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Can MT8870 DTMF decoder module handles none audible signals?

Hi great members,
I've a question that never been answered. I'd like to use DTMF decoder with 8870 chip but before I order it globally, I tested normal calls between cellphones and no DTMF detected and after some research I got that mobile network is transmitting DTMF as digital signals without audible tones.

So that DTMF decoder will never work as same as SIM800L or even any other GSM modules Is that true? If yes, I'd look for any solutions should I connect a sound amplifier or extra pieces of electronics or even dealing with phone settings?

I've read too many about DTMF technology and it's improvements history on another hand I couldn't find in MT8870's datasheet any info to help me get my question answered.

I hope to find clear answer about It's possibility it can or not. Witch DTMF decoder, GSM modiles (e.g. SIM800), USB GSM modem or any GSM phone models can do the task.

Thank you all
 
Thank you so much for your replies @Visitor @KeepItSimpleStupid

I don't believe any cell phone will transmit or recognize DTMF tones. All the switching info is transmitted digitally.
But Why if I make a call from cellphone to landline phone, it recognized DTMF and played it's tone while the call.

I do know that my cell phone carrier had to enable something so FAX and modems would answer. Otherwise, they hang up.
I belive it was CSD or Circuit Switched Data. https://en.wikipedia.org/wiki/Circuit_Switched_Data A Motorola Razer V3 had a built-in FAX modem.

Edit: CSD acronym
That's totally new to me, I will read about CSD and HSCSD.


I also need to know about SIM800/900 or any GSM modules If any has experience with it's DTMF feature.
 

Nigel Goodwin

Super Moderator
Most Helpful Member
Thank you so much for your replies @Visitor @KeepItSimpleStupid


But Why if I make a call from cellphone to landline phone, it recognized DTMF and played it's tone while the call.


That's totally new to me, I will read about CSD and HSCSD.


I also need to know about SIM800/900 or any GSM modules If any has experience with it's DTMF feature.
DTMF is old obsolete analogue technology - why would you even want to use it?. I'll also be very wary about obtaining chips - it's the sort of thing that Chinese criminals will print fake labels on different chips and send them to you, it seems unlikely they are still manufactured?.

Obviously you can talk over a cellphone, so you can send DTMF over a cellphone - but you need to initiate a voice call first.

What are you actually trying to do? - and why aren't you using a much more modern method?.
 
DTMF is old obsolete analogue technology - why would you even want to use it?
Hello, I'm Arduino starter and wanted to implement a remote home automation project and there are too many tutorial about that but no one considered that nowadays dial pad keys tones are sent digitally with no tones. I didn't know what is this way called but after reading too many about DTMF history I got that it still exists till today but with improvements and new methods of signaling.

That's what I hope to do with Arduino just home automation via a normal call, but I got shocked when I tested this DTMF with no luck to get it to work.

I'll also be very wary about obtaining chips - it's the sort of thing that Chinese criminals will print fake labels on different chips and send them to you, it seems unlikely they are still manufactured?.
That's already happened with a friend he got faked ones!


Obviously you can talk over a cellphone, so you can send DTMF over a cellphone - but you need to initiate a voice call first.
Below are some of what I tested with calls:
1. Tried to make call cross net or on net between many phones (smart/old) with no luck to get working.
2. A friend living in another area and for somehow it worked with him, I guess It's related to area network upgrade happened in my area.
3. Tested an international phone call and no audible DTMF tones.
4. The only case worked that when I made call to landline it captured that tones (I couldn't understand why it called fake tones).
5. Tried to disable dial pad tones in android and calling any IVR service and It still work with no Issues.
6. DTMF Problems Troubleshooting
7. Sending DTMF through voice channel by switching to speaker during the call but bad result.
 

Visitor

Well-Known Member
....I'll also be very wary about obtaining chips - it's the sort of thing that Chinese criminals will print fake labels on different chips and send them to you, it seems unlikely they are still manufactured?.
Nigel, a tiny bit of research shows that DTFM decoders and transceivers are in current production by those "Chinese criminals" at Microchip (you know, the company that makes PIC and Atmel microcontrollers). Over 10,000 decoders are in stock at the usual suppliers (e.g., over 7000 at Digikey).


And I must admit, I had forgotten about touch tones used to navigate phone tree systems. So while I don't believe you can initiate a call from a cell phone using touch tones, a cell phone is capable of generating them.


Screenshot_20210411-025914_Edge.jpg
 

rjenkinsgb

Well-Known Member
Most Helpful Member
Interesting!
I'm guessing that the tones are sent, but muted by the receiving phone audio processing system?

I have an alarm system with an interactive voice / keypad menu. That works fine from either a land line or mobile phone

Calling between the land line and mobile, the mobile phone mutes the tones from the land line phone (which is on an analog line) - but the land line phone does not mute the tones from the mobile phone.

I tried blowing on the mic of the land line phone so there is a constant background noise. Pressing a key causes a brief mute in the audio received by the mobile phone...

A bit of research finds this in relation to the SIM800L:
Enable DTMF: AT+DDET=1,1000,0,0 (see AT commands datasheet for parameters)
I don't have one, but the implication is that disables the DTMF audio muting?
 
I'm guessing that the tones are sent, but muted by the receiving phone audio processing system?
Ya! I thought too but I got confused because same mobiles was sending and receiving DTMF signals normally about 2 years ago using same mobile carrier in same area.

I have an alarm system with an interactive voice / keypad menu. That works fine from either a land line or mobile phone
Is that using GSM based modem or via VoIP/SIP PBX?

I hope also If anyone can clarify about DTMF features and advantages with that SIM800L if it really can handles any methods of DTMF or not.

The MT8870D/MT8870D-1 is a complete DTMF receiver integrating both the bandsplit filter and digital decoder functions. The filter section uses switched capacitor techniques for high and low group filters; the decoder uses digital counting techniques to detect and decode all 16 DTMF tone-pairs into a 4-bit code.
MT8870D datasheet | microsemi.com [Oct 2006]
 

rjenkinsgb

Well-Known Member
Most Helpful Member
Apparently the SIM800 does the DTMF detection internally and sends the results over the serial port; if it has the appropriate firmware and you enable that function with the AT command I mentioned earlier.

See more info here:

Also for SIM900
 

KeepItSimpleStupid

Well-Known Member
Most Helpful Member
Way back, ages ago, the 1960's. The Bell System used "in-band" signalling. It's DTMF and a few more tones. 2600 Hz was disconnect billing. So, with a "blue box" you could dial a long distance number (any would do) and dial your neighbpr via a satellite link if you desired. At that point in time, the tones were heard when the system was making the call for you.
If you made a long distance call and sent the pure 2600 Hz tone, then billing stopped

SS7 or Signalling System 7, put the control signals out-of-band.

==

VoIP has been struggling with FAX modems, but I think it's been getting better.

A useless read: https://www.patton.com/solution/fax-modem-over-ip/

Old document, possible useful info. https://www.itu.int/rec/dologin_pub.asp?lang=e&id=T-REC-V.150.1-200301-I!!PDF-E&type=items
 
Apparently the SIM800 does the DTMF detection internally and sends the results over the serial port; if it has the appropriate firmware and you enable that function with the AT command I mentioned earlier.

See more info here:

Also for SIM900
Yes, I posted comment in many issue discussions for some repos but no clear How it handle DTMF "Internally".

Way back, ages ago, the 1960's. The Bell System used "in-band" signalling. It's DTMF and a few more tones. 2600 Hz was disconnect billing. So, with a "blue box" you could dial a long distance number (any would do) and dial your neighbpr via a satellite link if you desired. At that point in time, the tones were heard when the system was making the call for you.
If you made a long distance call and sent the pure 2600 Hz tone, then billing stopped

SS7 or Signalling System 7, put the control signals out-of-band.

==

VoIP has been struggling with FAX modems, but I think it's been getting better.

A useless read: https://www.patton.com/solution/fax-modem-over-ip/

Old document, possible useful info. https://www.itu.int/rec/dologin_pub.asp?lang=e&id=T-REC-V.150.1-200301-I!!PDF-E&type=items
That's a good point to reach, Thank you for your shared info. Is that SS7 is a new signaling method of DTMF or It's totally different and not in DTMF domain?

If that is out of DTMF domain and new generation in telecommunication signaling. So It's so clear to say such GSM modules shouldn't work at all because it's clearly support only DTMF

Can any device handle this SS7? Or it's totally filtered/banned from mobile operator network to be sent to any mobile during the call?
 

atferrari

Well-Known Member
Define what is audible for you:

For your reference an audible tone for my grandson ranges well above 15 KHz, for me my top tone is around 4 KHz.

Have you even read the respective datasheet?
 
I give up.
I'm going to kill my self in my room :(

Define what is audible for you:

For your reference an audible tone for my grandson ranges well above 15 KHz, for me my top tone is around 4 KHz.

Have you even read the respective datasheet?
Hello atferrari, Sure I read about MT8870 many times but with no luck to get any info related to my problem. and about SIM800L doesn't contain any technical details about DTMF feature except some commands.

Ok I'd like to say I'm not telecommunication engineer and what I mean about non-audible, the way we send keypress events during the call witch still used in telephony systems witch called Dual-tone multi-frequency signaling (DTMF).

But for mobile systems it got many changes and improvements, some resources I read that this DTMF still being used and signals sent digitally as events.

So if a caller (A) tried to press any keys the receiver (B) will not hear this key tones during normal call. I don't know why most of Arduino users and youtubers don't know about the problem we face. Are the mobile network operators in my country owned by Elon Mask!

Are there no users around world don't hear key tones during the call [No DTMF]?

I feel that I'm stupid to find the problem to describe it to experts. And sorry my mother tongue is not English but I'm going to forget it soonest.

below troubleshooting may clarify more about the problem

1. Tried to make call cross net or on net between many phones (smart/old) with no luck to get working.
2. A friend living in another area and for somehow it worked with him, I guess It's related to area network upgrade happened in my area.
3. Tested an international phone call and no audible DTMF tones.
4. The only case worked that when I made call to landline it captured that tones (I couldn't understand why it called fake tones).
5. Tried to disable dial pad tones in android and calling any IVR service and It still work with no Issues.
6. DTMF Problems Troubleshooting
7. Sending DTMF through voice channel by switching to speaker during the call but bad result.
 
FYKI. Someone told me that Samsung Galaxy A10 Can detect DTMF digital signals, Although I tested the below devices but I will give it a try.

[Android phones]
Honor 7A
Meizu C9 Pro
Lenovo Tab A3300
Lenovo A1000
Nokia 3.2
Samsung Galaxy S Duos S7562

[Java phones]
Nokia 3110c
Nokia 1200
LG T-375
GTide (Can't remember it's model)



I'm confused if this problem caused by mobiles itself or from operator's network side or both?
 

ChrisP58

Well-Known Member
Most Helpful Member
There is some way of sending key presses from a mobile phone to an end device.

I use my phone to refill prescriptions with my pharmacy. I call their automated number and press keys to navigate their menu system. I hear a beep when I press a number, but it's the same tone for all keys. But the system on the other end knows what number I pressed.

I then called my desk phone. When I press a number on my mobile, I hear a beep in my mobile, but nothing from my desk phone receiver.

So there is a way to do it. But it doesn't appear to be DTMF.

My phone is a Samsung Galaxy 7 Edge.
 

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