J5 telemetry voltage tolerance

Adam Ehrmantraut

I might have missed it in the documentation but is the J5 telemetry port 5VDC tolerant?

Vinny

Hi Adam,
By default we have J5 TELEM as matching PX4 formats, with +3.3V signaling and the +5V power. We do not recommend operating J5 or any of the 3.3V based ports at 5V signaling.

There are a few things to note:

The default range of the pins in the MCU spec is a max of 3.6V
If you want 5V signaling, consider using J1 which is 5V signaling, but note the pinout is a different format by design using a DF13 connector instead of the JST-GH

https://docs.modalai.com/flight-core-datasheets-connectors/#j1---voxl-communications-interface-connector

Although the MCU claims it is 5V tolerant, there are functional configuration limitations on that tolerance that the PX4 images may include, such as internal pullups. Refer to the STM32F7 series MCU spec for details on their 5V tolerance. It is limited.
If you were to run "bare-die code" (not PX4) and meet the MCU limitations, and consequently drive inputs at 5V, keep in mind your outputs are still 3.3V based, so your 5V device you are trying to talk to (if it is a CMOS input) will not register the HIGH voltage and your interface will not work. Hence overall our recommendation is to keep 3.3V specified interfaces at 3.3V.

Let us know if you would like any further info.
Thanks!