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Topic: Bathymetry Measuring Apparatus (Read 2 times) previous topic - next topic

SlupreMand

Hi

It's a cool project you have here, i'm looking forward to hear how it goes.
I'm a noob myself, still tinkering with blinking LED's and motors.

I just have a thought regarding the issue logging the data simultaneously.
The question might more be to the guys following the thread with some more experience.

Would it be possible to take a time stamp from the GPS NMEA sentence and stamp the transducer data with it? then you would have a latency from the equipment.
Many GPS systems can output more than one sentence at once (GGA, GGL, ZDA(time and data as i recall), ect.)
I'm sure it will involve some advanced programming if its possible.

Just putting it out there :)

GeoGuy

This guy has done something very similar to my project:

http://letsmakerobots.com/node/21098

He gives his sketches but they are way different than what I have been putting together. I asked him about the logging data simultaneously problem and he kinda shrugged it off like it wasn't really as big of a deal as I made it out to be.

SlupreMand

You can argue that it really depends on what the collected data is used for, if its just for fun or you actually have to use the data for serious purposes.
I have been working with Multibeam echosounders for a couple of years, here the latency of all instruments is of high importance, but here you also have gyro and motion sensor, so if one sensor is off by a second the result bad.

What rate does the transducer send data with compared to the GPS?

It might be worth to think about the accuracy of your GPS, compared to your speed, and the transducer "latency" during logging.
If the GPS has an accuracy of a few meters or more, how much do you gain in data quality from a correct logging time?
I must note, i dont know what systems you are using, so you might have far better accuracy if you are using an argumentation system.
see http://www.gps.gov/systems/gps/performance/accuracy/


jenkin507

Hi all,

strange coincidence - I am working on exactly the same problem.

I am using a GPS module that transmits NMEA 0183 and is mounted on a data logger shield

http://www.ladyada.net/make/gpsshield/

I can get this to work no problem with the code "supplied" with the unit - https://github.com/adafruit/SD-Basic-GPS-logger/blob/master/SD_GPSLogger.pde. I am using an UNO so am using softwareserial for communication.

I also have a depth sounder that transmits NMEA 0183 data - a Garmin Intelliducer. I can connect it to the arduino and with a very slight modification of the gps program (get it to look for the appropriate NMEA string for depth instead of gps) I can log the data from the depth sounder. I did have to run the output of the depth transducer through an inverter but that was no big deal.

So, I then thought to define two softwareserial ports, one for gps and one for depth and alternately poll them. I have tried many iterations and versions of this but basically cannot get two softwareserial ports to alternate reliably.

Any clever folks out there with a solution? Will share all code once we get it working nicely

Thanks,

Peter

wildbill

From the documentation for SoftwareSerial.listen:
Quote
Only one software serial port can listen at a time; data that arrives for other ports will be discarded. Any data already received is discarded during the call to listen() (unless the given instance is already listening).


Could this be your problem? If not, it's time to post your code.

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