[Gta04-owner] GTA04A4 starts shipping tomorrow
lionel.broche at gmail.com
Tue Jan 31 00:47:45 CET 2012
Good job, keep up with the good work!
How does the GPS performs now, with the HW fix and internal antenae?
On 31 January 2012 05:13, Dr. H. Nikolaus Schaller <hns at goldelico.com>wrote:
> Dear all,
> you may have wondered a lot why it was so quiet about the GTA04A4
> boards in the last weeks. And nobody did report about unboxing
> experiences, because nobody did receive a new GTA04.
> The reasons where manifold. It started with soldering issues where they
> had to make a new stencil. This improved soldering quality a little but it
> was still not perfect. So we got much less good boards out of the soldering
> machine than planned and chips had to be replaced...
> Then, we did test the boards completely. It turned out that they still had
> some minor issues. The most maddening bug was that there was an error
> in the GND flooding of the backup battery. Therefore it was shorted on the
> PCB and could not work.
> After fixing this and testing more, we found out that the new circuit that
> is intended to allow the CPU to control the power of the UMTS modem
> through a GPIO did not work as intended. Rather than shutting completely
> down it did put the module into reset state. This would have been ok, if
> reset would be the same as power down. But the module draws 16 mA
> in this state. Even more than a not powered down modem in the GTA04A3
> boards which draws 3-10 mA and can wake up the CPU...
> So we finally found a way to solder a NPN transistor with built-in bias
> resistor to the position of some test pads and other resistors to make
> it work. This made us again bring the boards to the factory and
> have them do some hand-rework. And wait some days...
> Then, last week, we got the first boards that did pass all automatic
> tests and could power down completely (to some 300 uA for RTC).
> Happily we did install them into the first GTA02 cases to build the
> "OpenPhoenux" (GTA04 Complete) units. They worked fine, until we
> wanted to operate the GPS. It did not work well with internal antenna,
> but really excellently with an external antenna (up to 11 of 12 satellites
> used for navigation).
> We found out that the U.FL antenna socket was mounted in the
> wrong orientation (180 degrees rotated). This shorts the power
> supply of the internal Antenna (which has an amplifier built in).
> So, boards did go to rework again. Now, GPS with internal antenna
> was a little better, but still very weak.
> After 3 days of intensive research (incl. this weekend) we did find the
> cause: it is the same as it was for the GTA02A5 board . The SD card
> clock. It is 25 MHz and 25 * 63 = 1575 MHz, i.e. the GPS frequency.
> This means that the GTA04 creates some noise which is neglectable
> in more than 5cm distance with an external antenna, but not for the
> active GPS antenna built into the case. And some boards and
> antennas are a little better and others are a little worse so that it
> results in a basically working, but very unreilable receiver.
> The main problem was to find a measurement setup that gave
> reproducible results so that we could not only compare devices, swap
> antennas and try different shielding scenarios, but also check the
> effectiveness of measures against the problem.
> Like with the GTA02 there is a hardware and a software fix. The SW fix
> was to re-enable a feature in the 2.6.32 kernel that we had disabled due
> to problems with the SDIO driver. It appears that it is not at all
> to change anything in the 3.2 kernel. So please forget immediately that
> there is a SW fix :) Because it fixes our unawareness and not a problem...
> The real hardware fix is adding a small capacitor like for the GTA02A5.
> You may wonder why we did not find it earlier. One aspect is testing time.
> The more testing you do the more issues you find. But we simply did
> not have enough GTA04A3 boards to do these tests...
> This time it was better and we could set up, test and compare e.g.
> 5 GTA04A4 boards in parallel. And swap antennas between units etc.
> This simply was not possible before.
> So after having applied this last hand-rework, we have the first boards
> and devices that are in our opinion good enough to really be shipped
> and make you happy! More boards will become available next week.
> And we have some boards to show during FOSDEM next weekend.
> So please come and have a look!
> Finally, it is still time to subscribe to the Group Tour (which will get
> another board redesign where all these things are done right from
> the beginning - but otherwise they are equivalent).
> : http://wiki.openmoko.org/wiki/GPS_Problems
> Gta04-owner mailing list
> Gta04-owner at goldelico.com
Dr Lionel Broche
Aberdeen Biomedical Imaging Centre
University of Aberdeen
tel : +44 1224 553 206
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