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RE: [Electronics_101] Re: question

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  • Rick Sparber
    Kerim, I think the circuit could be modified to do what you want. Rather than use comparator C , you would need an amplifier with sample and hold
    Message 1 of 64 , Jul 1, 2012
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      Kerim,

      I think the circuit could be modified to do what you want. Rather than use
      comparator "C", you would need an amplifier with sample and hold
      capabilities. The monitor should work with any reasonable load on the
      battery so could run continuously. I played with this idea back in 1973 when
      I developed an in-circuit ohm meter.

      Rick

      -----Original Message-----
      From: Electronics_101@yahoogroups.com
      [mailto:Electronics_101@yahoogroups.com] On Behalf Of Kerim F
      Sent: Saturday, June 30, 2012 1:31 AM
      To: Electronics_101@yahoogroups.com
      Subject: [Electronics_101] Re: question

      --- In Electronics_101@yahoogroups.com, "Rick Sparber" <rgsparber@...>
      wrote:
      >
      > I have posted two articles in the last few weeks that deal with analog
      > circuits. The response has been underwhelming. Not a single comment.
      > Are there any analog circuit designers left on this BBS?
      >
      >
      >
      > Rick
      >
      > rgsparber@...
      >
      > rick.sparber.org
      >

      Your work reminds me an old small project I was working on but I didn't
      finish it. I liked to measure approximately the DC internal resistance of a
      car acid battery by measuring the small voltage drop on its terminals for a
      known load (DC current).
      Let us assume the battery voltage is 12V and its internal DC resistance is
      about 5mR. If the load current (actually a current pulse with a proper short
      period) is 10A (via MOSFET and current regulator) the voltage drop would be
      50mV. In this case, the ratio of the high side voltage is 11.95/12=0.996.
      This ratio depends on the battery size and its age, for a few.
      I didn't have time yet analyzing attentively your interesting circuit so I
      am not sure how much it may be related to the high side voltage measurement
      that has a very small difference to be measured even approximately. After
      all, the project is just to build a tool for comparing the strength of some
      big batteries under test. I am afraid it will need a few LEDs (instead of a
      display for simplicity).

      Kerim
    • 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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