daemondust:
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.
I’m just a super paranoid person…anything i haven’t done in the past is questionable lol
The RX input is probabaly a high impedance input to an IC. Most likely it's just the gate of a fet, so when the device is started there could be a very small amount of current to charge the gate capacitor on that fet, and then current should drop to ~0. (I think actual current would normally be in the pico amp range or less, but I'd have to check some notes I have which are halfway across the globe from me). Thus a resistor divider should work just fine. I expect you can even use ones in the M range, if that extra ma is that essential to save.daemondust:
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.
The reason resistor dividers are not always the ideal solution is because they are most accurate when current draw is 0. But again, current draw here should be so minor that it should be, essentially, 0.
One thing though - you can probabaly get away with connecting the rx pin to a 3.3v line. I believe the whole EM-406 module runs off of 3.3V, so that should not be a problem at all, and it is unclear to me why they would reccomend 3.5V.
http://computing.unn.ac.uk/staff/CGWH1/ … e%20Manual’ or do a search on SIRF GPS reference Manual. Something should pop right up.
Is the Sirf GPS Reference protocol. Section 1.2.6 tells you how to change the nmea sentences and baud rate via normal uart mode versus binary protocol.
Level shifting is fine and works. I still recommend using the $.08 transistor for receiving incoming nmea messages. A better description of how this works can be found at: http://www.picbasic.org/forum/showthread.php?t=6153
if it’s a 3.3V chip… why does it output 2.85V?
ohararp:
http://computing.unn.ac.uk/staff/CGWH1/ … e%20Manual’ or do a search on SIRF GPS reference Manual. Something should pop right up.Is the Sirf GPS Reference protocol. Section 1.2.6 tells you how to change the nmea sentences and baud rate via normal uart mode versus binary protocol.
Level shifting is fine and works. I still recommend using the $.08 transistor for receiving incoming nmea messages. A better description of how this works can be found at: http://www.picbasic.org/forum/showthread.php?t=6153
thanks… yea i’m gonna go the transistor route for level shifting…
and I’m gonna use na adjustable regulator to pull the RX pin to 3.5V… i’m going to maek a board for the GPS… so board space isn’t as big an issue… it still is… but i cna add more stuff… i’m gonan go with the adjustable 3.5V regulator because then there is no question it will work… i don’t want to screw up my grade in the class…
when you pull the EM406 out of the box does it send data in ASCII?? i don’t understand… what is binary mode?? i’m confused… and what is NME protocol mode? i’m confused about the data format… the datasheet isn’t too clear on that
When you power it up for the first time it starts sending NMEA data at 4800 bps. That is, you get messages like
$GPGGA,112434.000,3910.6119,N,08633.1331,W,1,08,1.3,274.4,M,-33.6,M,,0000*61
http://www.usglobalsat.com/downloads/NMEA_commands.pdf describes the NMEA messages you may see, and those you may send to the receiver.
SiRF binary mode is when you have the receiver use SiRF’s proprietary data format. This is described in http://www.usglobalsat.com/downloads/Si … otocol.pdf . This allows more flexibility (NMEA only describes certain messages, SiRF binary allows for more) at the cost of compatability.
I have left the pin floating or I direct connect it to the uPic for processing if I need it. THis might be a better option for you.
You should consider purchasing the SFE rs232 → em406 board. You can get a lot done using hyperterminal and talking to the em406. You can also use the afforementioned sirf star demo as well.
ohararp:
I have left the pin floating or I direct connect it to the uPic for processing if I need it. THis might be a better option for you.You should consider purchasing the SFE rs232 → em406 board. You can get a lot done using hyperterminal and talking to the em406. You can also use the afforementioned sirf star demo as well.
yea i’m going to buy that board…
i was looking into the USB version though… because then i can use it with my laptops… which is what i wil lbe using for this project…
unless there’s a reason i shouldn’t??
i was talk that the USB version emulates a RS232 so you can connect to hyperterminal and see the mesages…
what do you thinmk?>
good option because you will not need the 5v power supply as well an rs232 cable. Drivers can be an issue sometime but should not be a problem.
So if i go with the USB version will i still be able to change the baud rate… i mean… looking at the documentation it sounds like you cna’t…
it just say’s the the USB board runs at 4800 baud…
Take a look at the reference manual. By sending the EM406 “commands” you can change a bunch of things (uP or PC). Additionally, if you use the sirfdemo.exe program you can change even more things using the pull down menus that implement the binary protocol. Using the usb dev card you will be all set.
ohararp:
Take a look at the reference manual. By sending the EM406 “commands” you can change a bunch of things (uP or PC). Additionally, if you use the sirfdemo.exe program you can change even more things using the pull down menus that implement the binary protocol. Using the usb dev card you will be all set.
i was looking at the board… it has external interface pins… maybe i don’t have to design a board for the EM406… and i can just use that board right into my project… the only thing is… i need some extra hardware that i’m gonna puton htatsecond board… so i might just make a board for hte EM406 anyway…
hehe but thanks
I would definitely consider using the board in “development” work and then when you know your connections are correct and your code works then go ahead and make a dedicated pcb.