This is a discussion of getting the PX4Flow sensor working with Copter-3.3.1 (or higher).

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Because MS5611 has kilometer-long range and tens of meters' error over time, while sonar has meter level range and centimeter level error.

There are many chinese vendors as you can see below

Because you need to know the exact distance to the surface you are looking at, and the Baro has no knowledge of that.


I have the px4flow with an integrated Sonar. I hoked it up to my PIXHAWK and choosed Sonar over I2C but still I don't get any readings. How could I test wehter the sonar data is actually transmitted over the I2C bus to the PIXHAWK?


Hi Andy,

I'm afraid we don't support using the px4flow's sonar (it's mentioned on the wiki although it may not be perfectly clear).  Paul Riseborough tells me it's technical possible to use it by soldering a wire from one place to another but I don't have details on that.  The sonar that is comes with is also very short range which is part of the reason why none of the devs have put effort into trying to get it working.

Hy Randy

uups I missed that...

So I can't use my PXFlow if I don't add another sonar to the copter:

WIKI: "Because optical flow requires good sonar/range finder data when the optical flow is enabled, an additional pre-arm check is enforced."



I hate to say it but yes, I'm afraid so.  Maybe we can get Paul Riseborough to tell us the "green wire" fix to make the sonar work as an analog sonar but the results won't be very good because it'll only work up to a few meters.

hmm ok thats bad news... So there is currently no way to use the opto flow sensor... 

When I need to add another Sonar the quad gets to bulky and its not worth the effort for just positioning hold function...

The recommended method is Lidar. It is much better than Sonar.


Is the old firmware (px4flow-klt-06Dec2014) still the correct one to use with the latest APM flight stack (e.g. Copter-3.3 or 3.4-dev) or should we use the newest firmware version from the PX4 repo?

Old one:

Newest one:

int pixhawk's terminal you can run below commands

nsh>px4flow test
then you can get below information about sonar
px4flow: ground_distance: 0.63 m
px4flow: time since last sonar update [us]: 9524010
px4flow: quality integration average : 255
px4flow: quality : 0
px4flow: PASS

thx will try this!

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