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

[Peter]

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.

 

[Chieftain of the Carpet Crawlers]

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.

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.

 

[Mark Borgerson]

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.

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.

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

The low end for GPS chips that I've used is about $30 qty 1.

Any pointers would be much appreciated.

Mark Borgerson

 

[Spehro Pefhany]

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.

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.

Mark Borgerson

Best regards,
Spehro Pefhany

 

[Mark Borgerson]

GPS module + chip antenna should be around $17 quantity one.

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.

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.

Mark Borgerson

 

[Spehro Pefhany]

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.

GlobalSat or U-blox modules with SiRF III etc. are around $15 shipped.

Eg.
http://www.dealextreme.com/p/eb-365-gps-engine-board-module-with-sirf-star-iii-chipset-80045?item=4

Mark Borgerson

Best regards,
Spehro Pefhany

 

[miso]

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

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.

 

[Spehro Pefhany]

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.

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.

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.

Best regards,
Spehro Pefhany

 

[hamilton]

Do those modules come with any sort of datasheet?

Google found this:

http://diydrones.com/profiles/blogs/cheap-gps-modules-at

 

[Rich Webb]

Why can't you figure out the direction with 2D accelerometers?

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.

 

[Spehro Pefhany]

Do those modules come with any sort of datasheet?

Check the manufacturer website, I doubt DX will give yo anything more
than a padded envelope marked "gift".

 

[Rich Webb]

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.

Yes, it's definitely one of those "works in theory but..." applications.
But in theory, it would work. ;-) In practice, it could be good enough
to work thorough the "urban canyon" effect for brief GPS outages,
although the addition of a simple fluxgate compass would help
tremendously.

 

[Jukka Marin]

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.

Those systems also use the speed/distance information from the wheel
sensors, so the can be pretty accurate. A bit like a hi-tech device
called odometer ;-)

-jm