GPS Logger Shield vs. Ultimate GPS + micro SD breakouts

[astronomerdave]

I want to log GPS data plus one other sensor, both at 5-10Hz (the other sensor should be read and logged at the same time as each GPS datum). I'll display these data as well as log them to memory for later retrieval/analysis on a computer.

What are the differences between using the GPS Logger Shield + EM406A vs. using the combination of the Ultimate GPS Breakout plus the MicroSD Breakout (other than the fact that the latter combination is cheaper than the former, $55 vs. $80)?

The GPS units are different, although both claim a 10Hz data rate (except I thought I saw a post which implied the ultimate shouldn't be read that fast -- can't find that post at the moment).

Do they both use the same software?

Is there any advantage to one system over the other?

Thanks,
--David

[adafruit_support_bill]

The advantage of the shield is that it is a shield & plugs directly into an Arduino to make a compact unit. Of course, you could simply mount the breakouts to a ProtoShield for the same effect. I am not aware of the limitations on read-speed on the Ultimate that you mention. If you manage to locate that post please link it here. Both units will work with the same logging software. Although there are additional features on the Ultimate which can be configured with ultimate-specific commands.

[astronomerdave]

OK, great. I happen to have an older GPS unit in another project so I tried it on the Arduino tonight; this unit just spits out serial data and I've connected it up like you describe in your breadboard friendly GPS unit. However, I would rather use the hardware serial rather than the software serial; is this possible?

In other words, I want to use the SD logger (over SPI) with a bare GPS (over hardware serial). I've tried the software serial, reading the GPS and then printing it back to the hardware serial to see on the serial monitor, and I see the GPS messages.

I've also connected the GPS to the hardware serial and uploaded a blank sketch and started the serial monitor, then I see the GPS messages being spit out fine. But how do I read the GPS messages from the hardware serial, in order to write them to the SD? It seems like if I open the hardware serial with

Code: Select all

Serial.begin(57600);

then I can't do anything other than talk to the host computer, and if I don't open the hardware serial then I can't get data from the GPS. There must be a way to do this but I haven't learned it yet.

Thanks

[adafruit_support_bill]

Hardware serial is connected directly to the USB/Serial converter on the Arduino. If you connect the GPS to pins 0 & 1, it will be wired in parallel to the host computer connection. This should work as long as the baud-rates are the same and you don't try to send anything from the host computer. You will need to disconnect the GPS to do any uploads.

[astronomerdave]

Then this should work...

Code: Select all

void setup() {
  Serial.begin(57600);     // gps TX,RX on 0,1
}

void loop() {
  if (Serial.available()) {
    Serial.print(Serial.read());
  }
}


except that it doesn't. If I hold in the reset button -- so that presumably the microcontroller isn't doing anything -- then I see the NMEA messages come out. As soon as I release the reset button then nothing is printed anymore, except sometimes I see one more sentence.

However, the following code does work,

Code: Select all

#include <SoftwareSerial.h>
SoftwareSerial gps(3, 2);   // gps TX,RX on 2,3

void setup() {
  Serial.begin(57600);      // serial monitor
  gps.begin(57600);         // serial to GPS
  }

void loop() {
  gps.listen();             // doesn't seem to matter if this is here or not
  if (gps.available()) Serial.print((char)gps.read());
  if (Serial.available()) gps.print((char)Serial.read());
  }


[astronomerdave]

Then this should work...
except that it doesn't.

You know, I once had a college professor who repeated this mantra,

"it's in the wiring"

without even looking at your problem specifically, and he was always right.

[adafruit_support_bill]

So it's working for you now?

[astronomerdave]

Yes, it is, thank you!

In the simplest form, I have the GPS's pin 3 TX line connected to the Arduino's pin 0 RX (don't need to send commands to the GPS) and the following code DOES work:

Code: Select all

void setup() {
  Serial.begin(57600); 
}

void loop() {
  if (Serial.available()) {
    Serial.print(Serial.read());
  }
}


And yes, I do have to disconnect the GPS when uploading to the Arduino. Thanks again.