<![CDATA[VOXL2 J19 external I2C not showing clock activity]]>Hello ModalAI Support,

I am trying to use external I2C on a VOXL2 M0054 through J19.

I checked the hardware side and found:

  • J19 I2C lines sit high at about 3.3V when idle
  • continuity from J19 to my external board is good
  • ground connection is good

However, when I try to access the external I2C buses from the VOXL, I do not see any clock activity on the J19 I2C clock pins with an oscilloscope. The lines remain at steady 3.3V and no external device responds.
From the documentation, my understanding is that:

  • J19 pins 4/5 are the external magnetometer I2C path
  • J19 pins 7/8 are the spare external I2C path
  • the J19 I2C path goes through a TCA9517 level shifter/buffer

Could you please advise:

  • Whether I should expect visible clock activity on these J19 pins when accessing the external I2C buses?
  • Whether any additional configuration is required to enable the J19 external I2C path on VOXL2 M0054?
  • Whether this symptom suggests a known issue with the J19 / external I2C buffer path?

I can provide more details if needed.
Best regards
Joel

]]>https://forum.modalai.com/topic/5300/voxl2-j19-external-i2c-not-showing-clock-activityRSS for NodeTue, 30 Jun 2026 13:42:30 GMTMon, 29 Jun 2026 16:01:29 GMT60<![CDATA[Reply to VOXL2 J19 external I2C not showing clock activity on Tue, 30 Jun 2026 13:09:26 GMT]]>Hi @Eric-Katzfey

Yes, mainly via PX4 / qshell, and I also cross-checked once from Linux userspace.
I tested both J19 I2C paths:

  • pins 4/5
  • pins 7/8

With both methods I could not communicate with the devices on my custom PCB, and on the oscilloscope the SCL lines stayed flat at 3.3V with no clock activity.
So it looks less like a device/address issue and more like the J19 I2C lines are not being driven out to the connector.

Do J19 pins 4/5 and 7/8 require any additional enable/configuration on VOXL2 before they can be used for external sensors and whats the preferred way to access them?

]]>https://forum.modalai.com/post/26279https://forum.modalai.com/post/26279Tue, 30 Jun 2026 13:09:26 GMT<![CDATA[Reply to VOXL2 J19 external I2C not showing clock activity on Mon, 29 Jun 2026 19:01:55 GMT]]>@saegsali But how were you trying to access the I2C? What software? Via PX4?

]]>https://forum.modalai.com/post/26274https://forum.modalai.com/post/26274Mon, 29 Jun 2026 19:01:55 GMT<![CDATA[Reply to VOXL2 J19 external I2C not showing clock activity on Mon, 29 Jun 2026 17:59:33 GMT]]>Hi @Eric-Katzfey

We have a custom PCB which we use for different sensors e.g. to measure temperatures. The board is tested with an Arduino where it works with I2C.

I now used the same PCB and connected it to the I2C lines on the J19 plug (4/5) and (7/8) but with neither of these I was able to establish communication to the I2C chips on the PCB. I then analyzed the SCL lines (pins 4 and 😎 with an oscilloscope and realized that no signal is present there.

Therefore I was wondering if any additional configuration is needed for using J19's I2C lines with external sensors?

Thank you in advance!

]]>https://forum.modalai.com/post/26273https://forum.modalai.com/post/26273Mon, 29 Jun 2026 17:59:33 GMT<![CDATA[Reply to VOXL2 J19 external I2C not showing clock activity on Mon, 29 Jun 2026 16:09:40 GMT]]>@saegsali How are you trying to access the external i2c buses on J19?

]]>https://forum.modalai.com/post/26272https://forum.modalai.com/post/26272Mon, 29 Jun 2026 16:09:40 GMT