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Digital potentiometer

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  • scott@opentrac.org
    As an experiment, I replaced the TX pot in one unit with a DS2890 1-wire digital potentiometer and added a TXLEVEL command to control it. It works - and only
    Message 1 of 3 , May 7, 2006
      As an experiment, I replaced the TX pot in one unit with a DS2890 1-wire
      digital potentiometer and added a TXLEVEL command to control it. It works -
      and only requires minimal board modifications - but the part doesn't seem to
      be readily available anywhere. I'm going to keep it in mind for future
      revisions.

      If anyone has a DS2890 (TO92) and wants to try it out, let me know and I'll
      give detailed instructions. You need to cut one trace, bridge two pads, and
      run a jumper.

      Scott
    • Ian ZL1VFO
      Message 2 of 3 , May 9, 2006
        > Message 4
        > From: "scott@..." scott@...
        > Date: Sun May 7, 2006 6:45pm(PDT)
        > Subject: Digital potentiometer

        > As an experiment, I replaced the TX pot in one unit with a DS2890 1-wire
        > digital potentiometer and added a TXLEVEL command to control it. It works -
        > and only requires minimal board modifications - but the part doesn't seem to
        > be readily available anywhere. I'm going to keep it in mind for future
        > revisions.

        > If anyone has a DS2890 (TO92) and wants to try it out, let me know and I'll
        > give detailed instructions. You need to cut one trace, bridge two pads, and
        > run a jumper.

        > Scott

        Just out of curiosity, how are the existing tones generated? It's PWM
        from PTB6, right? Couldn't you just vary the min and max values up &
        down to control the volume, sort of a scaling concept...? Would that
        work? Should save adding hardware if it does...

        -Ian ZL1VFO



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      • scott@opentrac.org
        ... They re PWM, trouble is it s only 16 levels. Adding level control there means either reducing the resolution further, or stretching the PWM cycle period
        Message 3 of 3 , May 9, 2006
          > Just out of curiosity, how are the existing tones generated? It's PWM
          > from PTB6, right? Couldn't you just vary the min and max values up &
          > down to control the volume, sort of a scaling concept...? Would that
          > work? Should save adding hardware if it does...

          They're PWM, trouble is it's only 16 levels. Adding level control there
          means either reducing the resolution further, or stretching the PWM cycle
          period and lowering the carrier frequency. Plus, all of the timing is tied
          to the cycle time.

          The BPSK modulator does manage to get by with a longer PWM period and 256
          levels, and it's got a scaling system built in because of the need to do
          envelope shaping. It's only doing 31.25 bps, though - I'm really not sure
          the same thing will work at 1200 bps. I do intend to have another look at
          it when I get a chance, though.

          Scott
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