+ Post New Thread
Results 1 to 8 of 8
  1. #1
    Advanced Member level 5
    Points: 16,720, Level: 31
    Achievements:
    7 years registered
    neazoi's Avatar
    Join Date
    Jan 2008
    Location
    Greece
    Posts
    3,377
    Helped
    13 / 13
    Points
    16,720
    Level
    31

    1200 baud data transfer over audio passband of cellphone. Is that possible?

    1200 baud data transfer over audio passband of cellphone. Is that possible through the use of their codecs? Has anyone actually tried it? There are videos about comms on 300 baud but how about 1200 baud, has anyone ever tried it?
    Professional engineering is the top, but amateur engineering is more fun.
    It is when you cross the barrier between these two, that things become really fascinating!

    •   AltAdvertisement

        
       

  2. #2
    Super Moderator
    Points: 81,741, Level: 69
    Achievements:
    7 years registered
    Awards:
    2nd Helpful Member
    betwixt's Avatar
    Join Date
    Jul 2009
    Location
    Aberdyfi, West Wales, UK
    Posts
    13,409
    Helped
    4471 / 4471
    Points
    81,741
    Level
    69

    Re: 1200 baud data transfer over audio passband of cellphone. Is that possible?

    Audio bandwidth goes to about 3KHz so it should be possible but almost all cell phones have serial interfaces already if you know how to access them. Why not just use the built in UART directly and get the benefits of error correction and speeds of 9600 Bauds or better?

    Brian.
    PLEASE - no friends requests or private emails, I simply don't have time to reply to them all.
    It's better to share your questions and answers on Edaboard so we can all benefit from each others experiences.



    •   AltAdvertisement

        
       

  3. #3
    Advanced Member level 5
    Points: 16,720, Level: 31
    Achievements:
    7 years registered
    neazoi's Avatar
    Join Date
    Jan 2008
    Location
    Greece
    Posts
    3,377
    Helped
    13 / 13
    Points
    16,720
    Level
    31

    Re: 1200 baud data transfer over audio passband of cellphone. Is that possible?

    Quote Originally Posted by betwixt View Post
    Audio bandwidth goes to about 3KHz so it should be possible but almost all cell phones have serial interfaces already if you know how to access them. Why not just use the built in UART directly and get the benefits of error correction and speeds of 9600 Bauds or better?

    Brian.
    I could possibly, but "regular" users couldn't.
    Anyway I have just tested it. I connected a smart phone from it's hands free port to the PC mic and phones. then I called the smart phone from a land line at home.

    It could not even send 110 baud. It started sending them ok but after 1-3 seconds they were suppressed. Continuously changing the AF volume to 0% and then back to a percentage tricked the codec somehow.

    Sending pulses of a single tone passed ok.
    Also, sending a dual tone passed ok.

    But not FSK at 110, 300 or 1200baud, they all seemed to have this problem I mentioned.

    Now, I do not know if this is due to the mobile phone codecs or the landline phone codecs, as I have not tried it with two mobile phones yet.
    Professional engineering is the top, but amateur engineering is more fun.
    It is when you cross the barrier between these two, that things become really fascinating!



    •   AltAdvertisement

        
       

  4. #4
    Advanced Member level 5
    Points: 17,503, Level: 32
    Achievements:
    7 years registered

    Join Date
    Nov 2012
    Posts
    3,199
    Helped
    790 / 790
    Points
    17,503
    Level
    32

    Re: 1200 baud data transfer over audio passband of cellphone. Is that possible?

    But not FSK at 110, 300 or 1200baud, they all seemed to have this problem I mentioned.
    There are several types of FSK (IIRC)- can you be somewhat more specific?

    Also, try to insulate from external noises. I remember using phones fixed in rubber cups of a modem. If the fit was not tight, the connection went dead (disconnected).

    My memory is rusty, but there are several dual tones that act as control signal for the modem (out of the 16 possible dual tones, only 12 are present on the keyboard).- perhaps google can help!!

    What is the exact setup (some more details please!!)?



  5. #5
    Advanced Member level 5
    Points: 16,720, Level: 31
    Achievements:
    7 years registered
    neazoi's Avatar
    Join Date
    Jan 2008
    Location
    Greece
    Posts
    3,377
    Helped
    13 / 13
    Points
    16,720
    Level
    31

    Re: 1200 baud data transfer over audio passband of cellphone. Is that possible?

    Quote Originally Posted by c_mitra View Post
    There are several types of FSK (IIRC)- can you be somewhat more specific?

    Also, try to insulate from external noises. I remember using phones fixed in rubber cups of a modem. If the fit was not tight, the connection went dead (disconnected).

    My memory is rusty, but there are several dual tones that act as control signal for the modem (out of the 16 possible dual tones, only 12 are present on the keyboard).- perhaps google can help!!

    What is the exact setup (some more details please!!)?
    Just a simple audio cable connected to the hands free socket of the mobile phone and on the other side to the microphone and headphones jacks of the PC. There is no acoustic coupling. Bell 202 is the scheme interested the most, but I have tried other standards at lower bit rates.
    Professional engineering is the top, but amateur engineering is more fun.
    It is when you cross the barrier between these two, that things become really fascinating!



  6. #6
    Advanced Member level 5
    Points: 17,503, Level: 32
    Achievements:
    7 years registered

    Join Date
    Nov 2012
    Posts
    3,199
    Helped
    790 / 790
    Points
    17,503
    Level
    32

    Re: 1200 baud data transfer over audio passband of cellphone. Is that possible?

    I am puzzled: it should work without fuss.

    Just for debugging: record a 1min fax transmission signal and play it on the smartphone. Does it still drop the connection?



  7. #7
    Advanced Member level 4
    Points: 7,568, Level: 20
    Achievements:
    7 years registered

    Join Date
    Jul 2010
    Location
    Sweden
    Posts
    1,013
    Helped
    387 / 387
    Points
    7,568
    Level
    20

    Re: 1200 baud data transfer over audio passband of cellphone. Is that possible?

    Landline phone stations transferred the actual audio samples with 8 bits non-linear sampling at 8 kHz = 64 kbits/s.
    Cell phones tries to get similar audio quality with a much lower bit rate. To achieve that they use a model of the human voice generation,
    so it isn't audio samples that are transferred.
    It is not surprising that it is difficult or impossible to use normal "analog" modems.



    •   AltAdvertisement

        
       

  8. #8
    Advanced Member level 5
    Points: 17,503, Level: 32
    Achievements:
    7 years registered

    Join Date
    Nov 2012
    Posts
    3,199
    Helped
    790 / 790
    Points
    17,503
    Level
    32

    Re: 1200 baud data transfer over audio passband of cellphone. Is that possible?

    Cell phones tries to get similar audio quality with a much lower bit rate. To achieve that they use a model of the human voice generation,
    That is very interesting information: I was not aware (obviously). But how the landline to cellphone (and vice versa) calls work? And many love to listen to music on their cell phones (nothing great, but good for morning jogging or at the gym).

    It will be nice to see whether it blocks DTMF frequencies used in the landline keypads.



--[[ ]]--