Moderator

Jumper(s) for APM2 onboard GPS?

UPDATE: See the manual.

Hey guys, this is mainly a question for our friends at 3DR, but anyone who has looked at the traces on the APM2 daughterboard, and knows the GPS module, could offer ideas.

I wonder what you'd think about (as a hack, as a revision to the APM2 daughterboard, etc) installing some jumpers or switches to "disconnect" the onboard GPS, as needed. We might also add a battery socket to maintain the almanac, for those who want to accept the extra weight of the small battery, but that is another topic.

I have a small but growing fleet of APMs, some APM1 and some APM2s. However, I never have enough, so I find myself swapping them around as needed. I leave the magnetometers, air speed sensors in place and connect them as needed. Some airframes are better served with an external GPS, but I would prefer to have all my APM2s be, physically, the same. That is, I'm willing to buy all my APM2 with the extra cost of the onboard GPS whether or not I need it, in order to ease my "fleet management" if you will. If the daughterboard were not soldered in place, I might instead get extras, but this approach might work best.

However, I would also like to buy or use uBox and other external GPS units, as needed. I think this represents opportunities for the 3DR and affiliate stores. Many users will purchase the APM2 w/GPS, and some will later decide they want to use an external. Some will buy a separate unit w/o the GPS, but most will not. Most of the population simply live with the existing GPS. However, if there were a switch or jumper(s) to kill the onboard GPS, then casually swapping to an external GPS (and, casually purchasing additional GPS units) is easier. It also allows for subsequent upgrades (opportunities for sales) to future GPS units. 

As a hack, are there recommendations on which trace(s) are best to cut and/or install a jumper for an existing APM2? I imagine there are a couple of ways to do this, not all are ideal. Is there any merit to a revision of the APM2 where there is a jumper or switch for the GPS? 

Thoughts? 

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  • Moderator

    The manual has been updated with a recommendation by Jani, easier and simpler than (and similar to) some of the ideas we've been playing with here. 

  • I installed a battery and now I get s gps lock almost immediately on power up (8 to 13 sats in view in a minute).  I also have no JP1 installed and only power the apm2 from the input rail using a ubec that outputs 5.03 volts.  Anything much higher than 5.0 volts leads to gps problems I noticed (it is also in the wiki).3692459474?profile=original

  • Just a thought. But I warn you I do not have my APM2 yet so I have nothing to look at to see if its feasible.

    What would be the issue with coming up with a another small PCB that had what ever was required to disable the GPS and fix the the 3d Fix led that could be soldered in place of the GPS module and had the GPS module mounted to the top of it.

    It would be sandwiched between the GPS module and the APM2 daughter board. 

  • Hey guys, I liked the idea of the jumper, but decided it was going to be messy and I wasn't going to need the onboard GPS for a while (or I was lazy?). Instead I just soldered a 10k 0402 SMD resistor between pins #2 and #3 on the GPS module. The 3D fix light on the daughter board is always illuminated, but this is meaningless. The external GPS works flawlessly. Here's a picture:

    3692447964?profile=original

    I figure when I want it back this is going to be really easy to remove

    Colin

  • Thanks for doing these tests Mike. I have an idea for the mechanical solution, but I doubt the APM will be so pretty after ;-)

    My idea is to take one of the pins out of a two pin male header. The hole in header (from the removed pin) would slide over the GND daughter board mounting pin next to the 3D fix writing- the other pin can float outside the daughter board. This leaves two pins next to each other ready for the jumper. Now solder pin 2 of the GPS to the new header (the one floating). All of this would then be secured tightly in place with hot glue or Shoe Goo (really good stuff).

    Then the GPS can be disabled by sliding the jumper into place.

    My advice for soldering the pin #2 is to heat it up and add a small amount of additional solder. Then with a small ball of solder on the end of the iron (to conduct heat better), push the resistor into pin #2 while heating the leg of the resistor. This means you don't have to touch the pad while adding the resistor. I'll make a video when I do it later this week if it helps.

    If you cut the power line, I believe you will still have the 3D fix light illuminated no matter what. It takes the GPS to be powered up and pulling the transistor high for it to go out. I think it being illuminated could be a good indication that the jumper is correctly seated when you power up- when was the last time you instantly got a 3D fix ;-)

    Also, the datasheet says in the disabled state the current draw is about 15uA, so nothing.

    The resistor value, I don't know. On pull-up resistors and the like with Arduino, 10k is pretty common. So I would guess something similar here. The 4K seems to have worked well for you, I'd be inclined to just stick with that. You need to make sure that pin #2 is below 0.25v by a reasonable margin.

    I think cutting will also work fine, so do that if you're more comfortable. I just don't like cutting tracks :-)

  • No doubt as Chris says, in a later hardware release, all will be good. As for those of us now with the current hardware we own, posed with the need (for whatever reason) to implement external GPS, where do we turn? Below refers to another of your posts on the same subject 

    If I don't get an answer there, I will eventually start cutting traces on one of my boards to figure it out myself, and I will post something there. Either way, we'll have an answer there eventually.

    Let me know when you go for the chop Mike, I'll go in sympathy with you. I have just been through 15 odd pages of the hardware forum and found 10 threads started on the same topic, for nil posted results. One member has apparently done it successfully but could only manage to post a thumbnail size picture of his attempt. I have familiarized myself with the Tx pin on the gps unit and feel confident enough to give it a snip.

    In my case I will just need to make sure I have earth continuity between the other gps unit I have installed in the aircraft (for antenna tracking) and then piggyback the Tx from that unit onto the daughter board of APM2. Should that not work, I have a U-blox to try on the external gps header.

    5 minute job............ ... :)

    Any comments on the chance of success with this mod Chris? I figure if it all goes pear-shaped I'll have an excuse to buy the external gps version of APM2 right? :) 

  • 3D Robotics

    The next rev of APM 2 will have that. 

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