Joe Della Barba joe at dellabarba.com
Sat Feb 5 20:54:58 EST 2011

Thanks for the help everyone.
I looked up some NMEA specs and marine devices are supposed to have
opto-isolators on the input side. The VHF must have one, because it reads
the data fine.
So I need one of those for the TT2 maybe? Is there a circuit around for
I looked up this device you mentioned
Do these invert the GPS output? AFAIK, I don't need it inverted, just more

Joe Della Barba
joe at dellabarba.com

73 de N3HGB-5

-----Original Message-----
From: Jason KG4WSV [mailto:kg4wsv at gmail.com] 
Sent: Saturday, February 05, 2011 8:28 PM
To: TAPR APRS Mailing List
Cc: joe at dellabarba.com
Subject: Re: [aprssig] NMEA ISSUE HELP

On Sat, Feb 5, 2011 at 6:54 PM, Andrew Rich <vk4tec at tech-software.net>
> Given that the GPS is TTL type logic,

No, it is not TTL logic, it's TTL voltages.  TTL signals are inverted
compared to RS232.  A logic high is 5V TTL but -12V RS232.

> can u suggest a TTL style chip apart
> from optos, that might be able to provide say 8 streams of "repeated" 
> NMEA TTL data ?

I used a MAX237 and managed to pass 3 extra TX-only copies of the
rs232 data with a single IC (plus a few caps).


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