Testing the Dealextreme ET411 GPS module

Ordered the Dealextreme GPS module about a week?? ago, came really fast, made a small test board:

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That little pink thing with the red LED is the module. It says RS232, but really is only 3V logic level in and out, so I added a 7805 for its 5V supply, and a MAX232 (on the back):
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In a free moment of anticipation I scribbled some software parser for the messages it was supposed to send, and INDEED, it works!
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Took some time to get a first fix, probably thought it was still in China, but now it locks in a few seconds, and that is indoors! Very good and sensitive chipset. No need to even send commands to it, by default its sends all possible data every seconds, your PC needs to be able to keep up though. Its position and UTC time seem OK too. Came very fast directly from Nanshan District Shenzhen China, had to sign for it. Seems Dealextreme is indeed just a frontend?

Anyways I am happy with it. The parser I wrote in C, and is just a quick hack, needs some work, if anybody wants it I can put the source code (Linux) on the website. I am sure there are plenty of better programs, but hey this is more fun.

I measure about 30mA (inclusive MAX232), the MAX runs on 5V, and to match the logic level I added a divider 2k2 / 3k3 to make the 5V signal into 3V signal. Reverse the 3V is accepted by the MAX on 5V. RS232 USB adaptor to laptop, there you go.

Reply to
Jan Panteltje
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sensitive chipset.

it.

logic

Nice work Jan, looks like a fun project!

I'm glad you've had good luck with DealExtreme. I ordered several items from them in early January, and it took about 3 months for any of them to be shipped, and then another 2 months for some of the items to dribble in. The Chinese New Year might have been part of the problem. Several items I ordered never shipped at all, and I needed to cancel them.

One of the items I ordered arrived DOA, and at first their customer service people didn't want to honor their return policy and wanted me to get it "repaired" somehow locally. Yeah, sure. They eventually allowed me to send it back to their return address in the US. Maybe I'll get a replacement in a few months, maybe not. I'm not super-upset over it; given the nature of the company I knew going in it was a case of caveat emptor and that I might be disappointed with their service.

I'm pretty sure most of the items available aren't kept in any kind of stock and are either just-in-time ordered from the manufacturers or drop-shipped, so anything you buy is pretty much at the mercy of what the suppliers are up to.

There are a lot of cool parts like the one you used for your project available; it's just unfortunate that, at least for me, the fulfillment aspect was so shoddy.

Reply to
bitrex

sensitive chipset.

it.

logic

Nice!

Ed

Reply to
ehsjr

logic

Very nice work there getting it going.

May I recommend that next time you have to interface to a "TTL serial" device like this that you pickup one of these cables...

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I keep several on hand just because they are so darned useful and time saving.

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Michael Karas
Carousel Design Solutions
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Reply to
Michael Karas

logic

For those trying this at home, don't forget to configure the FTDI cable's EEPROM to invert the TXD and RXD signals. "TTL serial" will mark low, just like RS-232, but the FTDI chip defaults to talking to a UART's output, which will mark high.

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Rich Webb     Norfolk, VA
Reply to
Rich Webb

I have searched high and low on the Dealextreme web site, but could not find the "ET411 GPS module".

Does any one have a direct link ?

Thanks

Reply to
hamilton

On a sunny day (Sat, 12 May 2012 09:23:24 -0600) it happened hamilton wrote in :

The link is on the same page you referred to:

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from
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Reply to
Jan Panteltje

On a sunny day (Fri, 11 May 2012 21:33:47 -0400) it happened ehsjr wrote in :

sensitive chipset.

it.

logic

Thanks!

Reply to
Jan Panteltje

On a sunny day (Fri, 11 May 2012 22:29:34 -0700) it happened Michael Karas wrote in :

logic

That is a nice solution, but at 16Euro59 (about 21$) it is more expensive than my module, and that is ex shipping!

Reply to
Jan Panteltje

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THANKS

Reply to
hamilton
[snip]

Hi Rich,

Just noted, you have the same kind of newspaper (Pilot) we have here... hard-left biased. ...Jim Thompson

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| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
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Reply to
Jim Thompson

On a sunny day (Sat, 12 May 2012 15:02:12 -0700) it happened Don Y wrote in :

Yes I noticed, but then he has CIA and I am sure they know me ;-)

I far as a know from 'looking', the (I left them visible, top of this posting) 'pdop, hdop, and vdop, stands for ... vdop = vertical dilution of position. If that is in meters, then clearly something is wrong. I see altitude slowly changing all the time between -15 m and +10 m relative to sea level. Could be because it is indoors, and lots of waving trees nearby, even a miracle it can see satellites that low above the horizon. So there could be multipath too.

The plan now is to rewrite the soft in PIC18 asm, and use one of the 24LC256 EEPROMs and carry it around a bit and store data, Then later I can analyze if it makes sense.

I guess I could integrate of many seconds for elevation.

I payed US$ 28.30, made 22,01 EUR (paypal).

Reply to
Jan Panteltje

No. They are "quality measure". '1' being "ideal" and larger numbers representing decreasing quality. I suppose there is a mechanism, somewhere, to relate them to actual metrics.

miracle it

OK, I'll buy that...

EEPROMs

Sounds like a plan. I might be tempted to suspect interference (from your PC, etc.) but the other figures seem to discount this as a possibility.

It is reporting this based solely on GPS data? (i.e., one of my handheld GPS's uses a barometric altimeter for that)

I guess not bad for hobbyist type uses.

Reply to
Don Y

On a sunny day (Sun, 13 May 2012 02:40:30 -0700) it happened Don Y wrote in :

OK, thanks for the info, I need to google a bit for that it seems.

Funny I have two pressure sensors on my desk now, both are for car tires though... No, this is GPS only, I am pretty sure the module has no pressure sensor,

It is pretty good, the SiRF star III chipset. When I was much younger I was into airplanes, now about those DIY drones.... I had this idea to make a 'flying board',

4 movable propellers and the right angle of attack... Dunno if it ever comes to something that actually flies. Good for years of fun, these modules :-)

I just added a set clock command, it sets the PC system and hardware clock to GPS time. No more lookup to NIST time servers.

Reply to
Jan Panteltje

though...

I've never looked into how the sensor in that (my) GPS gets calibrated. Seems like it would lose calibration from day to day as the weather changes (??). Maybe it initializes with the GPS and then is used thereafter (I have little care for knowing changes in elevation when using that device. Mainly just trying to get a feel for how far things are, on foot)

Probably too slow on the update rate for you to get much practical use from it.

GPS time.

It should be relatively easy to throw together a stratum

1 time server using that box, a stationary/reliable antenna and a small NIC-enabled MCU. Then, *all* your machines could have stratum 2 quality time! :> Practically all the software to do this is already available open source. (and I know there are PC clients that should work out of the box -- I have one on my machines)
Reply to
Don Y

Probably he would want to combine something like a 6 DOF IMU with the GPS and fuse the data together (eg. with a Kalman filter). The GPS has excellent low frequency performance and the IMU has good high frequency performance.

If he's serious about delivering that package to the right address in AZ, and suspects the GPS may be interrupted, maybe a camera and terrain following.

GPS time.

Best regards, Spehro Pefhany

--
"it's the network..."                          "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
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Reply to
Spehro Pefhany

I think that's how the ICBM's work. Some sort of absolute position sensing system to make general corrections to course/position while the gyro handles instantaneous corrections. (?)

Ha! If he's got *that* much expertice and "free time", I suspect he can find better targets! :>

I still think the stratum 1 time server a more practical idea! (though I wonder how temporally predictable the I/O from the module is likely to be -- I cringe each time I think "deal extreme"...)

Reply to
Don Y

On a sunny day (Sun, 13 May 2012 15:41:16 -0700) it happened Don Y wrote in :

Pressure at 'zero' altitude is very different for different locations and different times. I did look up local pressure from the local weather station on the internet, I am close to it, and calibrated my barometer with it... That is a mechanical one. These little tire pressure sensors are just a chip on a PCB, with a blob of flexible transparent stuff on it. The air pressed against the blob that presses the chip, some LSI and a LCD display, 3V battery.

Update is 1x per second , I think this is fast enough for position. True altitude would have to be some echo, light or laser perhaps.

GPS time.

Right. I improved the software some, fixed some silly bugs, improved the 'presentation' of the data, now maybe I should get one of those little single board Linux computahs, one with enough I/O pins to actually do something AND mounting holes, that rules out any strawberries I think. That way I can do everything in C with gcc and do not have to rewrite stuff.

At a later time I will update the software at the website.

PS: I found the meaning of hdop, vdop, etc:

From wikipedia:

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DOP Value Rating Description

1 Ideal This is the highest possible confidence level to be used for applications demanding the highest possible precision at all times. 1-2 Excellent At this confidence level, positional measurements are considered accurate enough to meet all but the most sensitive applications. 2-5 Good Represents a level that marks the minimum appropriate for making business decisions. Positional measurements could be used to make reliable in-route navigation suggestions to the user. 5-10 Moderate Positional measurements could be used for calculations, but the fix quality could still be improved. A more open view of the sky is recommended. 10-20 Fair Represents a low confidence level. Positional measurements should be discarded or used only to indicate a very rough estimate of the current location. 20 Poor At this level, measurements are inaccurate by as much as 300 meters with a 6 meter accurate device (50 DOP × 6 meters) and should be discarded. The DOP factors are functions of the diagonal elements of the covariance matrix of the parameters, expressed either in a global or a local geodetic frame.

This is also interesting about 'knots' for speed:

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And a know seems to be 1.852 km/h.

So it seems there is a problem with vdop, as it shows now 2.6 for 5 sats used and a very unlikely altitude (10 meters below sea level). :-)

Reply to
Jan Panteltje

You need three accelerometers and three gyros for a 6 DOF IMU.

ICBMs used to use (and quite possibly still do use) a star tracker to do the absolute guidance for a portion of the flight, so no GPS required (I think you have to assume that GPS satellites may not be available in a situation where ICBMs are fired in anger). It's safer that way too, because otherwise it would increase the advantage of a first strike by either side.

IMUs are cheap enough now that they can be used in light aircraft and UAVs. A tactical grade one is less than $30K and I have a small (relatively noisy and drifty) one that cost less than $1K. You can probably buy a MEMs one for less than $300 nowadays, suitable for a small UAV. It would be interesting to put a higher end one together with some of the FOGs and high end accelerometers available these days.

Can you implement IEE-1588 PTP? If there is jitter, but high absolute accuracy, it can be averaged out, down to the sub-microsecond level.

Best regards, Spehro Pefhany

--
"it's the network..."                          "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
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Reply to
Spehro Pefhany

On a sunny day (Mon, 14 May 2012 07:49:27 -0400) it happened Spehro Pefhany wrote in :

This module only sends data once very second at 4800 Bd. But MAYBE, as it has a LED that flashes in sync with the NMEA time data send, you could PLL an oscillator to the 1 second LED, and that way interpolate to some ms.

ICBM I dunno, have you seen the movie 'Astronaut farmer? But I have this idea that a stealth looking drone could have pretty good aerodynamics and would be easy to make (except engine). Very flat bottom, and some angled flat surfaces gives you wing profile in a cheap way, wonder why they are so expensive. . . . . . ----------------------------- front

Reply to
Jan Panteltje

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