DIYDrones Magnetometer issue resolution



It's a long story that I will try to summarize. The latest revision of the magnetometer that had some design improvements including making it easier to manufacture to boost production using the pick and place machine, but that also came with a weird issue. 

When I was developing the APM Oilpan we had some noise issues on the 3.3V line caused by a missing 200K resistor on the Voltage Reference pin on the 5V side of the I2C translator (obviously this board never saw the light), if you don't populate this resistor it will introduce terrible noise on the line and cause the analog sensors to fail, this bug was found by Jose Julio (Thanks!). 


A curious thing is that the first version of the magnetometer didn't have this resistor (it worked fine anyway), in the second revision i tried to do the right thing and follow what the datasheet suggested so I added the 200K resistor (same that caused terrible issues on the Oilpan because we didn't use it), expecting some improvement. 


When the boards arrived from the fab, we assemble some and they appeared to be fine, Cindy (our testing lady) added the observation that the sensors were slightly noisier, but we didn't listen (Sorry Cindy!). For the pressure of months of long waits we just released the boards. In just matter of days we received tons of complains.   


After days trying to solve the problem we finally discover that the 200K was the issue. The 2nd issue we have discovered but is not critical is that the voltage regulator will not perform well if you don't suck enough current from it, the magnetometer uses very, very low power and the best practice to solve this is to add a 200 ohms resistor from the 3.3V to GND to add enough load to it (Thanks to Nathan Siedle for this trick), we are not doing this right now, so you will see a power supply output of 3.7V, but the performance is perfect. 


All new boards have this fix, but for those who already got affected boards I would like to give a sincere apology to all our custumers and I would like to offer two resolutions to this problem:

1.- Send it back and we will repair it for you. We will cover all the shipping expenses. Please contact custumer support for more info: help[@] 


2.-Repair it yourself (DIY) quickly and safely by following the following instructions.


NOTE: Before you repair your board, check if your board has a resistor marked "204". This means it has not been fixed (see the first two photos of the repair steps for reference), and if you see instead a resistor marked "0" your board is fine.

If you choose to repair it yourself and something gets messed up, you cannot then return the board. If you are unwilling to take this risk or are feeling a little uncertain about your soldering ability, do not do this. Just return the board for replacement.























1- Locate the 200k resistor, it is marked with "204."























2- With a soldering iron, heat either of the resistor's solder points
and wait a few seconds for the heat to reach both solder points. Weak solder irons may not work very well. 
























3- Without applying too much force as no not damage the pads, gently
nudge the resistor with the tip of the soldering iron. 
























4-The resistor

should stick to the tip, so just lift the tip off the board to remove
the resistor.























5- Make sure you the pad are still there. 























6- To create the solder bridge place the tip of the soldering iron
over both pads and apply enough solder to brigde the pads.
















































7- If the solder ball is touching both pads then your are done. 


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  • I purchased two of these magnetometers.
    The mag worked at first, and the next day it generated a continuous near-zero heading.
    I assumed it was killed by static from my tupperware body, and purchased a second.
    Same thing happened. I still have both, and will try the fix on one.
    I'll let you know if it works.
  • Developer

    It just causes poor performance. But it should work... If the board is "defective" could be just an isolated board with issues.


    You should ask for RMA for a replacement...

  • Is the presence of the reistor causing poor performance, or does it simply not work? I ask as my newly received mag is not working. I'm happy to perform this modification if it will fix the problem. However if it turns out something else is the cause, will the fact that I have "tampered" with my circuit prevent me from getting a replacement?

  • Developer
    The Sparkfun board is fine, it doesn't have I2C translator (so you don't suppose to use it in 5V), so the board is except of this issue.
  • Developer
    @SId that is normal, those pads are connected together and the solder loves to short those out, but is perfectly fine.
  • Developer

    Just wanted to note that if you are at all uncertain about removing the resistor, don't bother - just cover it in a blob of solder.  Be careful not to bridge to any of the pads on the nearby IC, of course.


  • I bought the rev 1.1 magnetometer just a month back...And since then I did not fly yet..But I have soldered it to the OilPan and APM and uploaded the AP_COMPASS_TEST code and found that the reading given were fine...
    So is there still any need to remove the 200K resistor and bypass it as shown in the tutorial ?..Or if I remove it and bypass then it will work better...

    Can someone please explain me...
  • thanks..


  • 3D Robotics
    sorry, I misunderstood your last post, this fix should be the only modification that needs to be done!
  • what other mod is needed ? SOmething is still left after the resistor and jumper mod ?



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