hello everyone,

i recently finished my first project (car based on 8052 uC with wired remote).

now i want to make remote wireless and i am thinking about dtmf (not rf). i read about it on net (googled it and read many tuts), but don't get anything !!! i dont know about circuits much !!! so please help me !!!
i also found a good site but not get much !!!
http://www.freewebs.com/maheshwankhede/dtmfdecoder.html

i donot konw how to interface phone with these chips( CM8870 and KT3170) and the circuit diagram is very diffcult to understand !!! i dont know what to do ???

Please tell me what problem you are facing..
the circuit given in that website is fairly simple. i recommend you to read datasheet of CM8870 will make you clear about the working of IC and interface.

DTMF also need a wired interface.. are you going to use telephone line?

i want to use a nokia mobile phone (1100) !!! but dont know how to connect it with the circuit (receiver side) !!!
i hav to put all the resistors, capacitors and transistor or they are in build ???

my plane is to call the other phone on car through my phone !!! and then operate the car with my phone !!

oww.. ok.. thats a good idea..
yes you need all resistor caps and crystals..
also you need to make circuit that detect ring and pick the call.. after that directly couple the speaker with CM8870.

so i ahv to open the mobile phone and do the circuit work ???

no.. make use of headset.. just use the speaker wire.. be smart

I think you are planning to interface your nokia phone with the microcontroller and control it by dtmf. you can use the CM8870 as your dtmf receiver. it is very easy to build.. you can use winbond w91312 as your dtmf tranmitter

there is no need to transmit DTMF as there nothing on the user side which can understand DTMF. and ofcourse CM8870 is the best choice for DTMF conversion/reception.

hi can u tell me what is the relay dpot in that circuit and what is the use of that circuit ,and also how can i connect the whole circuit with the headset of the phone as u have mentioned above
do i have to cut the wire of headset and then join it to circuit

hello !!! any help

sorry rahul.. i missed your thread, its not DPOT relay.. its DPDT (dual pole double throw) Relay. Its a type of relay. yes you need to take speaker off by cutting wire.

thanks for the reply !!!

i dont get the use of this DPDT reply !!!

so what is the need of ring detector, i mean nokia has a option to accept the call automatically !!

also i want to ask that the wires are attached to relay or can i attach them to dtmf decoder ???

as perl the link you posted in your first post, that person uses telephone line not a mobile phone. so you can remove relay and directly connect the mobile to MT8870.

can u tell me the use of this relay ???

relay picks up the phone.. when ring is detected.. microcontroller switch on the relay and hence phone is answered.

so even without relay i hav to use ring detector circuit or not ???

Well usually there is facility in every mobile for auto answer, if you enable it.. then you need to decide how to detect if call is activated or not..

One thing you can do is.. use auto answer and ask user to press * to start with the further work.. you can also couple microphone with controller to feed voice response..

i have done everything !!! but i am facing a problem.
i sent the dtmf tone to other mobile then it is taken by cm8870 and output of cm8870 is obtained. then this output is given to microcontroller, and an other output is obtained at other port of microcontroller.
now my problem is that the port does not refresh after the output is obtained. i get same output untill i press another key !!!
i tried to give setb to std (in cm8870) through microcontroller !!
i also tried to refresh the port but no use !!!

You have to wait the end of the dtmf tone; check the stb pin.
Something like this pseudocode



Regards
Gianni

in telephone line interface

the input lines to DTMF is speaker lines or what?

sorry, but i used a mobile phone due to which the circuit not only becomes very simple but the application of this project is also increased.

the speaker(which is kept near the ear) wire is connected to dtmf decoder.

please go through this link
http://onlinetps.com/raghu/