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Author Topic: EM-401 GPS Engine  (Read 4328 times)

cabala

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EM-401 GPS Engine
« on: December 06, 2008, 07:39:02 pm »

Hi, I currently have the EM-401 engine board which is relatively similiar to the EM-406 board. At least in the sense of communicating with it. I am currently trying to use the demo board and am having difficulties understanding how to get it to talk.

What is the board's default communication settings? Again I have the EM-401 which appears to be out of date and uses the SiRF II not III. In the datasheet it says the default command settings are 4800,n,8,1. Does this mean that it is defaulted to NMEA or do I still need to send the Switch to NMEA message in SiRF protocol first?

Thanks for any help, because this is slightly confusing and I can't seem to find help anyhere else.
« Last Edit: December 08, 2008, 02:59:26 pm by USG_TECH7 »
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USG_TECH7

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Re: EM-401 GPS Engine
« Reply #1 on: December 08, 2008, 01:05:37 pm »

Welcome to the forums Cabala!!!
.
Yes, that is exactly what it means. The unit is set for NMEA protocol communication by default. Therefore, there is no need to switch the protocol.  ;)
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cabala

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Re: EM-401 GPS Engine
« Reply #2 on: December 08, 2008, 03:38:36 pm »

Wow, I'm amazed at the ease of use for these modules. I wired it up to output through a RS232 Line driver and then to hyperterminal and just watched all the beautiful NMEA messages come spitting out. Here is the problem though. When I first turned it on I was inside and after about 3 minutes I realized it wasn't going to acquire any sattelites indoors so took it to my porch. After booting up about 45 seconds later it locked a signal and the LAT/LONG fields and everything started updating. I check with my cell phone and it was almost exact.

Well, I decided to put the project down for the night and return tommorow and worry about having my microcontroller deal with the data later, but when I returned and powered on the module, the outputs are different and after about 2 minutes it just locks up for some reason. Below is the last few messages coming from the module. The first time I powered it up, it only outputted the "OK to Send" output once in the begining, but now it does it every couple output sentances and like I said after about 2 minutes it just stops and I have to reset it to get it going again? What could have happened? Is it in some trickle power mode or something? I only tried to send it input commnads once, to turn off everything but the GPGGA output but it didn't seem tot accept it.

Thanks for the help, I thought I was so close to having everything working and now the GPS module just seems to quit on me. 

$GPRMC,000148.993,V,0000.0000,N,00000.0000,E,,,110104,,*1F
$PSRF150,1,*12
$PSRF150,1,*12
$GPGGA,000149.993,0000.0000,N,00000.0000,E,0,00,50.0,0.0,M,0.0,M,0.0,0000*79
$PSRF150,0,*13
$GPGSA,A,1,,,,,,,,,,,,,50.0,50.0,50.0*05
$GPRMC,000149.993,V,0000.0000,N,00000.0000,E,,,110104,,*1E
$PSRF150,0,*13
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cabala

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Re: EM-401 GPS Engine
« Reply #3 on: December 08, 2008, 06:34:01 pm »

Also, I can't seem to get the engine board to accept an input command either. I am transmitting at 4800,n,8,1 just like the board and I even used my hyperterminal to make sure the messages are transmitting correctly. I'm not sure why. Ultimately, I would like to disable every message but the GLL output every 10 seconds or so. According to the NMEA protocol user guide a message to disable GSA for example would look like this:

"$PSRF103,02,00,00,01*26\r\n"  ---> This is the message I send without the quotes of course. I calculated the checksum like the examples in the guide (XORing everything inside the $ and *. I also noticed that the checksum value of *12 (from the above output) which is being sent by the receiver does not coincide with the example in the protocol guide which is exactly the same as what the board is outputting. Why are these different?

Thanks again, I would really like to see this work. 
« Last Edit: December 08, 2008, 06:36:26 pm by cabala »
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