Hello Everyone, we all know our GPS board (the one that comes with the APM1) has no battery to backup data.
This has the disadvantage to make the GPS not very precise in the first minutes after power up and that every startup is a cold startup (at least one minute to get a 3D fix).
This is because the GPS needs find the satellites without a previous almanac (that is information on position of the satellites visible in that location at a specific time).
As you understand almanac is VERY important. Also considrer that the almanac is sent by every satellite and requires 12.5 minutes to transmit (or so).
From Wikipedia:
"Finally, the almanac allows a single-frequency receiver to correct for ionospheric error by using a global ionospheric model. The corrections are not as accurate as augmentation systems like WAAS or dual-frequency receivers. However, it is often better than no correction, since ionospheric error is the largest error source for a single-frequency GPS receiver. Each satellite transmits not only its own ephemeris, but transmits an almanac for all satellites"
Of course this is not sufficient to have a perfect position: sky visibility, surrounding objects and number of satellites are the key factors.
This is why after a FIX (fixed blue led) number of satellites is very low (5 to 8) and this get higher (10 or 12) after some time of flying.
So, because of this, I decided to bring up an old hack made by Dcaspi, an old friend who worked also on the former Ardurpirates code.
The hack requires some soldering skills, so I suggest you to do it only if you are confident with it.
Beware if you fry the board or GPS unit, I cannot (nor Dcaspi) be responsible for it...
This mod works and has been used for a while.
This is the original location:
Have fun!
Emile
Introduction
If you use the DIYDrones MediaTek? GPS, you're probably aware of the fact that, on each activation, it make take a very long time to get proper satellite lock. The reason is that it always starts from scratch; it is not aware of it approximate geographic location, not of the time.
The reason for this is lack of backup battery. Data is completely erased once you disconnect the main battery.
The GPS module itself has a backup battery input. Here we show how to connect an external battery to that input.
What You Need
You will need a a battery holder and a small, 3V, coin-shaped lithium battery. These can be purchased at any DIY electronics store.
I also used a piece of perforated prototyping board, but this is for convenience and not a must.
How It's Done
Below, you can see the GPS module board layout. Cut one trace as shown, and connect the two leads from the battery holder to the marked places.
Here is how the setup looks:
This is how it looks from below. Note the place where the trace is cut:
Comments
Did any body try to use this DIYdrone GPS module for Remzibi OSD?
Update:
I tried my hack on my new quad (APM1) and it seems to work like a charm. Sattellite lock in 1-2 seconds after connecting the battery! I hope it will continue to work when I flight-test it :)
Of course for new builds I would just by Jani's GPS or the new 3DR GPS, both have battery backups.
Dror
Here is the link to jDrones store. You cannot use it directly with diydrones gps, as that gps have hardwired backup power to +3.3v. If you are willing to hack your gps as shown on this post, it can be possible to use this with it too. It won't look nice looking thou..
Small update to all who has been waiting this...
Just to let you know, jD-MediaTEK backup battery trays have now arrived.
Here are first pictures of those for you all. Close up of battery tray.
As said earlier this tray can accommodate CR2032 battery that will last about 8-12 months according manufacturers information.
After you have connected everything together your GPS packet should look like this on top/left corner
Changing battery is really easy. Just push it out from other side and pull it out. Best way to push it is with plastic liner or something else less than 2mm thick non metal item.
We have tested a lot this combination, usually 3D lock times are between 2-5 seconds after power-up of GPS unit. We did even test it on inside our office building where normally we won't get any lock at all.. Now we can get lock in 10-15 seconds.
Barry no does not work. GPS needs to have constant power coming from battery. Original design feeds +3.3v to main power supply and also to backup battery supply. When you disconnect battery from your electronics all power will be lost.
On our design we have constant feed coming to GPS module and this feed is just "boosted" when main powers are on. So even if you disconnect electronics from main battery you sill have 3V backup battery feeding GPS module.
GPS module uses really low (around 10uA) current to run it's internal RTC clock. This internal RTC works with 2.0 - 4.3 voltages so average of 3V is good for it. This backup power pin MUST be connected at all times or module wont work.
Would this work?
I had the MTK updated to the latest firmware at the time (about 1 year ago), version 1.6. I don't think it has changed since. I even prepared an FTDI adapter, documented here (bottom of the page): http://code.google.com/p/ardupirates/wiki/Reload_MTek
On the APM I used the ArduPirates s/w. The ACM2 is light years ahead, of course.
Dror, any ideas what firmware you had on it?? On first revision mteks there were problem on their batteries and batteries were removed later (about 1.5-2 yrs go). Binary code has been changing few times along the years. There are update instructions on wiki.
On our tests first boot after being without power, lock takes 25-45 seconds. After that we get locks in 1-2 seconds so improvement is rather significant.
As not at office now, I had only one older test GPS set here with me with battery board soldered. PCB on picture is proto PCB and real PCB has same shape as main GPS PCB has. Battery slider out from side so replacement is easy.
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