📄 device control using telephone electrosofts.com.htm
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circuit gives an acknowledgement tone after switching ON the devices to
confirm the status of the device.</font></span></p>
<p style="margin: 5pt 0in 0pt 0.5in; text-indent: -0.25in;" align="justify">
<b><font size="2" face="Verdana">11.</font><span style="font-style: normal; font-family: Verdana; font-variant: normal;"><font size="2">
</font></span><font size="2" face="Verdana">You can control devices from
local telephone. It can also be controlled by PCO.</font></b></p>
<p style="margin-bottom: 0pt;" align="justify">
<font color="#ff0000" size="2">
<span style="font-weight: 700; font-family: Verdana;">Taking a tour of the
project:</span></font></p>
<p style="margin-bottom: 0pt;" align="justify"><b>
<font size="2" face="Verdana"> This system uses Dual Tone Multi
Frequency (DTMF) technology of our telephone set. Every telephone set will
have this facility. We have two type of dialing facilities in our
telephone system (i) Pulse dialing mode (ii) Tone dialing mode. Here this
system works on tone dialing mode. The DTMF mode is shortly called as tone
dialing mode. (Check for availability of tone dialing mode in your
telephone set). </font></b></p>
<p align="justify"><span style="font-weight: 700;">
<font size="2" face="Verdana">This system is divided into two sections 1:
Remote Section 2: Local Control Section.</font></span></p>
<p style="margin-bottom: 0pt;" align="justify">
<font color="#800000" size="2" face="Verdana"><i>
<span style="font-weight: 700;">1: Remote Section:</span></i></font></p>
<p style="margin-bottom: 0pt; text-indent: 0.5in;" align="justify">
<span style="font-weight: 700;"><font size="2" face="Verdana"> It is
nothing but remote telephone set which is present in the remote place.
This may be your workspace (office / school) phone or mobile phone or a
phone in PCO. Signals are sent through this telephone.</font></span></p>
<p style="margin-bottom: 0pt;" align="justify">
<font color="#800000" size="2" face="Verdana"><i>
<span style="font-weight: 700;">2: Local Control Section:</span></i></font></p>
<p style="margin-bottom: 0pt;" align="justify">
<span style="font-weight: 700;"><font size="2" face="Verdana">
This is a control system through which you can control your appliances.
This contains one telephone line and a control unit. The appliances to be
controlled must be connected to telephone line through control unit
.Control unit is kept with a sufficient backup.</font></span></p>
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<p style="margin-bottom: 0pt;" align="center">
</p>
<p style="margin-bottom: 0pt;" align="justify">
<font size="2" face="Verdana"> </font><b><span style="color: rgb(255, 0, 0); font-family: Verdana;"><font size="2">WHAT
IS DTMF?</font></span><font color="#ff0000" size="2"><span style="font-family: Verdana;">
</span></font></b></p>
<p class="MsoNormal" align="justify"><span style="font-weight: 700;">
<font size="2" face="Verdana"> When you press a button in the
telephone set keypad, a connection is made that generates a resultant
signal of two tones at the same time. These two tones are taken from a row
frequency and a column frequency. The resultant frequency signal is called
"<i>Dual Tone Multiple Frequency</i>". These tones are identical and
unique.</font></span></p>
<p class="MsoNormal" align="justify"><font face="Verdana"><b>
<span style="color: purple;"><font size="2"> </font></span>
<span style="color: black;"><font size="2">A </font></span><i>
<span style="color: black;"><font size="2">DTMF</font></span></i><span style="color: black;"><font size="2">
signal is the algebraic sum of two different audio frequencies, and can be
expressed as follows: </font></span></b></font></p>
<p class="MsoNormal" align="center"><font face="Verdana"><b>
<span style="color: black;"><font size="2">f(t) = </font></span><font size="2">A<sub>0</sub><span style="color: black;">sin(2*</span>П<span style="color: black;">*</span>f<sub>a</sub><span style="color: black;">*t)
+ </span>B<sub>0</sub><span style="color: black;">sin(2*</span>П<span style="color: black;">*</span>f<sub>b</sub></font><span style="color: black;"><font size="2">*t)
+ ........... </font></span><span style="color: black;"><font size="2">
------->(1)</font></span></b></font></p>
<p class="MsoNormal" style="text-indent: 0.5in;" align="justify">
<font face="Verdana"><b><span style="color: black;"><font size="2">Where f<sub>a</sub>
and f<sub>b</sub> are two different audio frequencies with A and B as
their peak amplitudes and f as the resultant DTMF signal.</font></span><font size="2">
f<sub>a</sub> <span style="color: black;">belongs to the low frequency
group and </span>f<sub>b</sub></font><span style="color: black;"><font size="2">
belongs to the high frequency group.</font></span></b></font></p>
<p class="MsoNormal" align="justify">
<span style="font-weight: 700; color: black;">
<font size="2" face="Verdana"> Each of the low and high frequency
groups comprise four frequencies from the various keys present on the
telephone keypad; two different frequencies, one from the high frequency
group and another from the low frequency group are used to produce a DTMF
signal to represent the pressed key. </font></span></p>
<p class="MsoNormal" align="justify">
<span style="font-weight: 700; color: black;">
<font size="2" face="Verdana">The amplitudes of the two sine waves should
be such that </font></span></p>
<p class="MsoNormal" align="center">
<span style="font-weight: 700; color: black;">
<font size="2" face="Verdana">
(0.7 < (A/B) <
0.9)V
-------->(2)</font></span></p>
<p class="MsoNormal" align="justify">
<span style="font-weight: 700; color: black;">
<font size="2" face="Verdana"> The frequencies are chosen such
that they are not the harmonics of each other. The frequencies associated
with various keys on the keypad are shown in figure (A).</font></span></p>
<p class="MsoNormal" align="justify"><span style="font-weight: 700;">
<font size="2" face="Verdana"> When you send these DTMF signals
to the telephone exchange through cables, the servers in the telephone
exchange identifies these signals and makes the connection to the person
you are calling. </font></span><font size="2" face="Verdana"> </font></p>
<p class="MsoNormal" align="justify"><span style="font-weight: 700;">
<font size="2" face="Verdana">The row and column frequencies are given
below: </font></span></p>
<p class="MsoNormal" align="center"><font size="2" face="Verdana"> </font><span style="font-weight: 700;"><font size="2" face="Verdana"><img src="Device%20Control%20Using%20Telephone%20%20ElectroSofts.com_files/dtmftable1.jpg" border="0" width="387" height="242"></font></span></p>
<p class="MsoNormal" style="text-align: center;" align="center">
<span style="font-weight: 700;"><font size="2" face="Verdana">Fig (A)</font></span></p>
<p class="MsoNormal" style="text-indent: 0.5in;" align="justify">
<font size="2" face="Verdana"> </font><span style="font-weight: 700;"><font size="2" face="Verdana">When
you press the digit 5 in the keypad it generates a resultant tone signal
which is made up of frequencies 770Hz and 1336Hz. Pressing digit 8 will
produce the tone taken from tones 852Hz and 1336Hz. In both the cases, the
column frequency 1336 Hz is the same. These signals are digital signals
which are symmetrical with the sinusoidal wave. </font></span></p>
<p class="MsoNormal" style="text-indent: 0.5in;" align="justify">
<font size="2" face="Verdana"> </font><span style="font-weight: 700;"><font size="2" face="Verdana">A
Typical frequency is shown in the figure below:</font></span></p>
<p class="MsoNormal" align="center"><font size="2" face="Verdana"> </font><span style="font-weight: 700;"><font size="2" face="Verdana"><img src="Device%20Control%20Using%20Telephone%20%20ElectroSofts.com_files/dtmfsignal.jpg" border="0" width="328" height="210"><br>
Figure (B)</font></span></p>
<p class="MsoNormal" style="text-indent: 0.5in;" align="justify">
<font size="2" face="Verdana"> </font><font face="Verdana"><b><span style="color: black;"><font size="2">Along
with these DTMF generator </font></span><font size="2">in our telephone
set provides a set of special purpose groups of tones, which is normally
not used in our keypad. These tones are identified as 'A', 'B', 'C', 'D'.
These frequencies have the same column frequency but uses row frequencies
given in the table in figure (A). These tones are used for communication
signaling.</font></b></font></p>
<p class="MsoNormal" style="text-indent: 0.5in;" align="justify">
<font size="2" face="Verdana"> </font><span style="font-weight: 700;"><font size="2" face="Verdana">The
frequency table is as follows: </font></span></p>
<p class="MsoNormal" align="center"><font size="2" face="Verdana"> </font><span style="font-weight: 700;"><font size="2" face="Verdana"> <img src="Device%20Control%20Using%20Telephone%20%20ElectroSofts.com_files/dtmftable2.jpg" border="0" width="422" height="242"> <br>
Figure (C)</font></span></p>
<p style="margin-bottom: 0pt;" align="justify">
<span style="font-weight: 700;"><font size="2" face="Verdana"> Due to
its accuracy and uniqueness, these DTMF signals are used in controlling
systems using telephones. By using some DTMF generating IC抯 (UM91214,
UM91214, etc) we can generate DTMF tones without depending on the
telephone set.</font></span></p>
<p style="margin-bottom: 0pt;"><font color="#ff0000" size="2">
<span style="font-weight: 700; font-family: Verdana;">CIRCUIT DESCRIPTION:</span></font></p>
<p style="margin-bottom: 0pt;"><span style="font-weight: 700;">
<font size="2" face="Verdana">This system is divided into two sections, 1:
Remote Section 2: Local Control Section.</font></span></p>
<p style="margin-bottom: 0pt;"><b><font color="#800000" face="Verdana"><u>
<font size="2">REMOTE SECTION</font></u><font size="2">:</font></font></b></p>
<p style="margin-bottom: 0pt;" align="justify"><b>
<font size="2" face="Verdana"> This unit consists of telephone
set which is present in the remote place. This may be your workspace
(office / school) phone or mobile phone or a phone in PCO. Signals are
sent through this telephone. The figure (E) shows the circuit diagram of
the DTMF encoder which resembles the telephone set. It uses DTMF encoder
integrated circuit, Chip UM 91214B<font color="#ff0000">
<a href="http://www.alldatasheet.com/datasheet-pdf/pdf/77334/UMC/UM91214B/datasheet.pdf">
(click here to download datasheet)</a></font>. This IC produces DTMF
signals. It contains four row frequencies & three column frequencies. The
pins of IC 91214 B from 12 to 14 produces high frequency column group and
pins from 15 to 18 produces the low frequency row group. By pressing any
key in the keyboard corresponding DTMF signal is available in its output
pin at pin no.7. For producing the appropriate signals it is necessary
that a crystal oscillator of 3.58MHz is connected across its pins 3 & 4 so
that it makes a part of its internal oscillator.</font></b></p>
<p style="margin-bottom: 0pt; text-align: center;" align="center"><b>
<font size="2" face="Verdana"><img src="Device%20Control%20Using%20Telephone%20%20ElectroSofts.com_files/dtmfencoder.jpg" border="0" width="334" height="321"></font></b></p>
<p style="margin-bottom: 0pt; text-align: center;" align="center">
<span style="font-weight: 700;"><font size="2" face="Verdana">Figure (E).
Circuit diagram of the DTMF encoder</font></span></p>
<p class="MsoNormal" align="justify"><span style="font-weight: 700;">
<font size="2" face="Verdana"> </font></span><b>
<font size="2" face="Verdana"> This encoder IC requires a voltage of 3V.
For that IC is wired around 4.5V battery. And 3V backup Vcc for this IC is
supplied by using 3.2v zener diode.</font></b></p>
<p class="MsoNormal" style="text-indent: 0.5in;" align="justify"><b>
<font size="2" face="Verdana">The row and column frequency of this IC is
as on the fig. "B". By pressing the number 5 in the key pad the output
tone is produced which is the resultant of addition of two frequencies, at
pin no. 13 & pin no.16 of the IC and respective tone which represents
number '5' in key pad is produced at pin no.7 of the IC . This signal is
sent to the local control system through telephone line via exchange.</font></b></p>
<p style="margin-bottom: 0pt;" align="justify"><b>
<font color="#800000" face="Verdana"><u><font size="2">LOCAL CONTROL
SECTION:</font></u><font size="2"> </font></font></b></p>
<p style="margin-bottom: 0pt; text-indent: 0.5in;" align="justify">
<span style="font-weight: 700;"><font size="2" face="Verdana">This is a
control unit through which you can control your appliances. This contains
one telephone line and a Local Control Section. The appliances to be
controlled must be connected to telephone line through control unit.
Control unit is kept with a sufficient backup.</font></span></p>
<p style="margin-bottom: 0pt;" align="justify"><font face="Verdana"><b>
<font size="2">Local Control Section consists of a DTMF decoder, 4-16 line
decoder/demultiplexer, D-flip-flops, and relay driver circuits. Before
going into detail of the circuit, we will take a brief description about
integrated circuits used in local control section.</font><i><font size="2">
</font></i></b></font></p>
<p style="margin-bottom: 0pt;" align="justify">
<font color="#003a85" size="2" face="Verdana"><i>
<span style="font-weight: 700; text-decoration: underline;">MT 8870 DTMF
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