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Re: [softrock40] 12F683 Question

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  • Pete Smith
    Great, Jack, as always. Thanks! 73, Pete
    Message 1 of 13 , Jul 1, 2008
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      Great, Jack, as always. Thanks!

      73, Pete

      At 08:38 AM 7/1/2008, you wrote:
      >I should also add that any inexpensive NPN transistor can be used as a
      >switch with a Vsat around a couple tenths of a volt. Hence it is
      >possible to use the switch, a diode and a base current limiting resistor
      >to turn a 2N2222 or 2N4401 on/off with the PIC's input connected to the
      >NPN's collector. (Needs a pull-up resistor, of course.) Or, a 2N7000
      >MOSFET can be used if you don't like bipolars. As long as the pull up
      >resistor isn't too large, the 2N7000 will also give you a low voltage of
      >a couple tenths.
      >
      >Jack
      >
      >
      >Jack Smith wrote:
      > >
      > > Yes, that is how the data sheet is to be read.
      > >
      > > As far as using diode steering or diode logic, a couple points. First is
      > > that 0.7 volt drop is the common assumption for a diode drop. It's far
      > > less than this for low current. Check the typical 1N4148 data sheet, or,
      > > better yet, set up a quick test with a diode, a 10K resistor, a variable
      > > DC power supply, a pair of digital meters and graph Vf vs If.
      > >
      > > For a lower drop, a Schottky diode such as a 1N5711 is preferable over a
      > > Germanium. However, a similar Vf versus If plot will be informative.
      > >
      > > I wrote about diode Vf versus If at
      > > http://www.cliftonlaboratories.com/diode_vf_vs_if.htm
      > > <http://www.cliftonlaboratories.com/diode_vf_vs_if.htm> but it will stick
      > > with you more if you also make the Vf versus If measurements yourself.
      > >
      > > The 0.15 Vdd threshold is for TTL-compatible inputs. I have not gone
      > > through the 12F683 data sheet, but some (many) PICs have some ports with
      > > Schmitt type inputs which have a different threshold. Table 15-5 implies
      > > that some 12F683 inputs have Schmitt construction with Vl = 0.2 Vdd.
      > >
      > > It's also likely that there is some margin in Table 15-5's values. For a
      > > one-off project, some people will accept operation outside the data
      > > sheet values, if the configuration works. You might try it and see what
      > > happens.
      > >
      > > Jack
      > >
      > > Pete Smith wrote:
      > > >
      > > > It appears from that table (which I had missed before) that if Vdd
      > > is 3.3
      > > > volts, then the maximum for a logic low is .15 * 3.3v, and .7 volts
      > > > will be
      > > > too high. Am I reading the table correctly?
      > > >
      > > > Would it be feasible to use germanium steering diodes instead, with a
      > > > forward voltage drop of ~.3 volts, or should I just go to plan B and
      > > > use a
      > > > rotary binary encoder? I'd prefer not to, because mMy objective in
      > > > this is
      > > > to select the 6 contest bands using a single rotary switch (2P6T) to
      > > > control the oscillator and bpf selection.
      > > >
      > > > 73, Pete
      > > >
      > > > At 07:43 AM 7/1/2008, Jack Smith wrote:
      > > > >Table 15-5 in the 12F683 data sheet.
      > > > >
      > > > >Jack
      > > > >
      > > > >
      > > > >Pete Smith 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.
      > > > > >
      > > >
      > > >
      > >
      > >
      >
      >------------------------------------
      >
      >Yahoo! Groups Links
      >
      >
      >
    • 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 2 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 3 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 4 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 5 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 6 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 7 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 8 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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