injecting dtmf to the telephone line

[jeanninemtv]

hi guys
i have a little problem

As everyone knows dtmf generation is possible in basic with dtmfout command
i tried it

using portb.0  and a 10k resistor connected to the + terminal of the diode bridge , the - terminal to ground and AC1 and AC2  to tlf line.

tones works not fine as i waited but my only big problem is that line dont recognize the "0" tone from pic.


Could anyone suggest me any good interface and reliable to inject this pwm signal to the lin?


Thanks Again.

[EDSONCT]

"0" must genereted high frequency
You can check filter and pwm frequency.

Edosn

[aslan_korhan]

Better use TP5088 or another DTMF generator IC with the PIC. It's signal is much cleaner.

[Stefkeb]

Hi,

I have no experience using a PIC to generate clean DTMF signals, using a dedicated chip as mentioned above will certainly give a working clean signal.
Please be reminded that for a reliable use of DTMF your signals need be clean !

What kind of transformer are you using to couple the signal to the line ?

Best regards,

Stef.

[titi]

Hello,

In this link they explain how inject BF signal in phone line:

http://www.tkk.fi/Misc/Electronics/circuits/teleinterface.html

Bye.

[Parmin]

This is a link to a PIC controller DTMF dialer alarm

Code:

http://users.tpg.com.au/users/talking/DialAlarm-1-Page1.html

Par

[jeanninemtv]

I am not using transformer.
I am using the following


0----VVVV----o-----vvvvv------0----dtmfout
                    !                        !
                    !                        !
                   ==                     ==
                    !                        !
                    !                        !
0---------------------------------  gnd

R:  1k, C = 100n, using suggestion from crownhill pds
then i connect the

dtmfout  * +        ac1  *------
            *                  *      to line
            *                  *     
gnd       *  -         ac2 *------


testing it works with all numbers but not work with "0" digit.....

help!!!!

i have no transformers available yet...

[dazheng]

Hi jeanninemtv have a peek for this site regarding telephone interface, hope it will helps..
http://www.epanorama.net/circuits/teleinterface.html

dazheng

[Parmin]

Jeanine, the link I gave above does not use transformer.

[hate]

Did you checked the generates frequencies by the compiler when you enter '0' as data? Maybe it generates some other frequency for other dtmf tones like '*','#' or the ABCD tones!

Regards...

[jeanninemtv]

thanks parmin, you are right... your suggestion has no transformer....  i will try it today.

BTW  i didn't analalyse output for proton dtmfout "0".

But i think i can use sound2 command to generate 2 tones to emulate 0 and the rest of digits with dtmfout and 2nd pin of sound2 in state '0'


I'll write back for feedback...

One more questionç

i need to hook off calling with the  board, but i can't.

Any suggestion ?   if i dont attach a phyisical telephone i cant hook off....   any circuit for emulate telephone impedance?

Thanks.

And yes, i will attach photos, dont worry

[jeanninemtv]

Well

important..

i forgot that 0 from telephone keypad ys a 10 in mt8870 outuput   

tone generation solved ... parmin your circuit helps so much to smooth the tone, yet with dtmfout command!

now i have the following problem.

i have no availability of 600 ohms transformers.
Is there any form to build any circuit with the same purpose???

I need a transformer to extract 2 signals separated :   The thinks i speak to the other person and what he speaks to me from the other side of the loop

how to separate both signals?  i am not speaking about connecto to a speaker or amplif.  Just extract the conversation signals and transfer them to another LOOP.  That's why i think i need to avoid the use of trafos because i have no trafos available...

At this moment i use 2 telephones together
one for 2st loop attached to my circuit
and the other connected to the other line
the headset
spk and microphone  from telephone  are connected this way.


spk1 '''''''''''''''''''''''''''''''''''''''''''''''''    mike2


mike2'''''''''''''''''''''''''''''''''''''''''''''''''   spk2

the coupling is via audio transformers
i need to send to hell the 2 telephones and integrate the complete interfaceing into my board....

2 telephones and 2 transformers of audio makes a lot of space....  not an intelligent solution, and a lot off echoe is added....

[localcrack]

you may use UM91214 and uPD22100 Ic to generate DTMF with microcontroller

[Parmin]

I need a transformer to extract 2 signals separated :   The thinks i speak to the other person and what he speaks to me from the other side of the loop

I never did this before, but I think it is interesting..

My theory is to somehow encode and compress the audio signal into a timesharing system.

So, you capture some say 10ms of audio from the Unit1, encode and compress, then capture the next 10ms of the unit 2, and while you encode and compress unit 2, you uncompress and decode signal from unit 1 and vice versa.  Timing is the critical factor in this. The transmission system is in digital state so the coherence of signal is much better over longer distances with lower transmit power.  I say to use 10ms , but you could use any time period as long as the resultant signal is still coherent and resemble natural speech.

Ahh.. ummm  I confuse myself.. I need more beer...

Par.

[EDSONCT]

HT-9200 is very simple and cheap.
Edson

[jeanninemtv]

Answer for parmin:

Hi Par,

YEs i need to solve the problem ,

1:  the circuit can hook on-off the calling.  (it works but i need to plug a telephone too, i need to kick off this telephone. how to replace to emulate the impedance correctly?)
2:  dtmf input and reading of numbers ok...
3:  dtmf out for calling ... in process...
4:  MAIN PROBLEM:   EXTRACT THE CONVERSATION IN AND OUT CHANNELS AND SENT THEM TO ANOTHER LINE.... WHY?  LET ME SEARH IN A DICTIONARY TO ANSWER LATER.... 
5:  THE CIRCUIT FROM (4) WILL BE USED WITH ANOTHER LINE AND THEN CREATING A KIND OF LINKING BETWWEN 2 LINES.... 

[Parmin]

Jeanine,
are you trying to make a sort of conference call?
or would it be like an old relay station where the operator is relaying calls from one phone to the other?

As to extract the conversation, what is the limitation beside the 600ohm transformer? Why dont you go buy a cheap chinese phone and extract the inside? the phone would have the isolating circuit for the input and output speeches.  Here in Aussie, they are quite cheap and you could get a transformerless model for less than $10 AUD.  It should solve the problem cheaply.

Otherwise, I will need to know exactly what you are trying to achieve before I could comment on them.

Par.

[ipek]

easy optical isalation barrier for phone line and ide.....
http://rapidshare.com/files/71359019/Phone_Link.rar.html

[notme]

Hello jeanninemtv,

It sounds like you have two problems:
1. You need to separate the transmit and receive signals from the phone line
2. You need to generate an off-hook condition by drawing sufficient dc current

Suggested solutions:
1.  An analogue phone line is balanced so that it can carry conversation in both directions simultaneously.  To separate the two signals (channels) you need a 2-wire to 4-wire converter or a hybrid.  Have a look on the Microchip site and search for App Note AN854.  There you will find a good example of a hybrid using op amps.  You can connect your DTMF generator or microphone to the TX line.  The RX line will have the incoming signal.  Don't worry about the transformer.  You can replace it with two 470nF capacitors.  They will block the dc from the phone line and provide about 600 ohms impedance at 1kHz.  You should also consider using a varistor or clamping diodes to protect the circuit against high voltage when the line is ringing - 90V rms! 

2.  To put the line in an off-hook conditon you need to draw around 20 - 60 mA dc.  You must be careful not to short out the ac signal.  For this you need a circuit that has low impedance at dc, but high impedance at higher frequencies 300Hz - 3.4kHz.  Have a look at Tech Note TN11 on the Midcom site: http://www.midcom-inc.com/Tech/TechNotes.asp.  There are a few dc holding circuit suitable for use on phone lines.

Hope this helps.         

[amatuere]

hello!
hope it can help!
-Application note by microchip AN854

[amatuere]

hello!
 I also have a problem regarding injecting DTMF tones to a landline using cellphone touch tone.
i try to make a cellphone to landline interface, the principle is that when you call the slave phone
it will automatically answered by giving you a side tone from landline, there you can dial thru your cellphone's touch tone the number you like to call. still on the process.  cellphone to cellphone call with the same network is very cheap unlike when you call from cellphone directed to landline was double the cost in my country.  any suggestion?

kobi

[jeanninemtv]

Time to read out an854...

[amatuere]

greetings!

still trying to send dtmf to to dial at the other end, no luck at all.  :(i am using the midcom's low cost DAA/FXO circuit. the tx audio is connected to speaker pin  of nokia 3310, likewise the rx to microphone. do i something missing?

73!
kobi

[jorge7458]

Hello: 
I have generated with picbasic tones dtmf without inconveniences. The used hardware was that of the manual but I included in parallel with it lines her phone a resistance of 680 ohms. 
Jorge

[amatuere]

hello!
  i already tried, no luck! mine dtmf tone was generated by the cellphone not by pic. hmmm well
need more test!

73 to all!

kobi