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How fast can I log data? — Parallax Forums

How fast can I log data?

Brian SmithBrian Smith Posts: 44
edited 2005-12-20 14:17 in BASIC Stamp
Im using my basic stamp 2·and Stamp DAQ to log gps data in excell. Im currently using a garmin etrex that outputs garmin text format at 1Hz. I want to get a Garmin 18 5-hz.

Heres the gps 18 manual. I want to use the 5hz version. ·http://www.garmin.com/manuals/425_TechnicalSpecification.pdf

How can I know if my BS2 will be fast enough to recieve the data at 5hz?·Would I·benefit from·using a faster Stamp model?
Im also logging a few other sensors. Acceleration from the Memsic accelerometer and three temp sensors.


P.S. I plan to switch to an onboard memory and eliminate the Stamp DAQ and Laptop.

Comments

  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2005-12-20 00:37
    Brian,

    ·· This really depends on how much data we are talking...at 5hz though, you'll probably need a BS2px and fixed-length string output from the GPS to use the ScratchPad RAM store function.· Also, consider this, at 5 hz you will fill most memory chips very quickly with the data from a GPS.· If we knew exactly what information (fields) from the GPS string you're saving that would help to figure out just how much.

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    Chris Savage
    Parallax Tech Support
    csavage@parallax.com
  • Brian SmithBrian Smith Posts: 44
    edited 2005-12-20 00:47
    I just want Latitude and Longitude.· I want up to the fifth decimal eg: 36.10594· 85.30125. Im gonna post process the data to get velocity, acceleration and so on.attachment.php?attachmentid=74102
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  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2005-12-20 01:09
    Brian,

    ·· It still sounds like you're going to need at least 14 bytes per sample, times 5, etc. and you're looking at 256KB of memory per hour of logging.

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    Chris Savage
    Parallax Tech Support
    csavage@parallax.com
  • Brian SmithBrian Smith Posts: 44
    edited 2005-12-20 03:31
    Well Im logging to a pc now so storage inst an issue yet. But will my BS2 be fast enough to do what I want?
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2005-12-20 04:45
    Depending on the baud rate, I believe a BS2px may be fast enough.· But without knowing more information it would be hard to be sure.· There are too many variables.

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    Chris Savage
    Parallax Tech Support
    csavage@parallax.com
  • achilles03achilles03 Posts: 247
    edited 2005-12-20 14:17
    I think baud rate will definately be your biggest issue. With the BS2, I've been able to log 250+ bytes per second using an external eeprom. But what it comes down to is this: can your BS2 record/export the needed data between the time it stops listening to the GPS unit to the time the next GPS import occurs? This really depends on how fast you are importing it (baud rate) and how you're recording/exporting it. You want the BS2 operating at the fastest baud rate possible you can get without errors.

    Remember, you don't have to "listen" to the entire GPS sentence if you're only concerned with, say, the 10th-18th characters. Also, you don't have to start listening at the begining of the GPS sentence (ex: if you're always going to be in the Northern Hemisphere, you might use "N" somewhere in the sentence to indicate the SERIN start, if you're only concerned with data that comes after "N", and you can't export the data fast enough before the next GPS sentence occurs).

    Dave
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