EM406 questions

GPS/GNSS Development Boards
1

Hi,

I’m new to this GPS thing…

anyway… i have a few questions

  1. I’m running a 5V micro contrller that can only hand 3V as minimum for logic high (I’m just gonna say 3.3V is the lowest)… the EM406 outputs 2.85 as logic high… what do you guys suggest I do in order to be able to shift voltages from 2.85V => 5V for reading the module and 5V=>2.85 for writting to it…

The data sheets on the EM406 aren’t very specific… WHen it starts up… what do i do?? do i have to configure it… do i have to send stuff to it?? what happens?

How do you gyus normally power the unit? I have a 5V regulator, but the GPS unit has it’s own regulator… as far as i know… it’s bad to chanin regulators… so what do you guys do?

2

hello?

Also, how do you guysgenerate 2.85V so that the shifter can output to the GPS unit…

so what i’m saying is, when you’re trying to go from 5V to 2.85V, how do you generate 2.85V to power the shifter…?

3

  1. You can use a circuit similar to what’s described in http://www.sparkfun.com/datasheets/Prot … ter-v2.pdf to shift the output. You could also use something like TI’s [sn74lvc4245, but it isn’t exactly what you need since it can only go one way at a time, and has more converters than you need.

  2. When it starts up it starts spitting out NMEA sentences. I think the default is to send a GGA, a GSA, and a RMC sentence every second, and to send a GSV every 5. By default it does this at 4800bps. You can use a program called [SiRFDemo to change what messages it sends out, how frequently, and at what speed.

  3. While it generally isn’t a good idea to chain regulators, it usually works fine. If you’re worried about connecting it to your 5v line, add a filter cap. next to the GPS module to reduce ripple.

  4. You could use anything from a resistor divider, to a zener diode acting as a shunt regulator, to a full linear or switching regulator. Unless you’re on limited battery power, a resistor divider should be fine. However, you may not need to generate a ~2.85v line at all.](http://www.gpspassion.com/forumsen/topic.asp?TOPIC_ID=25575)](http://focus.ti.com/lit/ds/symlink/sn74lvc4245a.pdf)

4

So are you saying, what i can do is… use the sirf software to set the speeds and messages i want… and then plug the board into the baord i’m making (I’m making a GPS tracking system… duh)… and it will automatically start sending out messages in the fashion i told it to with the program???

meaning… that, if i buy an eval board for the GPS module, and set what i want on the computer… i don’t have to program my micro controller to talk to the GPS… just read from it??

5

Yes, that’s what I’m saying. It keeps the settings you give it through power cycles.

6

Well why didn’t you saythat earlier!!!

7

RancidWannaRiot:
Well why didn’t you saythat earlier!!!

Sorry I wasn’t more specific. I guess I shouldn’t post before caffeine…

8

I’m just messing with you man… don’t worry…

Which Eval board do you recommend? the one with RS232 or the one with USB?? or does it not matter? which interface does the program work better with?

9

I think you’ll have to switch to SiRF Binary before you can change the NMEA messages sent, so you’ll want a board that can switch speeds at will. The SiRF Binary protocol defaults to 57600bps. Because of the price, I would probably go with the [RS232 Shifter SMD. If you have a 3.3v regulator that would be perfect. I don’t have any trouble running my EM-406 on that. Make sure you can supply enough current to the receiver. The datasheet says 70mA max, but I’m reading more like 90mA when running it off of 5v. I usually just run the whole thing off of my 3.3v line, and the receiver doesn’t seem to mind.

In SiRFDemo, you would go to “Action” → “Switch to SiRF Protocol”, then to “Action” → “Switch to NMEA Protocol”. That should pop up a box asking for how often you want messages to be sent, and at what baud rate.](http://www.sparkfun.com/commerce/product_info.php?products_id=449)

10

daemondust:
I think you’ll have to switch to SiRF Binary before you can change the NMEA messages sent, so you’ll want a board that can switch speeds at will. The SiRF Binary protocol defaults to 57600bps. Because of the price, I would probably go with the [RS232 Shifter SMD. If you have a 3.3v regulator that would be perfect. I don’t have any trouble running my EM-406 on that. Make sure you can supply enough current to the receiver. The datasheet says 70mA max, but I’m reading more like 90mA when running it off of 5v. I usually just run the whole thing off of my 3.3v line, and the receiver doesn’t seem to mind.

In SiRFDemo, you would go to “Action” → “Switch to SiRF Protocol”, then to “Action” → “Switch to NMEA Protocol”. That should pop up a box asking for how often you want messages to be sent, and at what baud rate.[/quote]

You lost me there…

Okay… why would i need that RS232 device? What about this http://www.sparkfun.com/commerce/produc … cts_id=653

can’t i just use that???

then use the software to change into the NMEA protocol???](http://www.sparkfun.com/commerce/product_info.php?products_id=449)

11

Yes, that will work fine. I completely forgot that SFE has that.

12

daemondust:
Yes, that will work fine. I completely forgot that SFE has that.

LOL… hehe well thanks a lot for answering my questions… i’m still dealing with the lvel shifting though… the problem with the circutyou showed me… is that the output gets inveted…

RS232 is inverted… that is -12V is logic high and 12V is logic low… the transistors are basically a resistive load inverter… so that’s how you switch back to 5V = 1, V= 0

but i thin i figured out a circuit that won’t invert…

13

Where can i get the software that goes with this unit?

14

http://www.falcom.de/uploads/media/SiRF … _v3.81.zip

15

Thanks!

also… since I don’t have to write to the GPS unit when i hook it up to my micro controller…

what should i do with the RX pin on the GPS unit?? i sholdn’t leave it floating since it’s an input…

should i pull it up or pull it down?

thanks

16

The [newer version of the datasheet says to pull the RX pin to 3.5v through a resistor if you don’t use it.](http://www.usglobalsat.com/downloads/engineboards/EM406.pdf)

17

daemondust:
The [newer version of the datasheet says to pull the RX pin to 3.5v through a resistor if you don’t use it.[/quote]

damn it… to 3.5V?? bleh it should at least be 3.3V damn… what kind of voltage is 3.5… man soo many issues](http://www.usglobalsat.com/downloads/engineboards/EM406.pdf)

18

There’re a lot of odd requirements for this module. From what I’ve found, it was specifically made for one device, and they later decided to sell it as an OEM module.

If I were doing this I would use a resistor divider. If you used about a 1.5 kohm pullup to 5v and a 3.5 kohm pulldown to ground you would get the right voltage at the RX pin and only waste 1mA.

You can search google for “resistor divider calculator” to find several pages that will find the resistor values you can use.

19

daemondust:
There’re a lot of odd requirements for this module. From what I’ve found, it was specifically made for one device, and they later decided to sell it as an OEM module.

If I were doing this I would use a resistor divider. If you used about a 1.5 kohm pullup to 5v and a 3.5 kohm pulldown to ground you would get the right voltage at the RX pin and only waste 1mA.

You can search google for “resistor divider calculator” to find several pages that will find the resistor values you can use.

I thought about that… but is that proper??? there’s no funny business with that??

I’m gonna guess no current is going to go into the RX input correct?

i found a 3.V regulator…but it’s only 20mA… that’s a bit too small in my opinion…

I’m just worried that using a resistor divider will mess things up??? or do you think it woudl be fine??

20

I don’t have much of a formal electrical background, but why wouldn’t it work? There’s almost no current flowing into the RX pin.

As far as I know, the reason most people avoid resister dividers is because they’re horribly inefficient if you’re drawing any appreciable current.

Someone else here can speak up if I’m wrong.