Rs232 laser transceiver

RS-232 Laser Transceiver
Page | 1
Submitted to
Department of Computer Engineering
V.P.M.’s Polytechnic, Thane
2009-2010
Type of project: Interfacing
Submitted by
Noopur Mahesh Koli
Roll No. 33
Under The Supervision Of:
Prof. Mrs. Anita S. Diwakar

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Contents
 Laser …
01
 Why use a laser …
02
 Block diagram and description
… 03
 Circuit diagram
… 04
 Working of circuit …
05
 Regulated power supply …
06
 Interfacing Diagram of
MAX232 IC and Serial Port …
07
 RS232 Serial Port Connector …
08

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 RS232 Standards …
12
 Components Used …
13
 Construction …
 Software ...
 Testing …
 Future and Applications …
 Bibliography …
LASER
Light Amplification by Stimulated Emission of Radiation
(LASER or laser) is a mechanism for emitting electromagnetic
radiation, typically light or visible light, via the process of
stimulated emission.

Page | 4
The emitted laser light is usually a spatially coherent, narrow low-
divergence beam, which can be manipulated with lenses. In laser
technology, "coherent light" denotes a light source that emits light
of in-step waves of identical frequency and phase. The laser’s
beam of coherent light differentiates it from light sources that emit
incoherent light beams, of random phase varying with time and
position; whereas the laser light is a narrow-wavelength
electromagnetic spectrum monochromatic light; yet, there are
lasers that emit a broad spectrum light, or simultaneously, at
different wavelengths.
Why Use A Laser?
 A laser as a communications medium has some unique
properties compared to other forms of media.
 A line-of-sight laser beam is useful where wires cannot be
physically connected to a remote location.

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 A laser beam, unlike wires, also does not require special
shielding over longer distances.
 Lasers offer at least an order of magnitude longer distances
compared to infrared LEDs.
 Although RF transmitters may offer longer distances than
line-of-sight lasers, they are subject to interference from
other transmitters.
 Since the laser medium is line-of-sight and the beam being
only several millimeters in diameter it is very difficult for the
data stream to be tapped. This offers secure communication
since any attempts to intercept the laser beam would be
detected at the receiver as a loss in data.
 A laser medium also allows for the sender and receiver to be
galvanically isolated from each other.
Precaution: Never look directly into the laser beam as eye damage
may occur.

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Description
The block diagram above shows the communication of two PC’s
using laser as the transmission media, and the RS232 port as the
medium of interface.
PC1 sends the data through RS232 port to the laser transceiver,
which in turn, sends the data to the second transceiver, and through
the RS232 port to PC2.
In a transceiver, the action of sending, as well as receiving the data
can be done, though not simultaneously.
Block Diagram
PC1 PC2

Page | 7

Page | 8
Working of Circuit
 The transceiver is based on the MAX232A IC for
generating and receiving RS-232 compatible voltage
signals.
 The receiving sensor is an LDR. It minimizes ambient
light interference.
 The signal from the LDR is buffered via a pair of Schmitt
trigger buffers to clean up and square the signal.
 The output of the second buffer is then directly converted
to a RS-232 standard signal via the MAX232 IC.
 The MAX232 IC generates +10V and -10V voltage
swings using a dual charge-pump voltage converter from a
single +5VDC rail.
 The laser diode driver consists of a 7405 open-collector
hex inverter IC. All the outputs of the inverters are
coupled together to provide enough drive current for the
laser diode which draws around 35mA @ 3V.
 A 7805 voltage regulator is used to provide the IC and
laser diode with a stable 5V voltage source.
 The two 1N4001 diodes, in series with the laser diode,
step down the voltage from +5VDC to around 3.6VDC
which is close to the nominal voltage for the laser diode.
 The transceiver is designed in such a way that when no
signal is present the laser is on. This helps you see where
the laser is pointing during the laser-detector alignment.
 The transceiver is powered by the same regulated power
supply and draws approximately 80mA (laser on) and
40mA (laser off).

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Regulated Power Supply
 The +5 volt power supply is based on the commercial 7805
voltage regulator IC.
 This IC contains all the circuitry needed to accept any input
voltage from 8 to 18 volts and produce a steady +5 volt
output, accurate to within 5% (0.25 volt).
 It also contains current-limiting circuitry and thermal
overload protection, so that the IC won't be damaged in case
of excessive load current; it will reduce its output voltage
instead.
 The 1000µf capacitor serves as a "reservoir" which maintains
a reasonable input voltage to the 7805 throughout the entire
cycle of the ac line voltage.
 The two rectifier diodes keep recharging the reservoir
capacitor on alternate half-cycles of the line voltage, and the
capacitor is quite capable of sustaining any reasonable load in
between charging pulses.
 The 100µf capacitor serves to help keep the power supply
output voltage constant when load conditions change.

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Interfacing Diagram of MAX232 IC and Serial Port
Connector

Page | 11
COMPONENTS LIST
Component Value Description Cost
R1 1k 1/4 W resistor Re.1/-
C1-5 0.1uF Capacitor (Ceramic) Re.1/-
U1 MAX232A RS-232 line driver Rs.15/-
U2 74LS05 Hex open-collector buffer Rs.15/-
U3 74LS14 Schmitt trigger hex inverter Rs.15/-
D1-2 1N4001 Power diode Re.1/-
P1 - Light Dependent Resistor Rs.15/-
V1 7805 Voltage regulator Rs.10/-
L1 LX1000 Laser Pointer Rs.35/-
. . 9V battery clip Rs.20/-
. . DB-9 female connector with
back shell.
Rs.12/-
. . 2 m shielded 3 core cables. Rs.8/-
. . Switch Rs.8/-
. . PCB Rs.30/-
. . Light duty hook-up wire Rs.60/-

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MAX 232A IC
 Since RS232 standard was set long before the advent of TTL
logic family, its input & output voltages are not TTL
compatible.
 In RS232, 1 is represented by -3 to -25volts while a 0 bit is
+3 to +25 volts, making -3 to +3 undefined.
 For this reason to connect any RS232 port to a device, we
must use voltage converters such as MAX232.
 This IC receives the signal from the LDR and sends it to the
port and receives signal from port and send it to laser
transmitter.

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Pin No. Pin Name Pin Description
1 C1+ + Connector for capacitor C1
2 VS+ Output of voltage pump
3 C1- - Connector for capacitor C1
4 C2+ + Connector for capacitor C2
5 C2- - Connector for capacitor C2
6 VS- Output of voltage pump/inverter
7 T2out Driver 2 output
8 R2in Receiver 2 input
9 R2out Receiver 2 output
10 T2in Driver 2 input
11 T1in Driver 1 input
12 R1out Receiver 1 output
13 R1in Receiver 1 input
14 T1out Driver 1 output
15 GND Ground
16 VCC Power Supply

Page | 14
Serial Port Connector
RS232 Female Connector RS232 Male Connector

Page | 15
Pin
No.
Abbreviation Pin Name Pin Description
1 DCD Data Carrier
Detect
Tells DTE that DCE is
connected to telephone
line (optional).
2 RxD Receive Data Carries data from DCE to
DTE.
3 TxD Transmit Data Carries data from DTE to
DCE.
4 DTR Data Terminal
Ready
Tells DCE that DTE is
ready to be connected
(optional).
5 GND Ground Common Ground
6 DSR Data Set Ready Tells DTE that DCE is
ready to receive
commands or data.
7 RTS Request To
Send
Tells DCE to prepare to
accept data from DTE.
8 CTS Clear To Send Acknowledges RTS and
allows DTE to transmit.
9 RI Ring Indicator Tells DTE that DCE has
detected a ring signal on
the telephone line.

Page | 16
RS-232 Standards
 RS-232 is a standard for transferring data in serial format.
 Information is sent in small packets of data called data
frames.
 A data frame consists of the following sequence: a start bit,
the actual data word, an optional parity bit and ends with one
or two stop bits.
 The data word can be 7 or 8 bits long. RS-232 offers
asynchronous communication with the combination of start
and stop bits of being used to synchronize each data frame.
 The parity bit is used by the receiver to determine if an odd
number of bits were corrupted during transmission.
 There are two types of parity, odd and even.
 For example, if even parity is used the transmitter makes the
parity bit a 1 anytime there is an odd number of 1’s in the
data word.
 This makes a total even number of bits in the data frame.
 If an odd number of bits arrive at the receiver then the data
frame was corrupted.
 The standard not only specifies the order of bits but also
specifies the voltage levels used to send the data.
 Bipolar signaling is used in the RS-232 protocol to support
long cabling with minimum noise.
 A logic 0 is represented by a positive voltage between
+3VDC and +15VDC and a logic 1 is represented by a
negative voltage between -3VDC and -15VDC.
 The IBM PC serial port contains a number of handshaking
lines that are used to indicate the willingness of the receiver
to receive data and the sender to send data.

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Schmitt trigger(IC 74LS14)
Schmitt trigger converts any type of waveforms such as sine,
triangular to square wave. So it is a square wave converter.
Once a threshold at the input is exceeded it turns on or goes high.
Below the threshold it turns off, or goes low.
Hex Inverter Open Collector(IC 74LS05)
The laser diode driver consists of a 7405 open-collector hex
inverter IC. All the outputs of the inverters are coupled together to
provide enough drive current for the laser diode which draws
around 35mA @ 3V.

Page | 18
Phototransistor
Like diodes, all transistors are light-sensitive. Phototransistors are
designed specifically to take advantage of this fact. The most-
common variant is an NPN bipolar transistor with an exposed base
region. Here, light striking the base replaces what would ordinarily
be voltage applied to the base -- so, a phototransistor amplifies
variations in the light striking it. Note that phototransistors may or
may not have a base lead (if they do, the base lead allows you to
bias the phototransistor's light response.
For phototransistor selection and comparison information, see the
phototransistor section of the BEAM Reference Library's BEAM
Pieces collection.
Note that photodiodes also can provide a similar function, although
with much lower gain (i.e., photodiodes allow much less current to
flow than do phototransistors). You can use this diagram to help
you see the difference (both circuits are equivalent):

Page | 19
Microsoft Visual Basic
VISUAL BASIC is a high level programming language which was
evolved from the earlier DOS version called BASIC. BASIC
means Beginners' All-purpose Symbolic Instruction Code. It is a
very easy programming language to learn. The codes look a lot like
English Language. Different software companies produced
different version of BASIC, such as Microsoft QBASIC,
QUICKBASIC, GWBASIC, and IBM BASICA and so on.
However, it seems people only use Microsoft Visual Basic today,
as it is a well developed programming language and supporting
resources are available everywhere. Now, there are many versions
of VB exist in the market, the most popular one and still widely
used by many VB programmers is none other than Visual Basic 6.
We also have VB.net, VB2005 and the latest VB2008 and VB2010
which is a fully object oriented programming (OOP) language. It is
more powerful than VB6 but looks more complicated to master.
Advantages provided by the Microsoft Visual Basic:
 It is user friendly
 It provides us with graphical user interface
 It is easy to interface hardware using this software
 It also provides inbuilt components which makes the
working easy

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Dimp, s, u1, u2, p1, p2, q1, q2, a1, a2, s1, s2 As String
Private SubCommand1_Click()
If List1.ListIndex =-1 ThenMsgBox ("Please SelectUserName")
Else
If List1.ListIndex =0 Then
Open"C:Aadmin.txt"ForInputAs#1
Line Input#1, s
Line Input#1, p
Close #1
If Text1.Text= p Then

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Form2.Show
Else
MsgBox ("Incorrectpassword")
End If
End If
Open"C:Auser1.txt"ForInputAs#1
Line Input#1, s
Line Input#1, p
Close #1
Form2.Show
Else
End If
End If
Open"C:Auser2.txt"ForInputAs#1
Line Input#1, s
Line Input#1, p
Close #1
Form2.Show

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Else
End If
End If
End If
End Sub
Private SubCommand2_Click()
End
End Sub

Page | 23
Dim user As String
Private Sub Command1_Click()
Form10.MSComm1.Settings = "9600,N,8,1"
Form10.MSComm1.CommPort = 1
Form10.MSComm1.InputLen = 1
Form10.MSComm1.PortOpen = True
Form10.MSComm1.RThreshold = 1
Form10.Show
Unload Me ‘ unload currently active form
End Sub
If Form1.List1.ListIndex = 0 Then
Form3.Show
End If
Form4.Show
End If
Form4.Show
End If
Unload Me
End Sub

Page | 24
End
End Sub
Form1.Text1.Text = ""
Form1.Show
Unload Me
End Sub

Page | 25
Form1.Show
Unload Me
End Sub
Form2.Show
Unload Me
End Sub
Private Sub Option1_Click(Index As Integer)
Form5.Show
Unload Me
End Sub
Private Sub Option2_Click()
Form6.Show
Unload Me
End Sub
Form7.Show
Unload Me
End Sub

Page | 26
Form8.Show
Unload Me
End Sub
Form1.Show
Unload Me
End Sub

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Form2.Show
Unload Me
End Sub
Private Sub Option1_Click(Index As Integer)
Form5.Show
Unload Me
End Sub
Form6.Show
Unload Me
End Sub

Page | 28
Dim u, p, q, a, t, s As String
Form1.Show
Unload Me
End Sub
Open "C:Aadmin.txt" For Input As #1

Page | 29
Line Input #1, u
Line Input #1, p
Line Input #1, q
Line Input #1, a
Close #1
If Text1.Text = p And Text2.Text = Text3.Text Then
t = Text2.Text
Open "C:Aadmin.txt" For Output As #1
Print #1, u
Print #1, t
Print #1, q
Print #1, a
Close #1
MsgBox ("Your password has been changed successfully")
Form2.Show
Unload Me
Else
MsgBox ("wrong message")
End If
End If
Open "C:Auser1.txt" For Input As #1
Line Input #1, u
Line Input #1, p
Line Input #1, q

Page | 30
Line Input #1, a
Line Input #1, s
Close #1
t = Text2.Text
Open "C:Auser1.txt" For Output As #1
Print #1, u
Print #1, t
Print #1, q
Print #1, a
Print #1, s
Close #1
Form2.Show
Unload Me
Else
End If
End If
Line Input #1, u
Line Input #1, p
Line Input #1, q
Line Input #1, a

Page | 31
Line Input #1, s
Close #1
t = Text2.Text
Print #1, u
Print #1, t
Print #1, q
Print #1, a
Print #1, s
Close #1
Form2.Show
Unload Me
Else
End If
End If
End Sub
Form2.Show
Unload Me
End Sub

Page | 32
Dim u, p, q, a, q1, a1, s As String
Form1.Show
Unload Me
End Sub

Page | 33
Line Input #1, u
Line Input #1, p
Line Input #1, q
Line Input #1, a
Close #1
If Text1.Text = p Then
q1 = Text2.Text
a1 = Text3.Text
Open "C:Aadmin.txt" For Output As #1
Print #1, u
Print #1, p
Print #1, q1
Print #1, a1
Close #1
MsgBox ("Your security question has been changed successfully")
Form2.Show
Unload Me
Else
End If
End If
Line Input #1, u
Line Input #1, p

Page | 34
Line Input #1, q
Line Input #1, a
Line Input #1, s
Close #1
q1 = Text2.Text
a1 = Text3.Text
Print #1, u
Print #1, p
Print #1, q1
Print #1, a1
Print #1, s
Close #1
Form2.Show
Unload Me
Else
End If
End If
Line Input #1, u
Line Input #1, p

Page | 35
Line Input #1, q
Line Input #1, a
Line Input #1, s
Close #1
q1 = Text2.Text
a1 = Text3.Text
Print #1, u
Print #1, p
Print #1, q1
Print #1, a1
Print #1, s
Close #1
Form2.Show
Unload Me
Else
End If
End If
End Sub
Form2.Show

Page | 36
Unload Me
End Sub
Dim u, p, q, a, b, c, d, e, s, s1, s2, b2, c2, d2, e2 As String
Form1.Show
Unload Me
End Sub
If s1 = "0" Then
s = "1"

Page | 37
If Text1.Text = " " Then
MsgBox ("Enter username")
End If
If Text4.Text = " " And Text5.Text = " " Then
MsgBox ("You must enter security question and it's answer")
End If
If Text2.Text = Text3.Text Then
u = Text1.Text
p = Text2.Text
q = Text4.Text
a = Text5.Text
Print #1, u
Print #1, p
Print #1, q
Print #1, a
Print #1, s
Close #1
MsgBox ("Your account has been created successfully")
Form2.Show
Unload Me
Else
MsgBox ("The two passwords do not match.")

Page | 38
End If
ElseIf s1 = "1" And s2 = 0 Then
s = "1"
If Text1.Text = " " Then
MsgBox ("Enter username")
End If
If Text4.Text = " " And Text5.Text = " " Then
MsgBox ("You must enter security question and it's answer")
End If
If Text2.Text = Text3.Text Then
u = Text1.Text
p = Text2.Text
q = Text4.Text
a = Text5.Text
Print #1, u
Print #1, p
Print #1, q
Print #1, a
Print #1, s
Close #1
MsgBox ("Your account has been created successfully")

Page | 39
Form2.Show
Unload Me
Else
MsgBox ("The two passwords do not match.")
End If
ElseIf s1 = "0" And s2 = "0" Then
MsgBox ("you have already created 2 users")
End If
End Sub
Form2.Show
Unload Me
End Sub
Private Sub Form_Load()
Line Input #1, b
Line Input #1, c
Line Input #1, d
Line Input #1, e
Line Input #1, s1
Close #1

Page | 40
Line Input #1, b2
Line Input #1, c2
Line Input #1, d2
Line Input #1, e2
Line Input #1, s2
Close #1
End Sub
Dim u, u1, u2, s, s1, s2, p1, p2, p3, q1, q2, a1, a2 As String
Unload Form1
Unload Me

Page | 41
Load Form1
Form1.Show
End Sub
If Text1.Text = p3 Then
If List1.ListIndex = -1 Then
MsgBox ("Please Select User Name")
ElseIf List1.Text = u1 Then
s = "0"
Print #1, u1
Print #1, p1
Print #1, q1
Print #1, a1
Print #1, s
Close #1
MsgBox ("Your account has been deleted successfully")
Form2.Show
Unload Me
ElseIf List1.Text = u2 Then
s = "0"
Print #1, u2
Print #1, p2

Page | 42
Print #1, q2
Print #1, a2
Print #1, s
Close #1
MsgBox ("Your account has been deleted successfully")
Form2.Show
Unload Me
End If
Else
MsgBox ("Enter correct Password")
End If
End Sub
Form2.Show
Unload Me
End Sub
Line Input #1, u
Line Input #1, p3
Close #1

Page | 43
Line Input #1, u1
Line Input #1, p1
Line Input #1, q1
Line Input #1, a1
Line Input #1, s1
Close #1
Line Input #1, u2
Line Input #1, p2
Line Input #1, q2
Line Input #1, a2
Line Input #1, s2
Close #1
With List1
If s1 = "1" Then
.AddItem u1
End If
If s2 = "1" Then
.AddItem u2
End If

Page | 44
If s1 = "0" And s2 = "0" Then
MsgBox ("You haven't createt users yet. Press OK to create new account.")
Form3.Show
Unload Me
End If
End With
End Sub

Page | 45
Dim u, p, q, a As String
Form1.Show
Unload Me
End Sub
If Text1.Text = a Then
Form2.Show
Unload Me
End If
End Sub
End
End Sub
Line Input #1, u
Line Input #1, p
Line Input #1, q
Line Input #1, a

Page | 46
Close #1
Label2.Caption = q
Text2.Text = u
ElseIf Form1.List1.ListIndex = 1 Then
Line Input #1, u
Line Input #1, p
Line Input #1, q
Line Input #1, a
Close #1
Label2.Caption = q
Text2.Text = u
Else
Line Input #1, u
Line Input #1, p
Line Input #1, q
Line Input #1, a
Close #1
Label2.Caption = q
Text2.Text = u
End If
End Sub

Page | 47
Dim s, v As String
If MSComm1.CommPort = 1 Then
If MSComm1.PortOpen = False Then
MSComm1.PortOpen = True
MsgBox "port open"
End If
Else
MsgBox ("port error")
End If

Page | 48
s = Text1.Text
MSComm1.Output = s
MSComm1.OutBufferCount = 0
End Sub
End
End Sub
Unload Form1
Unload Me
Load Form1
Form1.Show
End Sub
Form2.Show
End Sub
Private Sub MSComm1_OnComm()
Text2.Text = MSComm1.Input
MSComm1.InBufferCount = 0
End Sub

Page | 49

Page | 50
Advantages
 Low cost
 Resistance to interference
 Privacy of communication
 In many countries freedom from legislative control
Disadvantages
 A line of sight path is required
 Transceivers need stable mounting and careful alignment
 Adverse weather can disrupt communication
 Birds may interrupt the laser beam, so error correcting
protocols are necessary unless occasional errors are tolerable.

Page | 51
Further Advancements
 Faster modulation speeds can be achieved when using a laser
module which is designed to be modulated.
 There are some semiconductor laser modules which have
modulation option built into the laser module (separate wire
for modulation signal).
 Those laser modules are much more expensive than those
cheap laser pointer laser modules.

Page | 52
References
Books:
Jan Axelson. (2000). Serial Port Complete. Madison, USA:
Lakeview Research Publication.
Steven Holzner. (2009). Visual Basic 6 Programming Black Book.
Delhi: Brijbasi art press.
Web Sites:
www.google.co.in
www.electronics-lab.com/projects/pc/002/
www.howstuffworks.com

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