APM2 GPS non-functional
Hello, I have been reading over several of the problems people have experienced with the MediaTek MT3329 (?) GPS that ships with APM2. I have not been able to get any signal out of the unit. I have done the check for poor solder joints suggested in one thread. I had an external GPS board from my APM1 so I tried it out on the APM2's I2C and it came on line after about 9 or 10 minutes. Also, I have another MediaTek MT3329 unit from another APM2 that I tried to no avail.
Using the input ground pins as ground, I checked for voltage on each of the 6x2 pins and got something like 4.8V on a few pins, about half that on one pin, and a very slight amount (<1V) on several others. So I don't think it is overvoltage as suggested in another thread. Any suggestions on further troubleshooting? The myriad of posts doesn't instill confidence in these units.
Replies to This Discussion
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Permalink Reply by Tom Gibson on -
Update...
GPS did come on one time while connected over USB. Took about 8 minutes and was about 1/8 mile off.
Rechecked voltage at pins again, this time with GPS board in place, running but not reporting. Readings as follows:
.003 5.4 .007 3.3 3.3 5.35
<-- FWD
2.75 5.4 3.2 .003 0 5.4
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Permalink Reply by Jake Stew on -
Do you have a clear view of the sky? (~180 deg.)
If you do your problem is probably dirty USB power.
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Permalink Reply by Tom Gibson on
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Most of my testing has admittedly been indoors but I have gotten connection there before. I intend to move everything outdoors today to be fair. Regarding the USB power, I have tried both USB and ship's power (with 3DR 900MHz) with same results. Not familiar with "dirty USB power". Also, is 8-10 minutes normal for connection?
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3D RoboticsPermalink Reply by Chris Anderson on -
I can never get a connection indoors. Please let us know how it goes with the outdoors testing.
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Permalink Reply by Tom Gibson on
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Okay, I'm a believer now. Outdoors got a good lock inside of one minute, over USB or 3DR. Guess I was being fooled by chance connections before.
On a related topic (I may pose this on a separate thread if it seems appropriate) -- I will likely need to remote the GPS. Is there an option for remoting the daughter board so I can still use the magnetometer? I suppose I could just make up my own 6x2 cable.
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Permalink Reply by Jake Stew on
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GPS generally doesn't work indoors. When near a window or if your roof is not metal sometimes you can get a crappy lock.
USB power is the other issue. It is very dirty. Ripples, interference at all sorts of frequencies, etc.. This often interferes with the GPS. Laptops and computers with motherboard integrated audio are the worst.
Ever tried to watch analog over-the-air TV while someone turns on a vacuum/blender? That's what USB power is doing to your GPS radio.
The GPS takes 12 minutes to download the almanac data the first time out of the box. Normal cold start takes 35 sec. These figures are for a perfect 180 deg. view of the sky, i.e. bare module out in a field. Dirty power or not clear view will take much longer. In normal conditions it takes a minute or two.
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Permalink Reply by Tom Gibson on
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Update...On second attempt this afternoon, in the same place where I got a quick connection this morning, tried several times for 10 minutes at a time with no GPS lock, neither APM2 nor APM1 GPS cards. AT one point checked terminal screen with TEST>GPS command and was getting G!G!G!G!G's. Finally did get a lock when APM was powered up over USB only. Unfortunately my laptop battery quit before I was able to test over 3DR after getting the lock.
I am beginning to suspect though that the ship's battery and/or ESC has something to do with this, since I was able to get lock twice now on USB only. Any thoughts?
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3D RoboticsPermalink Reply by Chris Anderson on -
Tom, what are you using for non-USB power? (BTW, you can't use wireless telem and USB at the same time; they share the same UART port)
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Permalink Reply by Tom Gibson on
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Yes, understand about the shared port. Using 2 NiMH battery packs supplied with Traxxas Spartan boat package. Btw, have experienced some anomalies with the Traxxas (Castle) ESC, such as ESC switching to LiPo (failsafe) mode when APM is installed. Thinking about doing some tests with bench power supply to eliminate battery charge uncertainties.
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Permalink Reply by Tom Gibson on
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Update 3
Did some tests and found that my Traxxas (Castle) ESC is causing some interference which prevents GPS from working. Also confirmed noise with scope reading. Removed J1 jumper and powered APM with separate 5V source and GPS came on quickly and reliably, both daughter board and external mount (individually). Looking at this for a power supply: http://microcontrollershop.com/product_info.php?cPath=301_429&p.... Seems a bit pricey but will hopefully do the job. Other suggestions welcome.
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3D RoboticsPermalink Reply by Chris Anderson on -
Nice detective work!
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Permalink Reply by Jake Stew on
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Most BEC/UBECs work just fine. I'd start with the cheapest one and work your way up if there's problems.
At $105 for a simple power supply they're just flat out trying to rape you. Looks to me like microcontrollershop.com is a total ripoff site.
Maybe try this... ($5.33)
http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=...
"The shielded PCB design and output EMF coil provide a stable, low noise voltage output."
I'm sure there are other low noise units there also, that's just the first one that came up. I always check hobbyking.com first because they just have the lowest prices I've ever seen for everything.
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