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Re: [softrock40] 12F683 Question

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  • k5nwa
    ... Not sure,but use a 1N34A Germanium diodes and you get .3 Volt Drop, a second alternative is a Schotty diode. Cecil K5NWA www.softrockradio.org
    Message 1 of 13 , Jul 1, 2008
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      At 06:05 AM 7/1/2008, you 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
      >

      Not sure,but use a 1N34A Germanium diodes and you get .3 Volt Drop, a
      second alternative is a Schotty diode.



      Cecil
      K5NWA
      www.softrockradio.org www.qrpradio.com

      "Blessed are the cracked, for they shall let in the light."
    • jeffthom99
      ... ground ... at .7 ... sheet of ... 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
      Message 2 of 13 , Jul 1, 2008
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        --- 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
      • Mike Young
        Why the diode? ... From: Pete Smith To: Sent: Tuesday, July 01, 2008 6:05 AM Subject: [softrock40] 12F683
        Message 3 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 4 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 5 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 6 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 7 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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