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RE: [tracker2] RE: Ok Now What?

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  • scott@opentrac.org
    Wouldn t that mean putting +/- 9 volts on TTL inputs? Will the MAX232 tolerate that? Scott
    Message 1 of 15 , Apr 1 6:32 PM
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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 2 of 15 , Apr 2 4:27 AM
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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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