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Electronics => Electronics => Topic started by: Aberg098 on August 03, 2010, 09:39:52 AM

Title: GPS wiring help
Post by: Aberg098 on August 03, 2010, 09:39:52 AM
Hello all,

Although I admit to being a complete newbie at this, I need to tap into the wisdom of the SoR forums.

I'm interfacing an EM-408 GPS from sparkfun into an Axon2. Here's the datasheet I'm referring to:
http://www.usglobalsat.com/download/47/em408_ug.pdf (http://www.usglobalsat.com/download/47/em408_ug.pdf)

More specifically this part about the Rx pin (on page 5):

RX: This is the main receive channel for receiving software commands to the engine board from SiRfDemo software or from user-written software. (NOTE: When not in use this pin must be kept “HIGH” for operation. From Vcc connect a 470 Ohm resistor in series with a 3.2v Zener diode to Ground. Then, connect the Rx input to Zener’s cathode to pull the input “HIGH”.)

So I gather that I need a diode and a resistor. I think the correct diode to use is NTE 5005SM, since this is a 3.3V circuit. Where I'm not clear is what pin represents the anode and the cathode...

Title: Re: GPS wiring help
Post by: Razor Concepts on August 03, 2010, 10:20:03 AM
The side with the stripe is the anode
Title: Re: GPS wiring help
Post by: waltr on August 03, 2010, 11:53:12 AM
Quote
The side with the stripe is the anode
Did you try looking it up in Wiki?
http://en.wikipedia.org/wiki/Zener_diode (http://en.wikipedia.org/wiki/Zener_diode)

The stripe is the Cathode!
Title: Re: GPS wiring help
Post by: Razor Concepts on August 03, 2010, 11:58:41 AM
Quote
The side with the stripe is the anode
Did you try looking it up in Wiki?
http://en.wikipedia.org/wiki/Zener_diode (http://en.wikipedia.org/wiki/Zener_diode)

The stripe is the Cathode!


DARN! Hope you didn't fry anything  :-X
Title: Re: GPS wiring help
Post by: Aberg098 on August 03, 2010, 01:07:57 PM
Luckily I didn't fry anything, as I haven't received the diode yet!

That being said, somebody pointed out to me the following comment from the sparkfun product page:

by SteveMajor   +1.8 |   Feb 19, 2009 at  2:59pm   0
This device works beautifully. We hooked it up--indoors with no window for giggles--and it immediately got a 3d fix from 5 satellites with the on-board patch antenna alone. It should work even better outside. Some things not in the data sheet--tie both enable and RX to 3.3 V and the output is defaulted to 4800 baud 8,n,1. Our senior design group is very happy with this module. Another group is also having success with the EM-406A module.

So what should I do about this? try the diode thing, or just tie E/D to Rx to 3.3V? I really just need the gps to spit out data, nothing fancy.