Hi,
What is max value for (APM1+HMC5843 V2.0 + AC3.1) MAG FIELD during ARM Check ??
Wiki says it’s 330 for APM1, but in video Randy says it’s 530?
6. Verifies Adequate Compass Magnetic Field Strength: (APM1/APM2 about 330, PX4/Pixhawk about 530)
And which unit this value actually is? Is it raw (Gain and offset corrected?) magnetic field strenght in mG(milliGauss)??
Regards
Jani
It’s 330 for the APM1 and APM2. At the time I made that video it was 530 but we reduced it later. In any case a few people complained and we changed it to 330. This means <115 or >544 will fail the pre-arm checks.
Ok thanks Randy!
It’s more clear now. I looked Motors.pde and found how the check is done.
Reason i was asking is because after updating my old APM1 + HMC5843 compass from 2.91b to AC3.1stable i got mag field warnings and couldn’t arm without disabling compass check. My compass is external with pylon and haven’t got any problems before. However i checked my tlogs from now back to year or two ago and i can always see magfield values around 600, offsets are below 100. I even took compass module out off the quad and test it in separate arduino board with quite similar results.
Now i have 2 options on my mind:
A. There might be a problem in my compass. I Checked local raw compass values in few different places with different hmc5883l board + arduino and got lower readings. Also noticed that my 5843 board has some problem with 3.3V regulator, it is outputting about 3.5V which is too high. I have to look at it more.
[size=85]B. As i live in Finland and we are known to have (strong?) magnetic field in vertical direction (Z-axis) and mag field strenght in my location is around 53uT (530mG) i wondered if this is part of the problem " being on the upper edge of limits".[/size]
EDIT: Looks to be some kind of hardware problem with 5843. I tried with chinese 5883L board and mag field after live calibration was 310-335 
Too bad this board doesn’t have I2C level shifter, maybe too risky to fly with this. Is it verified that AC3.1 should work ok with 5843, if i’m right there’s nothing big difference in setup between 43 and 83L except Gain and sensitivity?
Regards
Jani
I think 3.5V is probably fine. When the 3.3V regulator outputs 5V there’s a real problem but 3.5V is probably ok.
So I think the problem here is that the 5843 outputs a larger value so that’s upsetting the pre-arm checks. You know that in AC3.1 you actually have the option of disabling only the compass check? Go into the mission planner’s Standard Params page and set Arming Check to “Skip Compass”
Jani,
Before the 3DR GPS/Compass I used a HMC5983 module with integrated reg from eBay with more than excellent results (asun Valkeakoskella, Tampereen lähellä) on a modified APM2.5. That should work with your APM1 too. But I agree with Randy. The datasheet for the 5883L says 3.6V is max. and 4.8V is absolute max. for supply voltage, so 3.5V should be fine.
T:Stefan