Department of Electrical

1
INKLESS COLOR BLACKBOARD WITH MEMORY
COIL DESIGN
NANOMATERIAL
Each display pixel requires its own magnetic
field. By passing direct current through loops of
magnet wire, one can create an electromagnet to
generate such a field only when powered. Using
the Law of Biot-Savart, one can determine the
field, B, at a particular distance from the loop
of wire z, based on its current I, radius r, and
number of turns N.
This nanomaterial served as the inspiration
behind the project. Given its ability to change
color when exposed to magnetic fields, it
provides an ideal material to use for a
multicolor display with color resolution defined
largely by the preciseness of magnetic field
biasing points. The material itself consists of
"superparamagnetic
colloidal
nanocrystal clusters" of iron oxide that form
"ordered structures when exposed to external
magnetic fields" The diffraction wavelength
(color) of the material can

be altered by modulating the strength of the
applied
magnetic field. A broad
spectrum (red to violet) can be

created by varying the magnetic field strength
from 50
gauss (red) to 500 gauss
(violet), while the material

when not exposed to any magnetic field is brown
in
color.
Department of Electrical Systems Engineering
Group 4
Furthermore, by use of a ferrite core within the
loops of wire, one can scale the field by a
constant factor µrod, based on the
length-to-diameter ratio and the rod materials
characteristics. The values for B, r, z, and I
constrain the design to a particular N but allow
for freedom to choose wire diameter d. A longer
rod allows for a greater µrod but increases the
thickness of the board. Determining the right d
presents a tradeoff between pixel size and
increase in resistance per rod (and thus, power
dissipation). All of these factors must be
considered in design.
AdvisorsDr. Jorge SantiagoDr. Dwight Jaggard
Lisa FlemingRafi HasibEaswaran Subbaraman
Special ThanksPhilip FarnumSid DeliwalaSansern
Somboonsong
ABSTRACT The blackboard continues to remain a
classroom standard, allowing lecturers to
visually communicate information and erase it as
necessary for reusability. As society continues
through the digital age, the convenience of
storing notes electronically has become a more
attractive means for preserving
information. Several products have been
developed that attempt to integrate these two
ideas, often incorporating a mounted projector
with a computer to send and receive information.
However, the implicit requirement of an overhead
projector makes this a very costly alternative to
the traditional blackboard. Furthermore, any
extra embedded features offered, in an effort to
justify cost, detract from the primary purpose of
loading and storing written data. In the chosen
approach, a potentially cost-effective
alternative is explored, making use of
electromagnets within a self-contained device.
Based on the superparamagnetic, luminescent
properties of an iron oxide based nanomaterial,
an array of electromagnetic coils generates
magnetic fields that alter the color of the
compound. The hardware supporting each pixel is
able to accomplish two main goals detecting when
the stylus has passed over a pixel, and then
setting the current through the electromagnet to
produce the correct magnetic field. A
microcontroller, responsible for activating the
coils, also stores the state of the array that
can then be exported to an image file or
redisplayed on the board. The proof-of-concept
prototype that has been developed allows the user
to draw using one of three colors, and erase as
well. The size of the screen is three pixels by
five pixels so that single digit numbers and most
letters can be displayed.
Images of the nanomaterial when exposed
increasing magnetic fields
SYSTEM OVERVIEW
Illustration of the structure of iron oxide
colloids that have self assembled when exposed to
a magnetic field (1)
Prototype coil(3.5 length, 0.125 diameter,
31 AWG wire)
Stylus
Save Color Buttons
Optical microscope images showing the assembly of
CNCs in a film between two glass slides. The
field strength increases from (a to b) (1)
Pixel Hardware

• All quotes and images taken from
• Ge et al. Self-Assembly and Field-Responsive
  Optical Diffractions of Superparamagnetic
  Colloids, American Chemical Society, 02/13/2008

Decoder
Switch
Electromagnet Coil Array
Microcontroller
Differentiator
The hardware, which is identical for each pixel,
was designed to simultaneously detect when the
stylus passes over its respective pixel as well
as to keep the pixels electromagnet generating
the field needed to maintain color on the board.
When the stylus passes over the electromagnet,
the induced current in the coil creates a
voltage spike at the top of the coil with an
amplitude of approximately 30 mV. This node is
the input to a differentiator, which produces a
voltage output proportional to the change of the
input voltage. This voltage spike is amplified
to register as a high input signal to the
microcontroller, as shown in the image on the
right. Once the pixel is detected as active, the
coils color is set. The two bits that the
microcontroller outputs are the control bits for
a decoder. The decoder ensures that out of the
four outputs present (one for each color state),
only one is active at a time.
Image Formatter
Nanomaterial Display
Process Flowchart
ComputerInterface
Computer Display
The microcontroller serves as the central

processing core
for the blackboard,

coordinating detection of stylus
swipes and

the corresponding setting of pixel color, saving

the array
state to memory, and clearing the

board when the
user wishes to do so. The

microcontrollers logic for these basic
tasks is illustrated in the process flowchart
above. Detection of stylus swipes is
interrupt-driven, thus minimizing microprocessor
usage while maximizing the response time to user
input. Each interrupt updates the affected
pixels color by polling the color buttons and
then outputting two bits to the decoder. These
two bits represent what color the pixel should be
set to three colors plus erase. The pixel
hardware then sets the coil voltage to the
appropriate value. Finally the microcontroller
updates its color value in the array that
stores the color values for all of the pixels in
the blackboard.
Image of voltage spike differentiator output
To obtain different voltages for the different
colors, a voltage divider is used. Each voltage
is connected an analog switch, all of whose ends
are shorted together. The control logic for the
switches is the decoder output, which ensures
that two different voltages will not be shorted
together. This voltage is connected to the base
node of a transistor, which isolates the biasing
voltages from the electromagnet. The resulting
current that flows through the electromagnet
produces the correct magnetic field.
The save feature allows a user to save a copy of
the blackboards current state to the
microprocessors memory. These saved images can
then be redisplayed by typing the save position
into the computer after specifying that a load is
desired.
Demo Times Thursday, April 24, 2008 1030 am 12
noon 200 pm 300 pm
Pixel Hardware Circuit Diagram
HC11 Microcontroller Board
PIXEL HARDWARE
MICROCONTROLLER COMPUTER