[aprssig] GPS GT-320FW(AS)

Jason KG4WSV kg4wsv at gmail.com
Tue Apr 23 09:03:00 CDT 2013


On Tue, Apr 23, 2013 at 7:27 AM, Dave B <dave at g8kbv.demon.co.uk> wrote:
> Come on guys, this isn't rocket scienct....
>
> Has everyone forgotten how to think through an issue, or search online?

C'mon Dave, we're just speculating in the absence of information.  One
the one hand, we've got a rather inadequate datasheet from the GPS
manufacturer, and on the other we don't even know what Andrew is
interfacing with.

As to your "google", the only really useful information will come from
the datasheets of the devices in question; everything else is
guessing.  And as I tell my daughter, any idiot can put up a web page,
and many do.  I've even got one. :)

>  You can use just one NPN transistor (and some passives) for the
> incoming '232 to TTL, and similarly, one PNP device (and a -ve rail) for
> the outgoing "driver".

I personally despise this transistor trick.  I find it frequently
unreliable, especially if you're connecting two devices that both use
the trick.  Using a MAX232 (or equivalent) is not that hard or
expensive, and it always works.  I've fabricated some little PCBs that
have a DB9 on one end and TTL level tx/rx/vcc/gnd on the other end,
and have them lying around for this sort of project.  They're a few $
each but can save time and a ton of frustration.

Besides that, transistors aren't usually rated for exposure to the
outside world; I killed a couple 2N7000 transistors on OpenTrackers
before Scott switched to a special 2n7000 with some ESD protection
built in.  The MAX232 type devices include ESD protection since it is
designed to interface to the outside world.

> Next question, who remembers what U A R T actually stands for?

*yawn*  universal asynchronous receiver transmitter


As to the previous "USART" question, at least on some ATmega
microcontrollers they have a chunk of logic for communications that
may be used for UART, SPI, etc, depending on how it's configured.
IIRC, one of the Xmega lines have multiple USARTs that can be used for
either RS232 type or SPI (and maybe other types) communication.

-Jason
kg4wsv


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