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RE: Ok Now What?

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  • Ian ZL1VFO
    Message 1 of 15 , Apr 1, 2006
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      > Message: 15
      > Date: Fri, 31 Mar 2006 20:49:50 -0800
      > From: <scott@...>
      > Subject: RE: Ok Now What?
      >
      > Before the MAX232, actually.. it'll most likely be a 2N3904 with a pull up
      > to 5 volts, so that an input on the base pulls it low - same as the RX side
      > of the tracker itself. I'll come up with a schematic after I get the shells
      > and see what will fit.

      > Scott

      Well, since the MAX232 has 2 line drivers and 2 line receivers, all 4
      of which are inverters, couldn't you just use the 'spare' inverters
      to re-invert back to normal? I've done just that on my home made
      TinyTrak board - it's been working reliably for several years now.

      Let's see, looking at my notes for what I did, <rummage, rummage> the
      uController TxD line joined to the MAX232's pin11 (T1in),
      pin14 (T1out) to pin10 (T2in), pin7 (T2out) to the DB9 TxD.

      Going back the other way, DB9 RxD to pin8 (R2in),
      pin9 (R2out) to pin13 (R1in), Pin12 (R1out) back to RxD on the
      uController.

      I also have 2 rows of 4 jumper pins connected to this circuit, so I
      could jumper them either as 2 inverters in series (no inversion), or 2
      inverters in parallel (inversion) for each direction, depending on
      what was required at the time.

      I may be able to draw it out & post it in the files section, if
      anyone's interested.

      73,
      Ian ZL1VFO



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    • scott@opentrac.org
      Wouldn t that mean putting +/- 9 volts on TTL inputs? Will the MAX232 tolerate that? Scott
      Message 2 of 15 , Apr 1, 2006
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        Wouldn't that mean putting +/- 9 volts on TTL inputs? Will the MAX232
        tolerate that?

        Scott

        > -----Original Message-----
        > From: tracker2@yahoogroups.com
        > [mailto:tracker2@yahoogroups.com] On Behalf Of Ian ZL1VFO
        > Sent: Saturday, April 01, 2006 6:27 PM
        > To: tracker2@yahoogroups.com
        > Subject: [tracker2] RE: Ok Now What?
        >
        > > Message: 15
        > > Date: Fri, 31 Mar 2006 20:49:50 -0800
        > > From: <scott@...>
        > > Subject: RE: Ok Now What?
        > >
        > > Before the MAX232, actually.. it'll most likely be a 2N3904
        > with a pull up
        > > to 5 volts, so that an input on the base pulls it low -
        > same as the RX side
        > > of the tracker itself. I'll come up with a schematic after
        > I get the shells
        > > and see what will fit.
        >
        > > Scott
        >
        > Well, since the MAX232 has 2 line drivers and 2 line receivers, all 4
        > of which are inverters, couldn't you just use the 'spare' inverters
        > to re-invert back to normal? I've done just that on my home made
        > TinyTrak board - it's been working reliably for several years now.
        >
        > Let's see, looking at my notes for what I did, <rummage, rummage> the
        > uController TxD line joined to the MAX232's pin11 (T1in),
        > pin14 (T1out) to pin10 (T2in), pin7 (T2out) to the DB9 TxD.
        >
        > Going back the other way, DB9 RxD to pin8 (R2in),
        > pin9 (R2out) to pin13 (R1in), Pin12 (R1out) back to RxD on the
        > uController.
        >
        > I also have 2 rows of 4 jumper pins connected to this circuit, so I
        > could jumper them either as 2 inverters in series (no inversion), or 2
        > inverters in parallel (inversion) for each direction, depending on
        > what was required at the time.
        >
        > I may be able to draw it out & post it in the files section, if
        > anyone's interested.
        >
        > 73,
        > Ian ZL1VFO
        >
        >
        >
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      • Ian ZL1VFO
        Message 3 of 15 , Apr 2, 2006
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          > Date: Sat, 1 Apr 2006 18:32:05 -0800
          > From: <scott@...>
          > Subject: RE: Ok Now What?

          > Wouldn't that mean putting +/- 9 volts on TTL inputs? Will the MAX232
          > tolerate that?

          > Scott

          Well, mine and a few other Hams I've done boards for have been running
          like that for a several years now, with no ill effects.

          I suppose adding (say) a 10k resistor between pin14 (T1out) & pin10
          (T2in) would reduce the amount of current flowing into pin 10 and
          onwards through whatever input protection diodes there are inside the
          MAX232. If I get a bit of time tommorow I might try various
          resistances and see what effect it has on the voltages applied to
          pin10 (T2in) while watching it with a 'scope.

          Ian ZL1VFO





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