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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
      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
        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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