I want to build a telephone dialer with only mcu

[xxtigerxx]

phone dialer schematic

I want to build a telephone dialer with only mcu.

without a dtmf decoder or encoder.

do you have a any schematic?

THX

 

[xxargs]

telephone dialer schematic

I want to build a telephone dialer with only mcu.

without a dtmf decoder or encoder.

do you have a any schematic?

THX

Detect DTMF without DTMF-circurit with same tolerance for noise etc. is not easy task and need number crunching mcu running whole time if you not want 'non listen ' timeslot. This 'listening' cannot interference with long time interrupts for other job, so programming can be quite complicated and you can forget all powersave or sleep-mode...

In historic is not sucess replace cheap few dollar MT8870 with big huge DSP-card for doing same job...

If you have modem-circurits (pre programmed on-chip DSP) in your design, can in moste case working as DTMF-decoder and coder without problem.

 

[xxtigerxx]

mcu telephone bank

thx xxargs for your advice.

i do not want to detect dtmf now.

i want olny to make a dialer with mcu and detect the state of the line.


THX

 

[hassan1980]

tel dialer schematic

thx xxargs for your advice.

i do not want to detect dtmf now.

i want olny to make a dialer with mcu and detect the state of the line.


THX

DearFriend,

did you build this project, or you are designing it?

because I am looking for this project.

I made searching on the net for the dailer IC then I get PCD3311 and I saw LR4089.

Dear, would you please give me your news for this project?

 

[AndaMan]

project pcd3311

this application note may give you some ideas.

http://www.sxlist.com/images/sxlist/AN6_DTMF_gen.PDF

 

[xxtigerxx]

telephone dialer project

Thx AndaMan
but this is only to produce dtmf.

but how i will transfer to the line and how i will know the line state.

THX


Added after 2 minutes:

Dear hassan1980,

i am at the middle of the project.

i will use a PSOC mcu to produce the dtmf signal.

i will like a schematic how i will speak to the telephone line and how i will read the telephone line state.

 

[John Dekker]

hybrid telephone dtmf signals interface

I have just done a DTMF encoder and decoder with a 18F2520 and it works very well indeed. The encoder works from the mainloop and cycles through a sine table taking pretty much the whole cpu time. The decoder runs from the timer2 interrrupt and uses about 70% of the cpu time. Instead of just checking the 8 dtmf frequencies I check 18 for the dtmf and another 6 for other things. The best application note I found was from Microchip, AN257, and I followed their approach witch gives very good results. I added some extra qualifiers.
It can be done and it is not that hard to implement, you just need to get your head around the algorithm.
I found it easier to make up the sine tables in excel and also to code from scratch rather than following someone elses reasoning.
Have a go, it is immensly satisfying to see it work.
For the zero crossing detecter I used a comparitor inside 18F2520.
I fed a TV chanels audio into the detecter for a day and got no false decodes and also fed the noise from a non TV channel and also had not tones detected to that is pretty robust. It detects a tone from within noise or speech music etc. You can toughen the rules so that it wont but it depends on you application.
I did it with a micro because I had trouble getting a dedicated chip, they seem to be getting scrarce now that most people do it in a micro or dsp.
Regards,
John. ZL2TTM

 

[PaulHolland]

sample schematic mt8870

Look at this: http://www.elan-europe.com/products/com/device/stic.asp microcontrollers with buildin DTMF etc... low cost and designed for your needs.

Paul.

 

[polymath]

dtmf encode build

Hi xxtigerxx

links for MChip AN257 and DTMF

**broken link removed**

**broken link removed**

hope it helps ... Polymath

 

[xxargs]

ic pcd3311

I have just done a DTMF encoder and decoder with a 18F2520 and it works very well indeed. The encoder works from the mainloop and cycles through a sine table taking pretty much the whole cpu time. The decoder runs from the timer2 interrrupt and uses about 70% of the cpu time. Instead of just checking the 8 dtmf frequencies I check 18 for the dtmf and another 6 for other things. The best application note I found was from Microchip, AN257, and I followed their approach witch gives very good results. I added some extra qualifiers.
It can be done and it is not that hard to implement, you just need to get your head around the algorithm.
I found it easier to make up the sine tables in excel and also to code from scratch rather than following someone elses reasoning.
Have a go, it is immensly satisfying to see it work.
For the zero crossing detecter I used a comparitor inside 18F2520.
I fed a TV chanels audio into the detecter for a day and got no false decodes and also fed the noise from a non TV channel and also had not tones detected to that is pretty robust. It detects a tone from within noise or speech music etc. You can toughen the rules so that it wont but it depends on you application.
I did it with a micro because I had trouble getting a dedicated chip, they seem to be getting scrarce now that most people do it in a micro or dsp.
Regards,
John. ZL2TTM

---

Zero cross detect needs big difference betwen wanted signal and unwanted signal (high Signal to Noise ratio) so every zero cross detect dominating by DTMF-signal.

circurits as MT8870 and simular have filter bank and correlators only listing intresting frequensys and not seeing noise outside and this way make higher immunity from interference noise, human vocie and music etc.

Try detect files down here, I don't know if MT8870 detector can recive this (I thinking this working without problem, but have not exemplar to test) , but seems zero-cross detection-methode have little bit truble to handle this file.

I very intrested if you can detect this file


Files is 2 sec to make small size and have 17 numbers in 100 ms tone and 40 ms gap between tones

White noise in files have 'phone' band width, ie. 300-3400 Hz and shall be played in 8 ksampel/sec

---

Good tone detector as CCIR-detector CML FX003 can detect true CCIR-signal so low as -1 dB over noisefloor (ie signal is lower than noiseflor) and use correlator to make sure incoming signal is a sinus tone over time and not part of noise.

simular methode using inside MT8870 for DTMF and describe why need big DSP-card to make same sensitivity and performents as cheap circurits.

 

[xxtigerxx]

how to make a phone dialer

THX you all for the usefull information.

The only think thats missing is a schematic

Does anyone has a schematic how can i speak to the telephone line and be under TVR21.

THX

 

[Ivoi]

mt8870 noise

Texas Instruments have a application note for Generation and Recognition of DTMF Signals With the Microcontroller MSP430

see at **broken link removed**

 

[xxtigerxx]

microchip phone dialer

Ivoi this application have the same with others
but i will like the hardware bitweeen mcu and telephone line

THX

 

[John Dekker]

application pcd3311

I can decode the 19db s/n OK.
I need about 100mV peak to peak into the 18F comparator for good opperation. Doing this with a micro gives great flexibility in what you pass and dont pass. I perform a number of comparisons with both adjacent sidebands and energy distributions among the 24 samples I take. Regards John.

Added after 3 minutes:

Further to my previous reply I think the reason I could not get the 13db file to work was because I have made the inters tone delay about 50mS even though the spec is 40. I did this for my own reasons.
Regards, John.

 

[deepu_ttc]

building a dialer

hello friend its a very good project i thinking of same if you get any info plz share with me

 

[xxargs]

mcu phone project

I can decode the 19db s/n OK.
I need about 100mV peak to peak into the 18F comparator for good opperation. Doing this with a micro gives great flexibility in what you pass and dont pass. I perform a number of comparisons with both adjacent sidebands and energy distributions among the 24 samples I take. Regards John.

Added after 3 minutes:

Further to my previous reply I think the reason I could not get the 13db file to work was because I have made the inters tone delay about 50mS even though the spec is 40. I did this for my own reasons.
Regards, John.

hmm - I impressive you can detect 19 S/N and I thinking your soloution working for > 99% of all practical case - good work

(and is typical for detectors near limits is need more time to make decise if tone exist or not.)

look 19 S/N-file file in sound editor program and you see capture DTMF with only zero cross over-detector is a not longer easy task)

you can possible improve sensitivity if you using band-pass filter so close to used DTMF-tones as possible as front end before your zero-cross detector to shave of all noise outside DTMF-frequency range.

rules for all recivers is not listen wider frequency range as needed for recive information - all noise outside information bandwith only disturb reciver process and consume useful dynamic.


ie if i used 20 KHz BW white noise is possible needs using 28 dB S/N on DTMF for same 'recive' quality as tested 19 S/N-file on your detector if you not have filtred front end.

Added after 4 hours 42 minutes:

This is a generic interface mcu with a telephone line from microchip

Is a good starting schematic to make line interface, Zt and Zl is importent componet to match phone line character for your contry phone line to make best possible supress of outgong signal to reciver side - is also called fork or hybrid. Value of Zt and Zl is differ between contrys depend of used phone line geometry and materials (insulation, distance between conduct etc.) and mostly complex value, ie Zl and Zt can be complex RC(L)-network each.

If you not want cancel/attenuate of outgoing singal in reciver side, you can take away Zl and Zt and make building line interface lot more simple...

trafo is a importent component and influe more or less on hybrid design, for example of 'easy' ferrite pot core line trafo (ETAL1200) have quite complex spice-definition, see fig1, and cannot used directly as AN854 depend of cannot handle phone-line current (magnetic core saturate with small DC-current as 1-2 mA)

Most of small modem-trafo cannot handle DC-current (phoneline can give so much as 100 mA) and needs handle other way (see later in text)

Trafo itself not good to used as 'plugin' directly simular AN854 also after DC-blocking and give not so good match and frequency character (fig2) - trafo needs in most case matched in both end to make more 'invisible' in later fork/hybrid-circurits (fig3) and most telephone companys or goverment want better return loss as 12 dB on lineinterface in 600 Ohm network.


make good cancel of outgoing signal in reciver side in fork/hybride can be very tricky to make. phone station interface and your line interface have (after matching) near 600 Ohm impedance , but phone line itself is not 600 Ohm... and differ depend of length...

if you have situation as high attenuate on phone line with weak recived signal (and needs gain for readable signal) and needs sending strong signal same time - you must building very good line eqvivalent (Zt and Zl) in hybrid to supress 20 - 30 dB
and this Zl and Zt-value can take much time to find out.

---

Example of more complete line interface with DC-loop ballast shows in fig 4, but still need add relay for On/Off hook, ring-detector via opto coupler (make with 10 kOhm impedance for 25 and 50 Hz and working from 25 Volt AC to 110 Volt AC), more high voltage protection etc.

---

 

[saas123qa]

mt8870 dialer

in basic language there is a DTMFOUT, it can helps u in your project

 

[engaydi]

how to build phone dialers

this is pulse dialer only with pic mcu