Pixhawk 4 - I2C sensors not found


Our Pixhawk 1 which was initially in our BR2 died 2 weeks ago. So I ordered a brand new Pixhawk 4 to replace it (PX4 FMU V5).
Everything seemed to work, I could control our ROV again. :grinning:
But there is a problem, I would like to connect I2C sensors but they are not recognized. I tried with 2 different Bar 30 sensors which were working great with the previous pixhawk (and on an Arduino, I re-checked to be sure).
Q ground control keeps saying : “no pressure sensor”.
Nothing in mavlink inspector and SCALED_PRESSURE either.

I tried to downgrade the Ardusub firmware. didn’t work.
I tried to externaly power the sensor. didn’t work
I tried to change GND_EXT_BUS. didn’t work

My question is : am I the only one to have problem with I2C and PX4 ? Does someone also experienced that ?

I found different threads on the forums, like this one but it doesn’t really help.

Should I try to find a pixhawk 1 ? :neutral_face:
thanks !

Hi @Guillaumeee,

Hi Eliot,

Oh sorry I didn’t see that thread, my apologies for that !

I will try it and keep you posted.

Thanks !

Well, I tried 4.1.0 and 4.2.0, with 2 different Bar 30 sensors, and the PX4 still doesn’t find the sensors …
And there is something else weird : if I upgrade the firmware by USB, then connect to the ROV with the tether, I can control the ROV. But if I disconnect everything and re-connect with the tether, I will only have the video. No more control to the vehicule.
Anyway. Do you, at Blue Robotics, still provide first generations of pixhawks ? It might be easier.
thanks !

Are you able to confirm/set the following parameters?

Parameter Value

Not certain what’s happening there, unless there’s a missing connection somewhere when you reconnect things.

We provide them in our full electronics enclosures, but because they’re no longer manufactured (and haven’t been for some time) there’s a significant shortage of them, so we’re unfortunately not able to provide them as a separate item. We’re working on our own alternative that should be available within the next few months, but there’s not a fixed release date for that yet.

Hi Eliot,

First of all, thanks again for your help.

I set the parameter BARO_PROBE_EXT to 768 and it works now ! I found my BAR 30 sensor.
So it is possible to use the pixhawk 4 with ardusub 4.2.0 dev.

Now I also added a celsius fast response temprerature sensor on an I2C splitter but I don’t receive any values. Nothing in temperature(3). I only have the T° value from the BAR 30 in temperature(2).
Do you have any clue ?

For the other problem, it’s OK, when I only have the video and lose the control/telemetry, I restart the computer and it works.

Good to hear :slight_smile:


I can replicate that here. We tried setting BARO_EXT_BUS = 3, which got the Celsius to work but stopped the Bar30 from working. Wouldn’t suggest trying it - it’s not simple to get back the other way.

We’re looking into this, but not sure how long it will take to fix. It may just be a parameter issue, but may also require changes to ArduSub - we won’t know until we have a working solution.

Glad you’ve at least got a workaround. A few notes:

  • If you’re restarting the topside computer perhaps there’s some kind of firewall issue or something.
  • If you’re restarting the onboard computer, does the mavproxy service come up in the web interface?
    • If it does then it might be sufficient to reboot the autopilot (from the web interface).
    • If it doesn’t then you can likely reboot just the onboard computer (from the web interface) rather than having to power cycle everything.

By the way, I’ve just re-read your initial post and seen that you got a Pixhawk 4 because your initial Pixhawk 1 (from us) failed. If you haven’t had your BlueROV2 for very long then it might be worth contacting support@bluerobotics.com - they may be able to send you a replacement. Pixhawk quantities are very low, but if we’ve sold you a product that didn’t perform reasonably then that’s on us to fix.

No problem, it’s not a big deal.
We will follow that. We also bought a Pixhawk 2.4.8, we will give it a try.

By restarting the topside computer it works. By restarting the onboard computer too. And yes the mavproxy service comes up in the ardusub companion web interface. So indeed I can have access to it and restart it this way.

Thanks but we bought our ROV in 2018, made a lot of improvements, and the pixhawk died because of a leak. Fortunately everything else is ok.

Again, thanks a lot for your help !

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This problem has now been raised in a GitHub Issue (including a temporary workaround), which can be followed for updates/fixes :slight_smile: