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fiercebunElectronics - Devices

Nov 2, 2013 (3 years and 8 months ago)

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Team: Recursively Awesome

Circuit Design a
nd Theory of Operation


1

I.

Introduction



The AccuroCam is a camera mounted on a platform that has the ability to pan
360° a
nd tilt approximately 90°. The p
latform
has two modes of operation and will be

controlled
either wirelessly through

a cell phone

or through a key
pad device
. The user
can either
enter

in a number and the camera will pan or tilt through the specified degrees
or the user can go to continuous control mode where one has the ability to start and stop
the movement whenever needed. A text to speech convert
er will provide feedback to the
user regarding the status of the platform. The web
cam mounted on the platform will run

a
web

server that can be accessed to view the scene under surveillance by the camera.



In order for the micro controller to deco
de instructions from the cell phone, a DTMF
(Dual Tone Multiple Frequency) decoder will be used that indicates which button on the
cell phone
or keypad
has been pressed. Once the micro controller has received a
command, it will initiate the stepper motor a
ction in the appropriate direction and amount
via a PWM and a shift register implemented via a PLD. The microcontroller will also
send information to the text to speech chip so that feedback is a
vailable to the user. A
potentiometer

will send back informat
ion to the microcontroller regarding the position of
the
motors
. The microcontroller will then account for any discrepancies. This part is
extremely critical because one of the main attractions of the
AccuroCam

is its accuracy.












Team: Recursively Awesome

Circuit Design a
nd Theory of Operation


2

II.
Theory of Op
eration


A.
Power Circuit

The AccuroCam will be

powered directly by 120VAC.

A wall
-
w
art will be used
to

convert the AC voltage to 12V DC. This DC voltage will be used to power the

analog
circuitry of the camera platform, specifically the stepper motor

driv
er and the speaker.
The 12VDC powe
r supply will be fed through a MAX5035
DC

to DC converter chip to
create a 5V power supply for the digital circuitry.

The analog and the digital circuits will
be physically separated on the

board and tied to a common groun
d at one point. The
associated circuitry for

the power supply is the circuitry recommended by the chip
manufacturer.


B.
Motor Circuit

The step
per motors will be driven by 4 IRL530

transistors

each
.
The stepper
motors

are four phase unipolar

motors
. Two w
ires (red, green) are tied to +12V and each
of the four phases is connected directly to the drain side

of a transistor. The source side of
the transistor is connected to ground

and the gate is connected to the switching signal.
The phase excitation

sequenc
e for the motors is black, yellow, brown
, orange

for
a
single

clockwise

step. The

switching s
ignals for the transistors come

from t
wo

PALCE16V8
PLDs (
one

PLD for each motor
)
. The PLDs are configure
d to act as stepper drive chips.

A

PWM signal and a directi
on signal are input to each PLD from the

microcontroller.
The output of the PLD feeds each transistor and turns the

transistors on an
d off according
to the correct stepping sequence for a given direction.


C.
Micro
controller Circuit


The microcontroller wi
ll provide the PWM and direction

signals for the motor
circuit.

There will be seven in
puts into the microcontroller.
These inputs include two
analog potentiometer readings which will feed into two A/D channels and five inputs
fr
om the PLD of the DTMF circu
it.

Of the five inputs from the PLD, one will be an
interrupt to notify the microcontroller that a key has been pressed and the remaining four
will be data bits represent
ing which key has been pressed.

Corresponding motor outputs
will be changed according
to the inputs r
eceived.
The microcontroller will provide the
Team: Recursively Awesome

Circuit Design a
nd Theory of Operation


3

standby signa
l for the text to speech chip.
There will be an external reset switch for the
microcontroller.

The operating frequency of the microcontroller is 4 Mhz. Since the
calculations in the
microcontroller are not computationally intensive, there are no
operating frequency constraints here. The focus of the motor control is accuracy, not
speed; therefore, there are no operating frequency constraints here either.



D.
User Interface

circuit


The
User Interface

circuit enables the user to use either the ke
ypad or a cell phone
for input.

The keypad sig
nal will be sent through a keypad

en
coder which will the
n send
the information to the
PLD.
The DTMF chip is used to convert the cell phone button
presses into digital outputs which are fed into the PLD also. There will be an external
switch to indicate whether the keypad or the cell phone will be used to control the
motors.
If the switch is closed then the
keypad inputs are used. Conversely, if the
switch
is open then the cell phone inputs are used. The output of the PLD will then be fed into
the microcontroller.



E.
T
ext to
S
peech Circuit



The text to speech
encoder is interfaced to the microcontroller via the Serial
Communications Interface on th
e microcontroller. ASCII data is sent to the text to speech
encoder at a baud rate of 2400 bps, a reliable baud rate specified by the manufacturer of
the text to speech encoder [
10
]. A “null” character transmi
tted
over the serial interface
signals the end
of transmission and initiates the text to speech encoding. It is possible for
the character buffer in the text to speech encoder to become full and prevent any further
data transmission. To recover from the above situation the microcontroller also has the
capability to “hard” reset the text to speech encoder.







Team: Recursively Awesome

Circuit Design a
nd Theory of Operation


4


III. ORCAD Schematic

See attached document.


IV. ORCAD Design Rule Check Report

See attached document.


V. ORCAD Bill of Materials Report

See attached document.






























Team: Recursively Awesome

Circuit Design a
nd Theory of Operation


5

V
I
.

List of References


[1]


DTMF Receiver Datasheet”, [Online Document], 2005 September,

Available HTTP:
http://www.calmicro.com/products/data/pdf/cm8870.pdf


[2]
“MAX5035 DC
-
DC Converter Datasheet”, [Online Document], 2005 September,

Available HTTP: http:/
/www.maxim
-
ic.com/quick_view2.cfm/qv_pk/3991


[3]

“Danaher Stepper Motor Datasheet”
, [Online Document], 2005 September, Available
HTTP:
http://shay.ecn.purdue.edu/~477grp7/documents/motor_data.pdf


[4] “
Text to Speech V
-
Stamp Datasheet
”, [Online Document],

2005 September,

Available HTTP:

http://www.rcsys.com/dnlds.htm#docs


[5] “
PALCE16V8 Family Datasheet
”, [Online Document], 2005 September,

Available HTTP:
http://shay.ecn.purdue.edu/~dsml/ece270/Refs/Pld/palce16v8.pdf


[6] “
9S12C Module Connections
”, [Onli
ne Document], 2005 September,

Available HTTP:

http://shay.ecn.purdue.edu/~dsml/ece362/MiniPrj/module_connections.pdf


[7] “
Non
-
Inverting Amplifier Circuit
”, [Online Document], 2005 September,

Available HTTP:

http://hyperphysics.phy
-
astr.gsu.edu/hbase/elect
ronic/opampvar.html#c3


[8] “
Low Pass Filter Design
”, [Online Document], 2005 September,

Available HTTP:

http://www.st
-
andrews.ac.uk/~www_pa/Scots_Guide/experiment/lowpass/lpf.html


[9] “
IRL530 Transistor Datasheet
”, [Online Document], 2005 September,

Avai
lable HTTP:

http://www.fairchildsemi.com/pf/IR/IRL530A.html


[10] “RC8650 2 Wire Serial Interface App. Note”, [Online Document], 2005 September,
Available HTTP:
http://www.rcsys.com/Downloads/an24.pdf