Re: [gpsd-dev] SemPiTernal - Bounding PPS uncertainty

[Gary E. Miller]

Yo Phil!

On Fri, 22 Apr 2016 21:19:54 -0400
Phil Salkie <address@hidden> wrote:

> On Fri, Apr 22, 2016 at 6:35 PM, Gary E. Miller <address@hidden>
> wrote:
> > Yo Hal!
> >
> > On Fri, 22 Apr 2016 06:07:40 -0700
> > Hal Murray <address@hidden> wrote:
> >  
> >> address@hidden said:  
> >> > If you recall, we had an issue with connecting the Garmin GPS
> >> > hockey puck to a serial port - even after converting the 0 to
> >> > 5VDC data lines to RS-232's -10 to +10VDC, we still couldn't
> >> > read it,  
> >
> > RS-232 is +/- 12V.  
> 
> Technically, the spec allows anything between -3 and -25 on the down
> (mark) side, and anything between +3 and +25 on the up (space) side -
> 0VDC is in the undefined zone, which is why some receivers will see it
> as a mark, and some see it as a space

Well, technically, according to the actual standard, the output must be
between -5V and -15V for mark and +5V and +15V for space.  The input can
be between -3V and -25V or +3V and +25V.  The difference is to allow for
cable resistive drop and common mode noise and ground loop.

And technically the max speed of TIA-232 is 20kbps.  Not very useful in
today's world.

Your talking to one of the few suckers that bought the standard years ago.
Sorta useless since no one ever followed the standard.

I always assume -12V/+12V since that was what IBM always used.  From
the same power supply as the HDDs.  Many of the classic RS-232 drivers,
like the TI SN75C185 are specified for -12V/+12V nominal.  Some like the
SN75185 for nominal -9V/+9V but usually driven at -12V/+12V.

Nowadays companies like Maxim sell chips that output down at -5V and 5V,
makes me shudder.

> that's why I put together the
> converter board (with the extra channel to provide the PPS, and the
> LED to see it pulsing.)

Maybe we should swap Eagle Cad files.  I designed the same thing as
you before I could buy them cheap.  I also added a mini-din connector,
with breakout pins, to work easily with Garmin's etc.

RGDS
GARY
---------------------------------------------------------------------------
Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703
        address@hidden  Tel:+1 541 382 8588

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