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What is the cheapest way to get a GPS + solid state gyro?

Discussion in 'Embedded' started by Peter, Apr 29, 2012.

  1. Peter

    Peter Guest

    I am looking at a project which requires a simple GPS receiver (not
    waas/egnos) and a low grade solid state gyro (not a "level") like the
    ones you get in smartphones.

    The build volumes will be initially a batch of 100 and later perhaps
    thousands, but not more than that.

    What would be the currently recommended GPS module or chip, and a
    solid state gyro component?

    There is a lot of stuff on the market...

    One requirement is reasonably low power - milliamps rather than 10s of
    milliamps. I have no idea if that is possible.

    Ideally the two items can be obtained for under $20-30.

    Any pointers would be much appreciated.
     
    Peter, Apr 29, 2012
    #1
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  2. Peter

    Tim Wescott Guest

    I'd start by checking DigiKey and Mouser for the gyro chips, and maybe
    Circuit Cellar ads for GPS modules (as well as DigiKey).

    There's not a lot of GPS augmentation that you can do with a gyro and no
    accelerometer -- what are you trying to do?
     
    Tim Wescott, Apr 29, 2012
    #2
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  3. Most of the chips are already three axis, so don't get high hopes of
    finding cheap solutions for two axis, when the rest of the world made
    three axis parts cheap for you already.
     
    Chieftain of the Carpet Crawlers, Apr 29, 2012
    #3
  4. I have not yet found a GPS solution that can give 1HZ updates and draw
    less than about 20mA. There are some that can go into a low-power sleep
    mode and wake up on command to give a fix. However, when awake, they
    still draw 20 to 30mA. To get the overall power down, you need a fairly
    low duty cycle.
    The low end for GPS chips that I've used is about $30 qty 1.
    Mark Borgerson
     
    Mark Borgerson, Apr 30, 2012
    #4
  5. GPS module + chip antenna should be around $17 quantity one.

    Cost of gyros and translational accelerometers depends a lot on their
    performance, from a few dollars up to serious dollars/euros for
    military grade stuff.

    Best regards,
    Spehro Pefhany
     
    Spehro Pefhany, Apr 30, 2012
    #5
  6. Which module would that be? A few years ago I used a now-discontinued
    Delorme module that was about $35 qty 1. I couldn't find anything in
    stock at DigiKey in the $17 price range.
    Mark Borgerson
     
    Mark Borgerson, Apr 30, 2012
    #6
  7. Spehro Pefhany, Apr 30, 2012
    #7
  8. Peter

    miso Guest

    The GPSs in cars (built in units) have accelerometers. It makes the user
    experience better since it can sense a turn before differential
    waypoints can sense it. I don't think they have to be very good to do
    that task.

    They can also do dead reckoning fairly well, but I've never been out of
    GPS contact for more than a few miles.

    There is a usenet group on gps.
     
    miso, Apr 30, 2012
    #8
  9. I noticed when driving a new car in Europe that the nav system managed
    to track fairly well through long tunnels. Makes sense that they would
    stick an accelerometer and/or gyros in there for when the GNSS
    satellite signal is not available- tunnels and urban driving between
    tall buildings. Even a lousy MEMS gyro won't drift that many degrees
    in a few minutes.

    Best regards,
    Spehro Pefhany
     
    Spehro Pefhany, Apr 30, 2012
    #9
  10. Peter

    Tim Wescott Guest

    I'm nearly 100% sure that if you want to do credible dead reckoning you
    need accelerometers and gyros, not just one or the other. Gyros don't
    mean much when you don't know the acceleration, and accelerometers don't
    mean much when you don't know the vehicle direction.

    If there's no skidding going on, a good odometer and a steering position
    sensor may work better than an IMU, though.
     
    Tim Wescott, Apr 30, 2012
    #10
  11. Jan Panteltje, Apr 30, 2012
    #11
  12. Peter

    linnix Guest

    Why can't you figure out the direction with 2D accelerometers?
     
    linnix, Apr 30, 2012
    #12
  13. Peter

    hamilton Guest

    hamilton, Apr 30, 2012
    #13
  14. Peter

    Rich Webb Guest

    All six degrees of freedom, three rotation and three translation, are
    required for a general-purpose INS. *But* if you're able to constrain
    the problem to, say, non-skidding/slipping car behavior then yes, two
    properly mounted orthogonal accelerometers could do a pretty reasonable
    job, modulo the usual caveats of noise and sensor drift, given an
    initial (or periodic) knowledge of heading and position. Better if you
    also include the vehicle speed in the mix, of course.
     
    Rich Webb, Apr 30, 2012
    #14
  15. Check the manufacturer website, I doubt DX will give yo anything more
    than a padded envelope marked "gift".
     
    Spehro Pefhany, Apr 30, 2012
    #15
  16. Peter

    Tim Wescott Guest

    Because without a gyro or some other angular reference you don't know
    what direction they're pointed.

    I suppose that if you were really cost-conscious you could assume no
    skidding and take sideways acceleration to be an indication of turning
    rate -- but that's a pretty tenuous connection to reality.

    --
    My liberal friends think I'm a conservative kook.
    My conservative friends think I'm a liberal kook.
    Why am I not happy that they have found common ground?

    Tim Wescott, Communications, Control, Circuits & Software
    http://www.wescottdesign.com
     
    Tim Wescott, Apr 30, 2012
    #16
  17. How about a compass module for orientation? That'll probably work OK for 2D
    navigation tasks between GPS fixes. Not sure what the OP needs.
     
    Paul Hovnanian P.E., May 1, 2012
    #17
  18. Peter

    krw Guest

    That's all the automotive GPS units I've seen have.
     
    krw, May 1, 2012
    #18
  19. OK
    The FM modules for Hongong I have, at least had a pin connection diagram...
     
    Jan Panteltje, May 1, 2012
    #19
  20. Thanks!
    I have downloaded the pdfs, maybe I buy one just for fun,
    could be an other PIC project, and combine with my fluxgate compass...
    Years of fun ahaead...
    Maybe needs a more powerful computah, one of those recent Linux based boards
    perhapds (display maps on LCD etc).
    ;-)
    I would not use FAT filesystem ....
     
    Jan Panteltje, May 1, 2012
    #20
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