In an attempt to speed up satellite acquisition, I’m planning to add a CR2032 to my Asset Tracker v2 as noted in the docs. However, the docs aren’t really newbie friendly (at least not this newbie). Can anyone provide a diagram (or a picture) of how the battery should be soldered onto this board?
But, perhaps the better question is this: If I use the external LiPo battery and have the Electron in deep sleep mode most of the time, is a CR2032 even going to be helpful? (Would waking up every 12 hours be too long of a time to benefit, since most of the satellites would have departed in that time period?)
I'd have to check the schematics, but I think the GPS will retain backup if you don't remove the LiPo for more than 3 minutes... even in deep sleep. The backup power runs the RTC in the GPS so if it has accurate time it will Warm Boot instead of Cold Boot. It will be faster, just not as fast as a Hot Boot.
And this is where the coin cell holder should be soldered to (see the CR2032 label)
When you actually have the device in hand, turning it round to see that should render "lacking documentation" a non-issue IMHO
BTW, the answer to your second part of the question is actually provided in the docs
The "main supply" in this is either the LiPo or external power or both.
Since the LiPo is connected to the Electron, "unplugging" the Electron would also mean unplugging the LiPo and even then the super cap will hold backup power for "few minutes".
And this implicitly also means, that when you don't remove the Electron the backup power won't be needed since the "main supply" (LiPo) is still connected - irrespective of sleep mode, since sleep mode
does not power off the 3v3 pin.
Thanks @ScruffR. No soldering needed of the CR2032 holder, but if you did really REALLY want to solder it on there… you’d have to cut the trace between the center pad and SC and solder a jumper from center to CC.
I guess the jumpers are named as SC (=Super Cap - default) vs. CC (=Coin Cell - optional) and these want to be used mutually exclusive.
That indeed might want to be documented somewhere.
Note that the coin cell battery only backs up the GPS fix data. None of the GPS operations are powered by the coin cell battery, other than maintaining this information in RAM.
The AssetTracker V2 has a u-blox MAX-M8Q which requires 15 μA of battery backup current when the main power is off. It doesn’t drain the coin cell when powered.
A CR2032 has 235 mAh to 2.0V, so ballpark I’d say 1.5 years if you never powered on the GPS chip, though one might ask why you are backing up the fix data in that case. If the GPS chip was powered 50% of the time, the battery should last 3 years, and so on.
I’m finding that its not always acquiring a gps fix in the time i’m allowing it to have - I’ve currently got it at 120 seconds timeout to get a GPS fix, but because it then goes to sleep for a couple of hours - it then having to basically start the whole process again and i get into a loop of never getting a GPS position.
I’m going to edit my code to give it more time if I’ve not had a GPS position to try and get something stored as i know that once its had a position - and its still in memory its quicker for it to gather its new position.
I’m hoping to get a device which is battery powered and can be sealed up for a at least 2 years… with only minimal reporting per day… I’m getting there
@medida, the ephemeris and almanac data stored in backup RAM doesn’t have a long life since the satellites are always in motion and your unit may be in motion as well. The external battery will allow for a “warm” start since the last known location is also stored. However, since you have “minimal” reporting per day, the ephemeris and almanac data will still need to be updated so a lock will take more time but it should be better than a “cold” start. You will need to experiment to see how much of an improvement it brings.
No soldering needed because there is a super cap for backup power already. If you do want to use the CR2032 you will have to cut a trace and solder the CR2032 holder.
I’ve been through the threads / docs / Github. All very informative. My new Asset Tracker 2 is working well. I plan to install the 2032 cell holder, but still have some questions after reading everything I could find:
Is there a recommended PN for the 2032 cell holder? Many varieties in the world, it seems. A photo of a correctly-installed coin cell would be most helpful, but I don’t see one anywhere.
What is the polarity of the pad? I’m assuming the center / round pad is POSITIVE, and the two outer squares are NEGATIVE, but please correct me if wrong.
What is the trace that needs to be cut, and why? Does the supercar not charge to the same voltage as the coin cell?
Any clarification gratefully appreciated. Again, I really did try to find this information before posting here and asking for your time and consideration.
Have you not got a LiPo on your Electron?
If you have
The LiPo is charging the super cap, and if you also have a coin cell connected to the same pin your LiPo (and the LiPo charging power when connected) would back-feed into the coin cell - not a good idea IMO.
Cut the default trace between the mid-pad and the super cap and solder the connection between mid-pad and coin cell.
BTW, that was already answered in this thread post #5 & #6
This should work and its makeup suggests also polarity, since the top prongs and the sides are all made of one piece of metal, so all these parts are only allowed to touch the same pole of the coin cell, consequently that must be +plus and hence the big curcular pad must be -minus - but for double checks, just measure continuity between that circular pad and the GND pads
Here’s something I’m pleased to say, which few people in life ever get a chance to hear:
“Everything you just said makes great sense. Thank you.”
The SC trace on the back of the ATv2 was so small I missed it the first time. And yes, coin cells are typically can POSITIVE, center electrode NEGATIVE. My bad. Thanks also for the PN link to the holder. I will order, install, and post pix when complete to help the general cause.
My asset tracker will be used as a ride logger for a classic motorcycle I’ve just restored. Heck, if I can install it cleanly enough, it might even be a poor-man’s LoJack. Duty cycle: the AT will be switched off for days and/or weeks at a time. I want to keep the electrical load (and data load) offline most of the time, but when I take the old girl out, I want to quickly verify GPS fix and then forget it. Both the main power and LiPo battery will have disconnect switches.
Thanks also for the PN link to the holder. I will order, install, and post pix when complete to help the general cause.
