mounted rigidly onto two sheets of expanded PVC. These two sheets were screwed together at the center of the platform, such that a double layer of material was created at the slot for the motor coupler. At one end of the platform, the panel of 14 vertically mounted LEDs was mounted. The electronics of the platform (consisting of a solder board and a PIC board separated by standoffs) were mounted behind the LED panel. A 6V battery pack (4AA's) was mounted at the opposite end of the platform with Velcro. This non-permanent positioning of the battery pack was chosen so that the batteries could be easily replaced and such that the batteries could act as an adjustable counterbalance for the entire platform.
3) Choose stored response
4) Invoke stored response
5) Scroll the message
6) Set scroll speed for message


<Br><Br><Br><Br>
The first control was a simple toggle switch wired between the two motor leads. The second control is a potentiometer wired between the motor, by turning the potentiometer to increase resistance, we can lower the motor speed.
=== Parts List ===
* (1) Radial ball bearing
* Expanded PVC sheet
* Wood (approx. 6" x 5" x 0.5")
* Sheet metal screws
* Various nuts and bolts
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== Electrical Design ==
The third control is implemented by a potentiometer with ten different markings, each corresponding to a stored message. We set the control panel PIC code to recognize ten different intervals of resistance controlled by the potentiometer. After the resistance is set on control 3, pressing button 4 will ask the PIC to grab this resistance value and display the right stored response.
=== Display PIC Electronics ===
[[Image:POVschematicsmall.jpg|thumb|right|Rotating display circuit (click for high-resolution version)]]
The rotating display platform has 14 LEDs which were controlled through Ports C and D of a PIC. Because bright LEDs were used, the amount of current need could not be supplied directly from the output ports of the PIC. As such, the LEDs were wired through two Darlington arrays (DS2003). These ICs consist of 7 [[Diodes and Transistors#Darlington Pair|Darlington pairs]] with a common emitter. The outputs of the PIC were connected to the bases of the transistors; when the PIC drives one of the bases high, current can flow through the transistor and the corresponding LED lights up. We did not find it necessary to use any resistors in this design.


The display uses a [[Hall Effect Sensor|Hall switch]] to synchronize its display with its rotation, as described above. The implemented circuit, as shown schematically at the right, causes pin B0 of the PIC to go low whenever the hall switch is near the magnet mounted on the base box; when the PIC detects this falling edge on pin B0 it knows its relative position. By timing the interval between two of these events the PIC calculates how fast the display is rotating and adjusts its timing accordingly.
Control 5 and 6 are both implemented by potentiometers. Control 5 allows users to scroll the message manually and control 6 allows the user to set the speed at which the message scrolls around.


The display receives commands from the controller PIC via an [[XBee radio communication between PICs|XBee]] radio module.


=== Rotating Display Panel ===


=== Controller PIC Electronics ===
== Electrical Design ==
[[Image:AP_KS_GM=Control_panel_schematic.jpg|thumb|right|Control panel circuit (click for high-resolution version)]]
When using the first [[Persistence-of-Vision Display#Modes of Operation|mode of operation]], the control panel receives user input through three 1000-Ohm potentiometers and a push button. The states of these controls are read by the PIC which uses its XBee radio module to send appropriate commands to the display.


If the USB cable is plugged in, the second mode of operation takes effect and the controller PIC is also responsible for accepting commands from the PC and relaying them to the display PIC through the XBee.
=== Primary Components ===


<Br><Br><Br><Br><Br><Br><Br>
=== Rotating Display Circuit ===
=== Motor Control Electronics ===
[[Image:POVschematicsmall.jpg|400px|right|Display circuit]]
The motor and its electronics were wired separately from the rest of the electronics. A toggle switch was wired in series with a variable resistor (a 25-Ohm potentiometer) between the motor and a 24V power supply. This allowed for the toggle switch to be used as a simple on/off power switch, and the potentiometer to be used to tune the voltage across the motor, effectively varying its speed.
The rotating display has 14 LEDs which are controlled by a PIC. The LEDs are bright and require a good deal of current, which cannot be supplied directly from the output ports of the PIC. Therefore the LEDs are controlled through two Darlington arrays (DS2003). These ICs consist of 7 Darlington pair transistors with a common emitter. The outputs of the PIC are connected to the bases of the transistors. Thus when the PIC drives one of the bases high, current can flow through the transistor and the corresponding LED lights up. We did not find it necessary to use any resistors in this design.


=== Parts list ===
The display uses a [[Hall Effect Sensor]] to synchronize its display with its rotation. The circuit as shown causes pin B0 on the PIC to go low whenever the hall sensor is near a magnet. A magnet is mounted at a fixed location under the display so that when the PIC detects this falling edge on pin B0 it knows that it is positioned above the magnet. By timing the interval between two of these events the PIC calculates how fast the display is rotating and adjusts its timing accordingly.
* (2) PIC18F4520 microcontrollers

* (1) XBee Radio pair and their [[XBee Interface Board|interface boards]]
The display receives commands via an [[XBee radio communication between PICs|XBee]] radio module.
* (2) Darlington Pair Arrays (DS2003)
* (1) Hall switch
* (14) Bright white LEDs
* (3) 1000-Ohm potentiometers
* (1) Push-button
* (1) [[Actuators Available in the Mechatronics Lab#6W Maxon motor with 6:1 gearhead and 100 line encoder|6W Maxon Motor]]
* (1) Toggle Switch
* (1) 25-Ohm Potentiometer
* Solder Board
* Stranded wire
* 10-wire stranded ribbon cable.
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=== Control Panel Circuit ===
[[Image:AP_KS_GM=Control_panel_schematic.jpg|400px|right|Control panel circuit]]


The control panel receives user input through three potentiometers and a pushbutton. The states of these controls are read by the PIC which uses its XBee radio module to send appropriate commands to the display.

If the USB cable is plugged in, the control panel is also responsible for accepting commands from the PC and relaying these commands to the POV through the XBee.
<br clear="all">
== Code ==
== Code ==


Line 92: Line 107:
== Results ==
== Results ==
=== Mode 1: Canned Response ===
=== Mode 1: Canned Response ===
In the first mode of operation, a user can just plug in the POV display into a wall socket, turn on the device and display an image immediately. This will allow a quick and easy demonstration without a computer. We have stored ten different responses on the PIC ROM sitting on the rotating display panel. Using a potentiometer, the device allow the user to set which canned response is being displayed.
In the first mode of operation, the user can just plug in the POV display into a wall socket, turn on the display PIC's power, and turn on the motor to display an image. This allows for a quick and easy demonstration without a computer. We have stored eleven different responses on the display PIC's ROM. Using a knob and a button on the control panel, the user can set which canned response is displayed.


http://www.youtube.com/watch?v=zx5eXrf9oQI[http://www.youtube.com/watch?v=zx5eXrf9oQI]
video link to mode 1


=== Mode 2: Real time image input ===
=== Mode 2: Real time image input ===
In the second mode of operation, a user can interact more closely with the POV display. In this mode, the POV display is connected via a USB port to a computer which needs to have Java installed. The Java program with the code listed above allows a user to draw pictures or type letters which will be tranmitted real time from the control panel PIC to the rotating display panel PIC through the wireless Xbee chips.
In the second mode of operation, a user can interact more closely with the POV display. In this mode, the POV display is connected via a USB port to a computer which needs to have Java installed. The Java program with the code listed above allows users to draw pictures or type letters which will be transmitted in real time from the controller PIC to the display PIC through the wireless XBee chips.


In both modes of operation, we have set up knobs that will allow a user to scroll a message manually or set the scroll speed of an image.
In both modes of operation, we have set up knobs that will allow a user to scroll a message manually or set the scroll speed of an image.


http://www.youtube.com/watch?v=urz729AbkG4[http://www.youtube.com/watch?v=urz729AbkG4]
video link to mode 2


== Additional Notes ==
== Additional Notes ==
=== How to use the POV Display (a brief user's manual) ===

'''Basic Operation'''

In its most basic mode of operation, the display is quite simple to use:
*Plug the power cord into the wall.
*Turn on the battery pack on the rotating display platform.
*Unfold the control panel, and flip the power switch.
The display should spin up and the text "ME333 - Mechatronics" should be displayed. Try out the control panel knobs!


'''Connecting to a Computer'''

It's also possible to draw your own images for the display in real time using the PC software. Note that the program will on run on ''Windows'' machines.


Installing the software:
*Download [[POV-PC.zip]] and save it in its own directory somewhere on your computer.
*Unzip POV-PC.zip with WinZip or some other unzipping tool.
*This will extract 3 files. The important one is POVController.exe. Running this will start the control program. You can run POVController.exe by navigating to the folder it's in with Windows Explorer and double-clicking on the icon.


Starting up POVController.exe:
*Plug the USB cable into the computer before running POVController.exe
*Find out the COM port number of the POV device: in Windows Device Manager, look under "Ports (COM & LPT)" and you should see "USB Serial Port (COM#)," where # represents the appropriate COM port number.
*Run POVController.exe and provide it with the COM port number when prompted and press enter.


Using POVController.exe:
*After starting up POVController.exe as described above, the graphical user interface will appear.
*Click "Clear" to clear the POV display and start with a blank image.
*You can draw on the grid with your mouse to make images appear on the display.
*Selecting the "Erase" check box allows you to use the mouse to erase individual pixels.
*Typing in the applet will make text appear in the GUI.
*If the drawing or text doesn't show up you on the POV display, click the refresh button once. Avoid pressing the refresh button many times consecutively; refreshing takes several seconds and multiple clicks will cause the program to briefly become unresponsive.


'''Troubleshooting'''

''"I don't see any lights!"'' - Did you turn on the battery pack on the display?

''"When I type none of my letters appear in the interface!"'' - Try pressing backspace several times.

''"None of the controls work!"'' - Try turning off the motor, letting the display spin down, and then pushing the reset buttons on both PICs. Sometimes the communication between the two PICs gets misaligned and the PICs have to be reset.


=== Possible Future Improvements/Enhancements ===
=== Possible Future Improvements/Enhancements ===
We have thought about using RGB LEDS to give the display panel more colorful. Also, we can use different sensors to make the display more interactive. For example putting on distance sensors on the display so that the panel color scheme changes when you wave a hand in front of it.
The use of PICs in this project allows for a great number of possibilities for improvement to the display. For instance, different sensors could be mounted to the display platform or added to the controller PIC to make the display more interactive; proximity sensors, microphones, or even touch screens could be added to create more modes of operation. Additionally, using RGB LEDS could allow for a more colorful user experience with the POV display.

Latest revision as of 00:09, 20 March 2009

Overview

POV

A fully customizable display using the concept of Persistence of Vision was created as a final project for ME333 in 2009. User-specified images (and even moving images) were displayed by rotating a column of LEDs at speeds faster than 300rpm. Each individual LED was modeled as a row of pixels. Conversely, the rotational position of the panel of LEDs represented the pixel columns of the display; the time interval and rotational speed determined the width of the pixel columns.

Team Members

  • Gregory McGlynn (Computer Science, Class of 2011) [left]
  • Kwang Xiong Sim (Mechanical Engineering, Class of 2010) [center]
  • Alexander Park (Material Science and Engineering, Class of 2009) [right]

Theory of Persistence of Vision

Although arguably much more complex, human vision functions in a manner similar to modern motion pictures; our eyes retain images for a fraction of a second, not unlike a frame in a movie. This is called persistence of vision (POV). When images change fast enough, what we see is a subtle blend of what we see now and a fraction of a second ago.


Implementation

Schematic of POV Display

In order to avoid the complication of wiring a spinning object, all of the major components of the POV display were placed on a platform mounted on the output shaft of a 6W Maxon motor. The components of this rotating platform include a PIC Microcontroller, a panel of 14 bright white LEDs, a Hall switch, an XBee radio, and a battery pack to power the assembly. The strip of LEDs was mounted vertically (or parallel to the axis of rotation) at one end of the platform. To minimize wobbling of the assembly while spinning, the components were positioned such that the center of gravity of the panel passed through the axis of rotation.

Wireless communication between two PICs via XBees was used to enable live updating of the display based on user input: one PIC (the "display" PIC) was used to control the POV display and receive wireless information from a second PIC. This second "controller" PIC was used to receive user input and transmit it to the display PIC.


Modes of Operation

The POV display has two modes of operation, corresponding to two different input methods.

In the first mode of operation, the controller PIC transmits previously stored data to the PIC on the rotor panel. By varying the resistance of a potentiometer on the control panel, the user can choose between eleven "canned" messages.

In the second mode of operation, the controller PIC is connected to a computer via USB. Using a Java program written by Gregory McGlynn, the user can draw pictures or type letters in real time on the computer screen and on the POV display.

Position Sensing

To allow for accurate portrayal of the desired image, a Hall switch was utilized to implement position sensing. The Hall switch was mounted near the end of the rotor display platform and a magnet was attached on the top of the base box. The magnet was positioned directly under the path of the hall sensor such that each rotation of the platform triggered an electrical pulse. The display PIC was programmed to reset the image cycle each time a pulse was sensed from the Hall sensor. This allowed reproduction of a stationary image.

Using this implementation of the Hall switch, the display POV was programmed to calculate the rotational velocity of the POV after each rotation by timing the interval between pulses from the Hall switch. This allows for correction of pixel column spacing, such that the column width is consistent even at different speeds. As such, the display may function properly without any information from the motor about its speed.

Mechanical Design

Base

CAD representation of POV Display

The base box was fabricated using black expanded PVC. There are three rectangular faces (the back, top, and bottom), two trapezoidal sides and a door that is hinged at the base such that it opens outwards. The control panel was mounted on the inner face of the door.

A wooden base was mounted to the bottom of this PVC box both to increase the box's integrity and to add to stability of the system with additional mass. A slot was cut near the back of the wooden panel to hold motor in place.

The motor output shaft was connected to the POV display platform through an aluminum coupler. This coupler extended out the top of the box through a radial ball bearing, which served to reduce lateral motion of the display platform and to support some of the weight of the platform. The end of the coupler was machined to fit snugly in to a slot-shaped hole in the display platform.



Control Panel

Picture of Control Panel

Several knobs, buttons, and switches were placed on a control panel to allow for user input: 1) Motor power switch, 2) Motor speed knob, 3) Selection knob for stored responses, 4) Selection button for stored response, 5) Message position knob, and 6) Scroll speed knob. These components were mounted on a piece of expanded PVC through appropriately sized holes. Specifics on the implementation of these components are described below in the Electronic Design section.








Rotating Display Platform

Picture of Display Platform

Because the display platform rotates rapidly during operation, all of the components were mounted rigidly onto two sheets of expanded PVC. These two sheets were screwed together at the center of the platform, such that a double layer of material was created at the slot for the motor coupler. At one end of the platform, the panel of 14 vertically mounted LEDs was mounted. The electronics of the platform (consisting of a solder board and a PIC board separated by standoffs) were mounted behind the LED panel. A 6V battery pack (4AA's) was mounted at the opposite end of the platform with Velcro. This non-permanent positioning of the battery pack was chosen so that the batteries could be easily replaced and such that the batteries could act as an adjustable counterbalance for the entire platform.





Parts List

  • (1) Radial ball bearing
  • Expanded PVC sheet
  • Wood (approx. 6" x 5" x 0.5")
  • Sheet metal screws
  • Various nuts and bolts


Electrical Design

Display PIC Electronics

Rotating display circuit (click for high-resolution version)

The rotating display platform has 14 LEDs which were controlled through Ports C and D of a PIC. Because bright LEDs were used, the amount of current need could not be supplied directly from the output ports of the PIC. As such, the LEDs were wired through two Darlington arrays (DS2003). These ICs consist of 7 Darlington pairs with a common emitter. The outputs of the PIC were connected to the bases of the transistors; when the PIC drives one of the bases high, current can flow through the transistor and the corresponding LED lights up. We did not find it necessary to use any resistors in this design.

The display uses a Hall switch to synchronize its display with its rotation, as described above. The implemented circuit, as shown schematically at the right, causes pin B0 of the PIC to go low whenever the hall switch is near the magnet mounted on the base box; when the PIC detects this falling edge on pin B0 it knows its relative position. By timing the interval between two of these events the PIC calculates how fast the display is rotating and adjusts its timing accordingly.

The display receives commands from the controller PIC via an XBee radio module.


Controller PIC Electronics

Control panel circuit (click for high-resolution version)

When using the first mode of operation, the control panel receives user input through three 1000-Ohm potentiometers and a push button. The states of these controls are read by the PIC which uses its XBee radio module to send appropriate commands to the display.

If the USB cable is plugged in, the second mode of operation takes effect and the controller PIC is also responsible for accepting commands from the PC and relaying them to the display PIC through the XBee.








Motor Control Electronics

The motor and its electronics were wired separately from the rest of the electronics. A toggle switch was wired in series with a variable resistor (a 25-Ohm potentiometer) between the motor and a 24V power supply. This allowed for the toggle switch to be used as a simple on/off power switch, and the potentiometer to be used to tune the voltage across the motor, effectively varying its speed.

Parts list

  • (2) PIC18F4520 microcontrollers
  • (1) XBee Radio pair and their interface boards
  • (2) Darlington Pair Arrays (DS2003)
  • (1) Hall switch
  • (14) Bright white LEDs
  • (3) 1000-Ohm potentiometers
  • (1) Push-button
  • (1) 6W Maxon Motor
  • (1) Toggle Switch
  • (1) 25-Ohm Potentiometer
  • Solder Board
  • Stranded wire
  • 10-wire stranded ribbon cable.


Code

Code for the control panel PIC

Code for the display PIC

Code for the PC applet

Results

Mode 1: Canned Response

In the first mode of operation, the user can just plug in the POV display into a wall socket, turn on the display PIC's power, and turn on the motor to display an image. This allows for a quick and easy demonstration without a computer. We have stored eleven different responses on the display PIC's ROM. Using a knob and a button on the control panel, the user can set which canned response is displayed.

http://www.youtube.com/watch?v=zx5eXrf9oQI[1]

Mode 2: Real time image input

In the second mode of operation, a user can interact more closely with the POV display. In this mode, the POV display is connected via a USB port to a computer which needs to have Java installed. The Java program with the code listed above allows users to draw pictures or type letters which will be transmitted in real time from the controller PIC to the display PIC through the wireless XBee chips.

In both modes of operation, we have set up knobs that will allow a user to scroll a message manually or set the scroll speed of an image.

http://www.youtube.com/watch?v=urz729AbkG4[2]

Additional Notes

How to use the POV Display (a brief user's manual)

Basic Operation

In its most basic mode of operation, the display is quite simple to use:

  • Plug the power cord into the wall.
  • Turn on the battery pack on the rotating display platform.
  • Unfold the control panel, and flip the power switch.

The display should spin up and the text "ME333 - Mechatronics" should be displayed. Try out the control panel knobs!


Connecting to a Computer

It's also possible to draw your own images for the display in real time using the PC software. Note that the program will on run on Windows machines.


Installing the software:

  • Download POV-PC.zip and save it in its own directory somewhere on your computer.
  • Unzip POV-PC.zip with WinZip or some other unzipping tool.
  • This will extract 3 files. The important one is POVController.exe. Running this will start the control program. You can run POVController.exe by navigating to the folder it's in with Windows Explorer and double-clicking on the icon.


Starting up POVController.exe:

  • Plug the USB cable into the computer before running POVController.exe
  • Find out the COM port number of the POV device: in Windows Device Manager, look under "Ports (COM & LPT)" and you should see "USB Serial Port (COM#)," where # represents the appropriate COM port number.
  • Run POVController.exe and provide it with the COM port number when prompted and press enter.


Using POVController.exe:

  • After starting up POVController.exe as described above, the graphical user interface will appear.
  • Click "Clear" to clear the POV display and start with a blank image.
  • You can draw on the grid with your mouse to make images appear on the display.
  • Selecting the "Erase" check box allows you to use the mouse to erase individual pixels.
  • Typing in the applet will make text appear in the GUI.
  • If the drawing or text doesn't show up you on the POV display, click the refresh button once. Avoid pressing the refresh button many times consecutively; refreshing takes several seconds and multiple clicks will cause the program to briefly become unresponsive.


Troubleshooting

"I don't see any lights!" - Did you turn on the battery pack on the display?

"When I type none of my letters appear in the interface!" - Try pressing backspace several times.

"None of the controls work!" - Try turning off the motor, letting the display spin down, and then pushing the reset buttons on both PICs. Sometimes the communication between the two PICs gets misaligned and the PICs have to be reset.


Possible Future Improvements/Enhancements

The use of PICs in this project allows for a great number of possibilities for improvement to the display. For instance, different sensors could be mounted to the display platform or added to the controller PIC to make the display more interactive; proximity sensors, microphones, or even touch screens could be added to create more modes of operation. Additionally, using RGB LEDS could allow for a more colorful user experience with the POV display.

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