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Re: [softrock40] 12F683 Question

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  • Mike Young
    Why the diode? ... From: Pete Smith To: Sent: Tuesday, July 01, 2008 6:05 AM Subject: [softrock40] 12F683
    Message 1 of 13 , Jul 1, 2008
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      Why the diode?

      ----- Original Message -----
      From: "Pete Smith" <n4zr@...>
      To: <softrock40@yahoogroups.com>
      Sent: Tuesday, July 01, 2008 6:05 AM
      Subject: [softrock40] 12F683 Question


      > Does anyone know if a 12F683 running on 3.3 volts in the SoftRock 8.3
      > circuit will operate reliably if, instead of using a DIP switch to ground
      > pins on the chip, a rotary switch through a single silicon diode is
      > used. I think that means that the pin will not be at 0, but rather at .7
      > volts above ground, and I can't find any indication in the data sheet of
      > what the chip considers to be the maximum logic low voltage.
    • Pete Smith
      Good question - I am rethinking that, given that I have a separate switch wafer dedicated to frequency control, and another for switching the BPFs. Maybe I
      Message 2 of 13 , Jul 2, 2008
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        Good question - I am rethinking that, given that I have a separate switch
        wafer dedicated to frequency control, and another for switching the
        BPFs. Maybe I can dispense with the diodes on both of those functions. I
        was thinking by analogy to a band decoder, where the same outputs must be
        shared between different sets of choices (like 4 antennas and 6 BPFs).

        73, Pete

        At 12:15 AM 7/2/2008, you wrote:
        >Why the diode?
        >
        >----- Original Message -----
        >From: "Pete Smith" <n4zr@...>
        >To: <softrock40@yahoogroups.com>
        >Sent: Tuesday, July 01, 2008 6:05 AM
        >Subject: [softrock40] 12F683 Question
        >
        >
        > > Does anyone know if a 12F683 running on 3.3 volts in the SoftRock 8.3
        > > circuit will operate reliably if, instead of using a DIP switch to ground
        > > pins on the chip, a rotary switch through a single silicon diode is
        > > used. I think that means that the pin will not be at 0, but rather at .7
        > > volts above ground, and I can't find any indication in the data sheet of
        > > what the chip considers to be the maximum logic low voltage.
        >
        >
        >------------------------------------
        >
        >Yahoo! Groups Links
        >
        >
        >
      • Pete Smith
        Unfortunately, I need 4 outputs, because the codes for several bands use the 4th digit. Actually, I think I have a super-simple solution - I ll test it and
        Message 3 of 13 , Jul 2, 2008
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          Unfortunately, I need 4 outputs, because the codes for several bands use
          the 4th digit. Actually, I think I have a super-simple solution - I'll
          test it and post description later.

          73, Pete

          At 06:13 PM 7/1/2008, jeffthom99 wrote:
          >--- In softrock40@yahoogroups.com, Pete Smith <n4zr@...> wrote:
          > >
          > > Does anyone know if a 12F683 running on 3.3 volts in the SoftRock 8.3
          > > circuit will operate reliably if, instead of using a DIP switch to
          >ground
          > > pins on the chip, a rotary switch through a single silicon diode is
          > > used. I think that means that the pin will not be at 0, but rather
          >at .7
          > > volts above ground, and I can't find any indication in the data
          >sheet of
          > > what the chip considers to be the maximum logic low voltage.
          > >
          > > 73, Pete N4ZR
          > >
          >Hi Pete,
          >
          >To use a single pole rotary switch, add a TTL 8-to-3 encoder (74xx148)
          >and pull any one input to ground at a time. The output will be the 3
          >digit binary number reflecting the highest input that is Low when all
          >below it are high. Inputs will tend to float high in the absence of
          >large signals, so the encoding will reflect the position of the
          >grounded pin. I used this a lot 'back in the day' with the LS family
          >without pull-up resistors (YMMV with other families). Wire the chip
          >in 'dead bug' style and bridge a 0.1 uf chip between Vcc and Gnd. and
          > let us know how this works for you.
          >
          >73 de Jeff, KB3NAX
          >
          >
          >------------------------------------
          >
          >Yahoo! Groups Links
          >
          >
          >
        • brainerd@wildblue.net
          ... I don t know if the 12F683 has internal pull-ups. If so, then a single wafer switching between ground and open will suffice. Generally with CMOS, an open
          Message 4 of 13 , Jul 2, 2008
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            On 2 Jul 2008 at 7:20, Pete Smith wrote:

            > Good question - I am rethinking that, given that I have a separate switch
            > wafer dedicated to frequency control, and another for switching the
            > BPFs. Maybe I can dispense with the diodes on both of those functions. I
            > was thinking by analogy to a band decoder, where the same outputs must be
            > shared between different sets of choices (like 4 antennas and 6 BPFs).
            >
            > 73, Pete
            >
            I don't know if the 12F683 has internal pull-ups. If so, then a single wafer switching between
            ground and open will suffice. Generally with CMOS, an open input is undefined, so it must
            either be pulled up to Vcc or down to ground at all times. The only issue in connecting to
            ground is making sure the pin cannot be an output when it is connected to ground.

            Dave - WB6DHW
            <http://wb6dhw.com>
          • Pete Smith
            Well, connecting to ground is exactly what the DIP switch on the 8.3 Xtall board does. It has pull-ups and also series protective resistors against the kind
            Message 5 of 13 , Jul 3, 2008
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              Well, connecting to ground is exactly what the DIP switch on the 8.3 Xtall
              board does. It has pull-ups and also series protective resistors against
              the kind of unintentional output scenario you describe. Seems like a good
              design.

              On another subject, after thinking a bit more, I will still need the
              steering diodes to keep from unintentionally tying input lines together,
              because of the different combinations needed for the 6 center frequencies
              of interest.

              73, Pete N4ZR

              At 11:21 AM 7/2/2008, brainerd@... wrote:
              >On 2 Jul 2008 at 7:20, Pete Smith wrote:
              >
              > > Good question - I am rethinking that, given that I have a separate switch
              > > wafer dedicated to frequency control, and another for switching the
              > > BPFs. Maybe I can dispense with the diodes on both of those functions. I
              > > was thinking by analogy to a band decoder, where the same outputs must be
              > > shared between different sets of choices (like 4 antennas and 6 BPFs).
              > >
              > > 73, Pete
              > >
              > I don't know if the 12F683 has internal pull-ups. If so, then a single
              > wafer switching between
              >ground and open will suffice. Generally with CMOS, an open input is
              >undefined, so it must
              >either be pulled up to Vcc or down to ground at all times. The only issue
              >in connecting to
              >ground is making sure the pin cannot be an output when it is connected to
              >ground.
              >
              >Dave - WB6DHW
              ><http://wb6dhw.com>
              >
              >
              >------------------------------------
              >
              >Yahoo! Groups Links
              >
              >
              >
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