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[aprssig] RS-232 to GPIO/TTL

Jason Winningham jdw at eng.uah.edu
Thu Feb 22 22:30:57 UTC 2007

On Feb 22, 2007, at 4:08 PM, M J wrote:

> I've decided to try to build my own TNC and embed a Garmin GPS15M  
> into it!  Does anyone know of a source for an existing board (cheap  
> and small) that will convert RS-232 (from the Garmin) to GPIO/TTL  
> (on the MLB)?

What's an MLB?

The specs on the 15H says it's compatible with TTL voltages, but has  
rs232 levels.  This basically means you need a TTL inverter (both  
directions, if you hook up TX to the GPS).

If the device was true RS232, you'd want to use a MAX232 (or similar)  
RS232 transceiver.

You can also look at GPS engines (Sparkfun.com has several) that have  
TTL interfaces, so no TTl/RS232 conversion is required.

> If I can get them connected, then I'll need to learn how to create  
> a software based UART schema...

There are examples out there.  Or, you can just get another hardware  
UART if your microcontroller only has one.  I've got some SPI- 
interfaced UARTs that I haven't had a chance to hook up yet, but they  
look good on paper.

The arduino (http://arduino.cc/, Atmel based) has a hardware UART and  
a library for software UARTs.  Seems just a bit tight on RAM for some  
applications (2k), but I really like the platform.  Oh, and it's  
cheap (you mentioned you're a student. :)


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