Matt Baxter, Elias Desalegn, Dikshit Katam, Zakir Mohamed, Bryan Skarke, Michael Morrison

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DIGITAL BRAILLE DEVICE
Matt Baxter, Elias Desalegn, Dikshit Katam,
Zakir Mohamed, Bryan Skarke, Michael Morrison
mmb053000_at_utdallas.edu, erd061000_at_utdallas.edu,
dxk072100_at_utdallas.edu, zhm041000_at_utdallas.edu,
bcs051000_at_utdallas.edu, mrm045000_at_utdallas.edu
Department of Electrical Engineering Erik Jonsson
School of Engineering Computer
Science University of Texas at Dallas Richardson,
Texas 75083-0688, U.S.A.
PROJECT GOALS
POWER AND CONTROL

• To design an easily readable device that
  dynamically displays Braille characters.
• Develop an alternative Braille pin actuation
  method that is lower cost than current options.
• Potential Impact
• Most current Braille display devices rely on
  piezoelectric materials for pin actuation. This
  has made them extremely expensive and out of
  reach for many potential consumers. A cheaper
  alternative could mean greater accessibility, and
  easier implementation into many applications (ex
  public displays like ATMs or information kiosks).

Pulse Width Modulation (PWM) The circuit shown
below takes a DC voltage input and outputs a
pulse width modulated signal. This PWM signal is
a square wave with an adjustable duty cycle. In
our project, we chose to use PWM to easily adjust
the drive speed of our pin motors. By connecting
the PWM signal to the gate of a transistor, you
can drive power through a motor in pulses. If
the pulse width is decreased, the motor will run
at a slower speed because the effective voltage
over a period of time is less. The effective
voltage can be expressed as Duty Cycle()
Amplitude(V). H-Bridge Applying a
positive voltage across a motor will drive it in
one direction only. To effectively apply the
voltage in the opposite terminal configuration, a
circuit concept known as an H-Bridge will be
used. The most basic H-Bridge consists of four
switching transistors 2 pull-up and 2
pull-down. If you short the middle of this
bridge with the motor and turn on opposite
corners of the bridge, a current will be driven
through the motor. Likewise, if you turn on the
alternate corners the current will be driven in
the other direction. Thus, by supplying the
proper logic inputs we can control the motors
direction. For our project, we have chosen the
TI SN754410 (quad half-h drivers) which can be
configured as two full H-Bridges
BRAILLE PIN DESIGN
PWM Circuit (NE555 Timer IC)
PWM Signal on Oscilloscope
We considered three different Braille pin
designs vibrating Braille dots utilizing
vibrating motors, electromagnetic linear
actuators, and linear actuator motors. The
vibrating Braille dots were ruled out because
discerning a vibrating dot from a neighbor in
such a small space would have been difficult.
The vibrating motors were the same type used in
cell phones and pagers, and although they were
very small they would have been very difficult to
isolate from one another. Next, we started to
experiment with creating electromagnetic driven
linear actuators. We built numerous pin
prototypes based on the principal of repelling a
permanent magnet upward by energizing an
electromagnet at the base. One major problem we
faced was holding the Braille pin in its UP state
without constantly powering the electromagnet.
One attempt at solving this problem involved the
creative use of the clicker end of a ball-point
pen (as a mechanical model) to catch and release
the pin as it was bumped by the actuator.
Although this method worked and the
electromagnetic actuator seemed viable, in the
end it was deemed unrealistic due to power
consumption and mechanical complexity.
Our final design choice involved
linear actuator motors. Since miniature
actuators are very costly, we built our own using
inexpensive components pager motors, screws,
coupling nuts, and some flexible metal straps.
The screw is attached directly to the motor drive
shaft such that it spins when the motor spins.
The coupling nut rides up/down depending on the
spin direction. The flexible metal straps were
added for stability and to ensure that the nut
would not rotate with the shaft/screw. Some of
the advantages of using these linear actuator
motors include simple construction, low power
consumption, and the ability to hold the pin in
the up/down position without the need to keep the
actuator energized (unlike the electromagnet
concept).
H-Bridge Example
TI SN754410
PROJECT CONCLUSIONS/OUTCOMES

• We created a single large-scale Braille cell
  using custom-built linear actuator motors.
• Suitable motor speeds and direction control
  designed using a Pulse Width Modulated signal
  generator and an H-Bridge.

Electromagnetic Actuator Design
Linear Actuator Motor Design
FUTURE GOALS

• Implement microcontroller for message handling,
  encoding, and pin control.
• Minimize and scale mechanical parts to more
  closely represent scale of Braille dots.
• Fully implement a small multi-character device
  capable of dynamically displaying full words in
  Braille.