Block diagram of the system:
Figure (D) shows the overall block diagram of “Device control using the telephone” construction.
Circuit description:
This system is divided into two sections, 1: Remote Section 2: Local Control Section.
REMOTE SECTION:
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. 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.
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.
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.
Local Control Section
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.
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.
MT 8870 DTMF decoder:
IC MT8870/KT3170 serves as DTMF decoder. This IC takes DTMF signal coming via telephone line and converts that signal into respective BCD number. It uses same oscillator frequency used in the remote section so same crystal oscillator with frequency of 3.85M Hz is used in this IC.
Working of IC MT8870:
The MT-8870 is a full DTMF Receiver that integrates both band split filter and decoder functions into a single 18-pin DIP. Its filter section uses switched capacitor technology for both the high and low group filters and for dial tone rejection. Its decoder uses digital counting techniques to detect and decode all 16 DTMF tone pairs into a 4-bit code. External component count is minimized by provision of an on-chip differential input amplifier, clock generator, and latched tri-state interface bus. Minimal external components required include a low-cost 3.579545 MHz crystal, a timing resistor, and a timing capacitor. The MT-8870-02 can also inhibit the decoding of fourth column digits.
MT-8870 operating functions include a band split filter that separates the high and low tones of the received pair, and a digital decoder that verifies both the frequency and duration of the received tones before passing the resulting 4-bit code to the output bus.
The low and high group tones are separated by applying the dual-tone signal to the inputs of two 6th order switched capacitor band pass filters with bandwidths that correspond to the bands enclosing the low and high group tones.
The filter also incorporates notches at 350 and 440 Hz, providing excellent dial tone rejection. Each filter output is followed by a single-order switched capacitor section that smoothes the signals prior to limiting. Signal limiting is performed by high gain comparators provided with hysteresis to prevent detection of unwanted low-level signals and noise. The MT-8870 decoder uses a digital counting technique to determine the frequencies of the limited tones and to verify that they correspond to standard DTMF frequencies. When the detector recognizes the simultaneous presence of two valid tones (known as signal condition), it raises the Early Steering flag (ESt). Any subsequent loss of signal condition will cause ESt to fall. Before a decoded tone pair is registered, the receiver checks for valid signal duration (referred to as character- recognition-condition). This check is performed by an external RC time constant driven by ESt. A short delay to allow the output latch to settle, the delayed steering output flag (StD) goes high, signaling that a received tone pair has been registered. The contents of the output latch are made available on the 4-bit output bus by raising the three state control input (OE) to logic high. Inhibit mode is enabled by a logic high input to pin 5 (INH). It inhibits the detection of 1633 Hz.
The output code will remain the same as the previous detected code. On the M- 8870 models, this pin is tied to ground (logic low).
The input arrangement of the MT-8870 provides a differential input operational amplifier as well as a bias source (VREF) to bias the inputs at mid-rail. Provision is made for connection of a feedback resistor to the op-amp output (GS) for gain adjustment.
The internal clock circuit is completed with the addition of a standard 3.579545 MHz crystal.
The input arrangement of the MT-8870 provides a differential input operational amplifier as well as a bias source (VREF) to bias the inputs at mid-rail. Provision is made for connection of a feedback resistor to the op-amp output (GS) for gain adjustment.
The internal clock circuit is completed with the addition of a standard 3.579545 MHz crystal.
hello!
i want the fully detail of this project like circuit diagram, component,discription,blockdiagram,equilanant ICs list that used in this project and coding.
please……
i m very thankful to you…
Great project renjith!!!
pls give circuit diagram device control through telephone. using micro controller IC. IC 89S52
pls i would like see the circuit diagram and implementation of the project
it is too good but i want some more inf
sir,m doin this project but by usin mc-8951…can u mail me details if u hav any?
sir i m an engineering student..
i work on this project in my final sem..
but because of some errors in my program my project is not run..
will u please send me a program..
sir,my submission will be start from 14 april…
so,plz send me a prog. as fast as possible…
plz sir,,,,,
Hy –
i want the fully detail of this project like circuit diagram, component,discription,blockdiagram,equilanant ICs list that used in this project and coding.
please……
i m very thankful to you…
Sir I need the circuit and components urgently I cannot find it anywhere.please help.
Hi,
Doing MSC project and would
highly appreciate if you can send me the fully detail of this project
like circuit diagram, components,description,block diagram,equivalent
ICs list ,microproccesor used.
Kind request
Regards,
Bernard
I have visited your blog before. The more I visit, the more I keep coming back! ;-P
sir,i am doing a project on this
i need a fully detail on this project like circuit diagram, components,description,block diagram,equivalent ICs list that used in this project and coding., used.
hi, i need the coding 4 this project. pls send me the coding(program)……
Smart Idea ranjith !
Me too working on the same concept, can do me a favour? If you can send me its block and Circuit Diagram please.
Thanx,
looking forward for ur positive reply 😉
sir,
very very thanks
i need a fully detail on this project like circuit diagram, components,description,block diagram,equivalent ICs list that used in this project and coding., microcontrller programming for controlling devices
this is agood project.
i need this project.
hi…
how to make code on PIC simulator for automated appliances
controller using PIC16F84A
please answer my question.
how to make code on PIC simulator for automated appliances
controller using PIC16F84A
this is a very important project….i need your answer….
this is really good project please give the detail information and circuit diagram
Sir, please forward me the details of this project like circuit diagram and
further description of this project !
need a fully detail on this project like circuit diagram, components,description,block diagram,equivalent ICs list that used in this project and coding..its humble request
sir,
can u please provide the complete information reguarding this project. Iwould be pleased if u do so…..
sir
i want to know fully detail of ‘dtmf based remote control using telephone ‘project like name and description,equevalent ic’s list that used in this project and coding..its humble request
i am student of ece final year,i need the details of this project for minor project.pls mail me all data of this…
hi ranjith!!!!
really a must appreciable one!!it would create immense pleasure if i could get a clear idea of how u applying the concept..
thanking you!!
bye!!!
Sir,
I want to be a full information about this project,
How to make a circuit and other things which can clear my doubts.
Thank You !
Sir,
I want to be a full information about this project,
How to make a circuit and other things which can clear my doubts.
Thank You
sir i want the circuit diagram of this …. in order to learn it practically
how it works…
i will be very much thankful to u … if u forward me the circuit diagram and
further details on this topic….
hello!
i want the fully detail of this project like circuit diagram, component,discription,blockdiagram,equilanant ICs list that used in this project and coding.
please……
hello
i found the project extremely innovative and interesting..i am wanting to make
it for my college technical festival..it is just a month far from now..if you
could just help me out i would be very grateful..i just need a few tips and the
component list..ilive in india so advice me the appropriate devices..
i am extremely grateful to you..i would appreciate if you could reply as soon as
possible..
thank you
could you please mail me all details including circuit diagram.. i need it
please mail me the program and detail about project
Hi
I am doing a similar project.
Could you please mail me the design details including circuit diagrams
and snapshots(if available) of this project.
It would be of great help.
thanks
Wow….
I am interested to do this project for my home’s devices control so plz send me all details of this project with list all require components, circuit diagram, and details about how to do it…
I hope that you will send me all this detail earlier…
Thank you so much…
i want to make it, so plz send me all detail regarding this project.
I read all about this project and i like it so much, so can u plz send me all the details like circuit diagram, component used ,description and block diagram.Hoping for your reply as early as possible.
Thank you
hi i am using 89c2051 in this project which controls 8 relays and the controlling keys are 11,21—-81 to turn 1-8 relays and 10-80 to turn off.pls send me the program code for this as soon as possible.
sir,
can u send me the project to my mail id ovsureshbabu@gmail.com plz
hi, really very interesting project,please can you send me the full details of it,even every small detail,to work in one shot, my mail is vipinbali2010@gmail.com
thanks
vipin
plz send me all detail regarding this project.