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  • dario_alvarez_abal
    Is it possible to receive (and decode) a coded signal from a phone line connecting a receiver device (with a microphone) to the speaker of that phone?? (i
    Message 1 of 64 , Jan 27, 2005
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      Is it possible to receive (and decode) a coded signal from a phone
      line connecting a receiver device (with a microphone) to the speaker
      of that phone?? (i mean, no direct cable connection - instead using a
      speaker and a microphone connection to receive the coded signal that
      could be video+audio)
      Hope i made myself understandable, since i see this very difficult to
      do because there could be lost signal and amplification.
      Regards
    • Rick Sparber
      Kerim, It is funny what consumers latch onto for importance. You work hard to get the circuit board down by 0.1 and then have to bolt it to a block of steel
      Message 64 of 64 , Jul 8, 2012
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        Kerim,

        It is funny what consumers latch onto for importance. You work hard to get
        the circuit board down by 0.1" and then have to bolt it to a block of steel
        to get any credibility. Going with a simple resistive load current should
        work fine since delta Vbattery is small.

        I look forward to hearing more.

        Rick

        -----Original Message-----
        From: Electronics_101@yahoogroups.com
        [mailto:Electronics_101@yahoogroups.com] On Behalf Of Kerim F
        Sent: Thursday, July 05, 2012 7:10 PM
        To: Electronics_101@yahoogroups.com
        Subject: [Electronics_101] Re: question

        Rick,

        In my free time (since I work on other projects), I started designing its
        analogue part on LTspice. I will include the digital part using voltage
        sources having each a proper timing list. Since AT89C2051 is an old and
        simple MCU (20-pin), it doesn't have an ADC feature. Instead, it has an
        internal comparator and its two inputs are P1.0 and P1.1 (its output is
        P3.6, an internal flag). So when I need measuring a voltage, I measure for
        example the charging time of a capacitor till its voltage reaches the
        measured voltage. Obviously an external opamp or comparator can also be
        used.

        You are right about the display; a number looks more professional. After
        all, implementing either one is done mainly by software. The irony is that I
        noticed most consumers are impressed more by the size (if not the weight
        too) if it is larger ;)

        To reduce the circuit, I removed the load current regulation. So the current
        will be I_load = V_batt / R_load when R_load is on.

        Measuring V_open (I_load=0) will give
        R_batt = (V_open - V_batt) / I_load
        R_batt = R_load (V_open - V_batt) / V_batt

        The circuit on LTspice is almost finished. When it will be ready, I will
        upload all its necessary files in case some members have LTspice and like to
        play with it :) The software will be next. For instance, since I cannot get
        windows C51 compiler, assembler, debugger and/or emulator, I used (for 30
        years) writing my MCU (or CPU in the past) programs using a text editor and
        DOS assembler (via command line) ;)

        Kerim
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