RE: [tracker2] RE: Ok Now What?
- Wouldn't that mean putting +/- 9 volts on TTL inputs? Will the MAX232
> -----Original Message-----
> From: email@example.com
> [mailto:firstname.lastname@example.org] On Behalf Of Ian ZL1VFO
> Sent: Saturday, April 01, 2006 6:27 PM
> To: email@example.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
> 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.
> Ian ZL1VFO
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> Date: Sat, 1 Apr 2006 18:32:05 -0800Well, mine and a few other Hams I've done boards for have been running
> From: <scott@...>
> Subject: RE: Ok Now What?
> Wouldn't that mean putting +/- 9 volts on TTL inputs? Will the MAX232
> tolerate that?
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.
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