Info on the MT8870 receiver

Discussion in 'The Projects Forum' started by corner_boy, Nov 18, 2008.

  1. corner_boy

    Thread Starter Active Member

    Jun 24, 2008
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    I'm trying to connect the sample circuit like done in the data sheet

    http://www.electronicsforu.com/EFYLinux/circuit/jun2003/CI-2-DTMF.pdf

    I simply just don't know how to connect to the telephone line. Simply put i don't see how to connect it, any assistance from anyone is greatly appreciated. Thank you



    PS if i used a 5.1 volts zener diode instead of a 5.6V would that be a problem. I also have 6.1V available.
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
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    The connection is pretty clearly shown (notice the two lines identified as "phone line"). Or are you asking about how to physically connect to the phone line? I would build it with an RJ-11 connector and just use a molded telco cable. The red and green wires are usually the ones in use.

    This is probably going to be difficult except on a printed circuit board. That also applies to your digital record/playback IC. If you search the forums, you will find several threads that discuss how to go about making PCB's, including links to freeware CAD programs to do the layout.
     
  3. corner_boy

    Thread Starter Active Member

    Jun 24, 2008
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    ya im asking how to physically do it.

    do you know about the 5.6V zener diode question i asked though?
     
  4. beenthere

    Retired Moderator

    Apr 20, 2004
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    5.1 volts would be better than the 6.1. As lons as you're taking the trouble, why not get the 5.6?

    See my previous post about the connection. To expand a bit, make it so a telephone extension cord plugs into an RJ-11 modular connector. You can obtain them that will mount to a chassis and wire into a PCB, or ones that mount on a PCB.

    This is a big project, but you can learn quite a lot from doing it.
     
  5. corner_boy

    Thread Starter Active Member

    Jun 24, 2008
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    im waiting on the 5.6volts in the mail, i only ask because those are the closest availible now
     
  6. corner_boy

    Thread Starter Active Member

    Jun 24, 2008
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  7. beenthere

    Retired Moderator

    Apr 20, 2004
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    Xtal is shorthand for crystal. Those 3.57 MHz crystals used to be common as dirt because they were used for the color burst oscillator in TV's. They are probably still available.

    Here's a link for some info - http://en.wikipedia.org/wiki/Crystal_oscillator.
     
  8. corner_boy

    Thread Starter Active Member

    Jun 24, 2008
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    oh wow, thanx. any idea on where to purchase that online?
     
  9. beenthere

    Retired Moderator

    Apr 20, 2004
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    Mouser has them. Try part #695-HC49US-357-U @$0.58.
     
  10. corner_boy

    Thread Starter Active Member

    Jun 24, 2008
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    thank u "beenthere"


    ---> I had a question in the wire connection. The phone line to wall has 4 wires and I'm sure which one will go to what side of the diagram in the link i provided earlier.

    anyone have an idea or should i just plug and pray for the best, =)
     
  11. Audioguru

    New Member

    Dec 20, 2007
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    In North America, the green and red wires are used in a 4-wires telephone line. The yellow and black might be used for a second telephone line.
     
  12. corner_boy

    Thread Starter Active Member

    Jun 24, 2008
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    thanx for that.

    I did it at my house and the thing worked perfectly thanx. But i attempted at my skool, and im guessing because its in a network it didnt work with the red and green. But i also connected the black and yellow with it and it only caused silence in the phone.
     
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