Device control using Telephone
by Ranjith | November 5th, 2008.Block diagram of the system:
Figure (D). 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.
Figure (E). Circuit diagram of the DTMF encoder
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.
Figure (F).Block diagram of IC MT8870
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.
December 17th, 2008 at 5:17 pm
Very good concept. I will try to do this project.
December 17th, 2008 at 5:18 pm
Thank you!
December 18th, 2008 at 4:17 am
hi
this is very good project
thank
December 19th, 2008 at 3:18 pm
iam very much intrested in this project. i want to know mudh more abt this project
December 23rd, 2008 at 5:43 pm
hi
please explain to me about PCO and DPDT
thank
December 30th, 2008 at 12:22 pm
please send me the coding of “Device control using telephone
January 4th, 2009 at 2:05 pm
PLEASE INFORM A CIRCUIT FOR CELL PHONE – DTMF CONTROLLING DEVICES.
January 4th, 2009 at 2:09 pm
REQUEST TO TO SEND ME A CIRCUIT TO WHICH I CAN ATTACH MY GSM/CDMA CELL PHONE TO THE CONTROL UNIT AND AND MAKE CALLS FROM ANY PHONE AND SEND DTMF TONES TO CONTROL 4 OR 8 SWICHES.
January 12th, 2009 at 11:20 pm
i wanna know how i resemble the encoder circuit throgh my remote telephone
January 17th, 2009 at 11:18 am
please send me the coding of thi project or i want to learn how to do this !! i am very much intresten in ur project ! pleae help !!
thnx n regard !
ujjwal kohli
January 28th, 2009 at 6:04 pm
please send me complete info regarding digital ic tester &it is good to do as final year project in b.e. send more project info also.
February 1st, 2009 at 5:43 am
sir have u got any projects on Cell phone controlled devices
March 3rd, 2009 at 6:30 pm
sir i want to know more about this project ,is it work properly?plssss answer …
March 28th, 2009 at 3:48 pm
hi
this is very good project.
i will use this concept in my project.
April 2nd, 2009 at 3:09 pm
please can u tell me how the values of R5 C5 and R6 C6 are to be given because i am right now assembling the circuit but i dont know how to address these values
July 28th, 2009 at 4:02 pm
hello! i watn the fully detali of this project like circuit diagram, componont,discription,blockdiagram.please send me in soft copy in my mail.
July 31st, 2009 at 6:50 pm
can I try this project for ME level?
August 3rd, 2009 at 1:01 pm
hi,i am very much interested in the project of controlling switch using telephone.please send me the detail information.Thank you
August 5th, 2009 at 8:18 pm
hai frnd
u r doing ME ,this project is not suited 4 me level projects,try in embedded systems or in matlab field,if u want more about this project pls mail to ajith_mgkumar@rediffmail.com
August 12th, 2009 at 12:41 am
hello sir/madam
incredible idea. but please send detail circuit diagram and implementation technique, as i want it to submit as my final year project.
looking forward for the response.
August 19th, 2009 at 1:19 am
hello!
i want the fully detali of this project like circuit diagram, componont,discription,blockdiagram.please send me in soft copy in my mail.
plzzz…
i m very thankful to you…
August 21st, 2009 at 10:02 am
is there any law that it violate? because you are trying to connect something in the telephone line… reply asap…
August 26th, 2009 at 12:52 pm
plz give some more projects
August 26th, 2009 at 1:14 pm
i want know that in this project if i want to use a cellphone insted of a telephone how will it work and also how it will connect
send me more detail about this project it’s such a nice concept withou microcontroller
THANKS
September 1st, 2009 at 11:51 am
Hi, I am using KT3170 as the Decoder. Please enlighten me on how do i connect the telephone line to KT3170?
Also can you explain more on this paragraph “A parallel connection from the telephone line is taken and connected it to telephone interfacing circuit using a DPDT switch. When you wish this section is to be work then you switch ON the DPDT switch otherwise your telephone is used for normal calling receiving purpose.”
Really need help on the connection. I got the circuit ready and a normal telephone set ready. But how do i connect the telephone set line to my circuit (To my KT3170)???
Also for testing purpose, do i need to connect all output pins of IC74154 to some appliances or can i just connect few of the output pins and the rest left it unconnected.
Looking forward for your reply, thanks a million in advance!
September 16th, 2009 at 1:25 pm
i want its circuit diagram
September 25th, 2009 at 10:45 am
i want its circuit diagram
October 3rd, 2009 at 11:48 am
sir can u suggest me a circuit through which i can control a toy car using two cell phone one on the car & other on the my hand
October 3rd, 2009 at 11:50 am
i want its circuit diagram
October 13th, 2009 at 8:21 am
send me all d information abt dis project including circuit digrams, etc..
October 30th, 2009 at 1:20 pm
please send me the synophsis of
” appliance control through mobile phone using DTMF”
November 2nd, 2009 at 10:22 pm
i want dis project urgently. how i can get it? pleas reply me fast as possible.
November 9th, 2009 at 4:04 pm
send that software
November 12th, 2009 at 5:38 pm
I am very much interested in this project, if possible instead of telephone can it used with mobile, if yes what sort of changes are required. Pls send me details including components, circuit diagram , software. Pls reply immediately
November 12th, 2009 at 8:34 pm
plz sens me d ckt. diag. of project
device control using mobile
November 26th, 2009 at 9:22 pm
pls send me the working of this project using microcontroller(device control using telephone)
December 2nd, 2009 at 9:31 am
hi,i am very much interested in the project of controlling switch using telephone.please send me the detail information.Thank you
December 6th, 2009 at 9:37 pm
please provide the circuit diagram
December 9th, 2009 at 1:58 pm
i am very interested in this so may you please provide the circuit diagram please
December 11th, 2009 at 12:29 pm
i am interested in doing this project. may i please have the PCB diagram and the list of components asap. thanks.
December 14th, 2009 at 3:29 pm
hello!
i want the fully detail of this project like circuit diagram, componont,discription,blockdiagram.please send me in soft copy in my mail.as m facing interws nw..i made same projct in my final year, but nw nt able to explain it as took areadymade projct bcoz of time scarcity..
plzzz…
i m very thankful to you…
December 18th, 2009 at 3:08 pm
hi shall i do this project for my BE level pls rply me and also send me the exact details and wat will be the cost required for doing this project
December 24th, 2009 at 7:32 pm
I have no idea about the use of ic7 555. Can anybody help me to get out of the problem. Hoping for a reply…….vinodquilon@gmail.com
December 27th, 2009 at 6:29 pm
Hi
I need the ful detail of project(Home appliance controller using DTMF) like circuit diagram, componont list ,discription,blockdiagram,equilanant ICs list that used in this project.
please…….. send me a soft copy in my mail as i m facing interview
I m very thankful to you…
December 30th, 2009 at 3:40 pm
hi
I like the concept the very well.I want more information about Ckt dig, Components, synopsis of Device control using Telephone project. waiting for your reply. Thnx in adavnce.
January 24th, 2010 at 5:16 pm
Sir, pls send me a circuit diagram with complete labels on my email.
January 28th, 2010 at 3:15 pm
Sir, pls send me a circuit diagram with complete labels on my email.
January 28th, 2010 at 9:03 pm
respected sir,
can i get the complete circuit diagram with neat labels and the pcb layout of this project?? plz send it to me on my email id.
thank you.
February 1st, 2010 at 11:03 pm
Please send me the coding and circuit diagram of this project.
February 2nd, 2010 at 1:45 pm
Hi
I need the ful detail of project(Home appliance controller using DTMF) like circuit diagram, componont list ,discription,blockdiagram,equilanant ICs list that used in this project.
please…….. send me a soft copy in my mail as i m facing interview
I m very thankful to you…
February 6th, 2010 at 6:32 am
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…
February 14th, 2010 at 11:55 am
Great project renjith!!!
February 14th, 2010 at 4:10 pm
pls give circuit diagram device control through telephone. using micro controller IC. IC 89S52
February 20th, 2010 at 7:24 am
pls i would like see the circuit diagram and implementation of the project
March 11th, 2010 at 12:17 pm
it is too good but i want some more inf