[aprssig] NMEA ISSUE HELP

[Joe Della Barba]

Thanks all for the help.
I got a marine GPS, a Garmin 17-N, and hooked it up. The output drives the
VHF, TT2, and computer just fine. Believe it or not, it was only $5 on Ebay
and had never been used!
:)
:) 


Joe Della Barba
joe at dellabarba.com

-----Original Message-----
From: Jason KG4WSV [mailto:kg4wsv at gmail.com] 
Sent: Saturday, February 05, 2011 9:39 PM
To: joe at dellabarba.com; TAPR APRS Mailing List
Subject: Re: [aprssig] NMEA ISSUE HELP

On Sat, Feb 5, 2011 at 7:54 PM, Joe Della Barba <joe at dellabarba.com> wrote:
> I looked up this device you mentioned
> (http://www.datasheetcatalog.org/datasheet/maxim/MAX220-MAX249.pdf)
> Do these invert the GPS output? AFAIK, I don't need it inverted, just 
> more voltage.

an RS232 transceiver both inverts the logic and changes the voltage.
I feed the RS232 into the MAX237, fan out on the TTL side, and go back to
RS232 for the extra copies.  A schematic is here:

http://www.eng.uah.edu/~jdw/avr/MAX237_GPS_splitter.png

This circuit includes a regulator and a jumper (R1) to feed 5V to the GPS18.

One up side of this arrangement is a non-standard RS232 implementation like
the GPS18 comes out of the splitter meeting spec.

-Jason
kg4wsv