This is more out of curiosity. I know that the APM2 board was a recent redesign and I was wondering why a backup battery was not provided for the GPS. I am thinking something on the lines of a micro battery like in here GPS utilizing MT3229 with micro cell Li ion battery or the hack detailed at ArduPirates.
I believe there has to be a good reason for it and would like to hear that :)
Hi Mahesh, you can add a backup battery to the MT3329 on the APM2 if you like. Check page 10 here:
I suppose this is the same discussion as this one
Note that my hack implemented the circuit referenced by Brad, yet it had problems... follow the other discussion, I am not sure at this point those problems have been solved. Should be the same for APM1 and APM2 but who knows?
Right! Thanks Dror. QATC
Any more details on the problems?
I don't see how removing a possibly noisy power line to the vbat and connecting a clean battery powered supply could cause problems?
We really should fix this problem with the GPS. How about putting a diode on the vbat line between the battery and the vbat pin and leaving the normal trace connected?
That should be simple enough and would only draw current when the APM was not supplying voltage to vbatt while letting the noisy APM line stay connected.
That sounds o.k to me Jake? but depending on what diode you use there will be around a 0.9v drop. Maybe a schottky diode? would be best..
Data sheet seems to show 2.0V-4.3V for Vbat. So a 3V button cell should do fine even with a diode.
I'll have to check what the APM is supplying, hopefully 3.3-3.6v.
If the (battery voltage - diode voltage drop) is still greater than 2v but less than the APM supply... everything should work perfect right? The battery should only discharge when the APM is unpowered and shouldn't suck up any current when the APM is on.
If you want to go the whole hog? you could make it microprocessor controlled? i.e it will only switch on when there is no current from the apm? and stay on for a set period of time, like 5 minutes? more than enough time to change batteries, or a pushbutton switch in addition that when it is pressed it gives you ten minutes of gps power before you start flying?
I was thinking about maybe a switch or some sort of connector so that you could remove it when not needed.
BUT... It looks like the current draw is very minimal, some docs suggest a 200 day battery life. Since I can get the batteries 3 for $1 at the dollar store I think it's probably not worth it to even put in a switch.
If that is correct? then yes just plug it in, I would have probably tried something by now, but only have a gas soldering iron which is far too cumbersome for the task, need a new electrical one :) But I am getting a lock within a couple of minutes and have a small 200mah 2s lipo with regulator powering the board in between changes..
Do we know if anyone has done this yet with the apm2?
I'll give it a try in a couple weeks. Right now I've got a lot going on and haven't been flying much.