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[spork]

Can anyone point me to a list of the command strings accepted by the BR-355 for setting baud rate, enabling and disabling various NMEA sentences, etc.?

Sorry if this is a dumb question - and thanks in advance.

[spork]

I ended up finding the answer through a Google search (after learning what to search for through this forum).  I'll post it here for others:

http://www.gpsinformation.org/dale/nmea.htm

The SiRF line of chips support several input sentences that permit the user to customize the way the chip behaves. In addition SiRF has a binary protocol that is even more powerful permitting different implementations to behave entirely differently. However, most applications do not attempt to customize the behavior so a user will need to make sure that the any customization is compatible with the application they are planning to use. There are 5 input sentences defined that begin with $PSRF which is followed by three digits. Each sentence takes a fix amount of input fields which must exist, no null fields, and is terminated with the standard CR/LF sequence. The checksum is required.

The sentences 100 and 102 set the serial ports. 100 sets the main port A while 102 sets the DGPS input port B. 100 has an extra field that can be used to switch the interface to binary mode. Binary mode requires 8 bits, 1 stop bit, no parity. There is a command in binary mode that will switch the interface back to NMEA. Do not use the NMEA command to switch to binary mode unless you have the ability to switch it back. You could render your gps inoperative.

 $PSRF100,0,9600,8,1,0*0C
 $PSRF102,9600,8,1,0*3C

where
   $PSRF100
   0          0=SiRF, 1=NMEA  - This is where the protocol is changed.
   9600       b/s rate 4800, 9600, 19200, 38400
   8          7, 8 Databits
   1          0, 1 Stopbits
   0          0=none, 1=odd, 2=even Parity
   *0C        checksum
The sentences 101 and 104 can be used to initialize values to be used by the gps. Supplying these values can shorten the initial lock time. If the clock offset is set to 0 then an internal default will be used. Sentence 101 supplies data in the internal ECEF (Earth centered, Earth Fixed) format in meters while sentence 104 supplies the data in the traditional Lat / Lon format.

 $PSRF101,-2686700,-4304200,3851624,95000,497260,921,12,3*22
 $PSRF104,37.3875111,-121.97232,0,95000,237759,922,12,3*3A

where
   $PSRF104
   37.3875111 Latitude in degrees
   -121.97232 Longitude in degrees
   0          Ellipsoid Altitude in meters
   95000      Clock offset
   237759     GPS Time of Week in seconds
   922        GPS Week Number
   12         Channel count (1 to 12)
   3          Reset config where
              1 = warm start, ephemeris valid
              2 = clear ephemeris, warm start (First Fix)
              3 = initialize with data, clear ephemeris
              4 = cold start, clear all data
              8 = cold start, set factory defaults
   *3A        checksum
The sentence 103 is used to control which NMEA sentences are to be sent and how often. Each sentence type is controlled individually. If the query bit is set then the gps responds by sending this message in the next second no matter what the rate is set to. Note that if trickle power is in use (can only be set in binary mode) then the actual update rate will be the selected update rate times the trickle rate which could mean that the data will be sent less frequently than was set here.

 $PSRF103,05,00,01,01*20

where
   $PSRF103
   05         00=GGA
              01=GLL
              02=GSA
              03=GSV
              04=RMC
              05=VTG
   00         mode, 0=set rate, 1=query
   01         rate in seconds, 0-255
   01         checksum 0=no, 1=yes
   *20        checksum
The 105 sentence controls a debug mode which causes the gps to report any errors it finds with the input data. $PSRF105,1*3E would turn debug on while $PSRF105,0*3F would turn it off.

[GS_TECH01]

Hello spork,

Welcome to the forums! Hope you enjoy looking around.

Regarding the NMEA commands to set the baud rate, enable and disable the NMEA sentences, etc., you could take a look at this NMEA commands document as well: http://www.usglobalsat.com/store/downloads/NMEA_commands.pdf

Let me know if you have any questions.

[spork]

Regarding the NMEA commands to set the baud rate, enable and disable the NMEA sentences, etc., you could take a look at this NMEA commands document as well: http://www.usglobalsat.com/store/downloads/NMEA_commands.pdf

Thanks very much.  That's a great reference.

I do have another question if I may... I've currently interfaced a BU-353 to an Arduino board by bypassing the serial-to-USB chip internally.  I get the sense that the BR355 does this differently.  I'm using a 3.3V signal level with the 353.  Does the 355 have legal RS-232 protocol and signal level?

Thanks again.

[GS_TECH01]

What do you mean by legal RS-232 protocol and signal level? If you mean that you want to connect the BR-355 through an RS-232 port, then, you have to purchase an RS-232 Cable Set. More info about that can be found here: http://www.usglobalsat.com/forum/index.php?topic=3506.0

If not, can you please explain further and provide more details?

[spork]

What do you mean by legal RS-232 protocol and signal level? If you mean that you want to connect the BR-355 through an RS-232 port, then, you have to purchase an RS-232 Cable Set. More info about that can be found here: http://www.usglobalsat.com/forum/index.php?topic=3506.0

If not, can you please explain further and provide more details?

I'm not looking to plug it into a "real" computer.  For that I'll use the BU-353 (USB version).  I just need to know the signal levels at the GPS receiver to properly interface it with my Arduino.  My converted BU-353 appears to use 0-3.3V signals.  This works as input to my 5V Arduino.  I imagine I'd use a simple voltage divider to send commands to the BU-353 (so as not to put 5V into a 3.3V device). 

I'm wondering if the BR-355 has the same signal level and protocol as the BU-353 (i.e. 0-3.3V) or has a built-in RS-232 converter so the signal levels work with a typical computer serial port.

Looking at it another way - does the cable you're describing do any signal conditioning?

Thanks again.

[GS_TECH01]

Thanks for the info. Just a few questions:

Regarding the BU-353, how were you able make it operate within the 0 - 3.3V? Since this device normally requires 5V for it to power on (http://www.usglobalsat.com/store/download/62/bu353_ds_ug.pdf).
Can you also provide links to datasheets, reference, and other relevant materials about the Arduino board?

The BU-353 and BR-355 uses the same NMEA protocol (http://www.usglobalsat.com/store/download/57/br355_ds_ug.pdf). Their main difference is the connection type: BU-353 is USB and BR-355 is serial. But, they have the similar performance and works the same. However, the BR-355 doesn't have a built-in RS-232 converter. To be able to connect it via a serial port, you can use the RS232 Cable Set (http://www.usglobalsat.com/p-228-br305-rs232-rs232-cable-set.aspx#images/product/large/228.jpg) and the PS2 male connections is used for power.

Let me know if that answers your questions.

[spork]

Regarding the BU-353, how were you able make it operate within the 0 - 3.3V? Since this device normally requires 5V for it to power on

I do provide 5V supply to power it.  But I believe it's internally regulated to 3.3V - at least where I tapped into it at the serial-to-USB conversion IC.

Can you also provide links to datasheets, reference, and other relevant materials about the Arduino board?

Sure - but I don't think there's anything special about that end of it.  I'd just like to confirm the voltage levels of the BU-353 serial.  Hopefully, this will tell you everything you need to know about the Arduino: http://arduino.cc/en/Main/ArduinoBoardUno/  But I'll be happy to provide whatever other data you might need.

The BU-353 and BR-355 uses the same NMEA protocol (http://www.usglobalsat.com/store/download/57/br355_ds_ug.pdf).

Excellent.  I suspected so.

the BR-355 doesn't have a built-in RS-232 converter. To be able to connect it via a serial port, you can use the RS232 Cable Set (http://www.usglobalsat.com/p-228-br305-rs232-rs232-cable-set.aspx#images/product/large/228.jpg) and the PS2 male connections is used for power.

And this is getting to the crux of the matter.  I'm wondering if that cable set is performing the RS-232 conversion.  I'd rather not perform the conversion to RS-232 voltage levels simply to convert them back to logic levels for the Arduino.  I was originally doing something similar with the USB version.  The 353 is nominally a serial device, but its communications are converted internally to USB.  I then use a USB host converted on the Arduino side to convert it back to serial.  This proved to be a very fragile solution.  My current solution (having tapped into the serial signal within the 353) seems simple and robust.  But it's WAY too hard to solder wires on those tiny surface mount pins.  The perfect solution would seem to be for me to use the 355 and talk serial (probably at logic levels) with the Arduino.

Let me know if that answers your questions.

I appreciate it, and it's very helpful, but I'd still like to know the native signal voltage levels for the BR-355 (without the conversion cable).  Clearly I can use it with the conversion cable, but I would then have to convert back to logic levels on my end.

Thanks again.

[GS_TECH01]

Thanks for providing that link to the Arduino board.

Let's say, if you don't plan to use the RS232 Cable Set and you prefer to have the BR-355 to be connected directly into the board, perhaps you can refer to this forum posting (http://www.usglobalsat.com/forum/index.php?topic=3640.msg9421#msg9421) for the pinout diagram of the BR-355. You should be able to get some idea on how you can make them work together.

Just for your reference, this is the pinout diagram of the BU-353: http://www.usglobalsat.com/forum/index.php?topic=4314.0

[spork]

Thanks!  I'll take a closer look tonight, but that looks like it has all the info I'd need.  It appears the serial cable is a "straight-through", so I suspect the signal voltages are standard RS-232 level.  But that's easy enough to check on a scope.

[GS_TECH01]

Yes, just take a look at the pinout diagram and it should be able to provide the info that you need. Thanks.

[spork]

The pinout diagram is very good, but it doesn't specify the signal voltages.  I'm assuming they're standard RS-232 level signals (as opposed to logic level).  But I'll check them out on a scope.

Thanks again.

[scruzin]

I've just joined the forum and noticed this thread.  I just successfully interfaced my BR-355 to my Arduino Uno.  In fact, I found two ways to do it.

1) Method 1: Invert signal first and feed to Arduino's UART
Invert the BR-355 TX signal and connect the inverted output to the Arduino UART's RX pin, i.e., pin 0.  (I used a 2N7000 MOSFET with an 83 Ohm pullup resister to make a simple invertor).

2) Method 2: Have Arduino do signal inversion in software
Connect the BR-355 TX signal straight to a regular digital pin (I used pin 10) and use the SoftwareSerial library, specifying 'true' for inverted signal.  Your Arduino sketch will have code like the following:

#include <SoftwareSerial.h>

SoftwareSerial gpsSerial(10, 11, true); // RX, TX, inverted signalling

void setup() {
  Serial.begin(4800);       // BAUD rate = 4800
  gpsSerial.begin(4800);  // BAUD rate = 4800
}

void loop() {
  while(gpsSerial.available() > 0) {
    const char ch = gpsSerial.read();
    Serial.write(ch); // just echo what we read
  }
}

In neither case was any other signal conditioning required to use the BR-355 with the Arduino. Just make sure you ground the RS232 shield wire too. 

[GS_TECH01]

Hello scruzin,

Welcome to the forums! And, thanks for sharing your setup procedures with the Arduino Uno board.

This would really help out other forum members and end-users in connecting the BR-355 wiht Arduino. Thanks.