I want to use PX4FLOW with OmniNXTF7 flight controller. This flight controller has 3.3v I2C SCL/SDA and no PullUp-resistors.

I use the PX4FLOW only with I2C port, with 5v at VCC (not 3.3v).

  1. Does PX4FLOW work with 3.3v or 5v at I2C SCL/SDA, if it is powered with VCC 5v?
  2. Are the PullUp-resistors (to SCL/SDA) of the PX4FLOW pulled to to 3.3v or 5v?

My guess is that PX4FLOW working with 3.3v at I2C SCL/SDA even if it is powered with 5v at I2C port. I added schematics, maybe someone can see if I2C is working at 3.3v if PX4FLOW is powered with 5v.

PX4FLOW v1.3 Schematic and Layout

PX4FLOW v1.3 User Manual

enter image description here

  • \$\begingroup\$ After looking at the schematic, I think the I2C SCL/SDA has always maximum of 3.3v (also in case of 5v VCC). Because the I2C SCL/SDA lines of the PX4FLOW has no PullUp-resistors. The OmniNXTF7 has also no PullUp-resistors, so I have to add it myself (each SCL/SDA to 3.3v with 2k2 resistor). PX4FLOW should be work with the 3.3v signals from OmniNXTF7, because it uses the 3.3v based STM32F4X7VX (and I know that Pixhawk with 3.3v I2C works with PX4FLOW). Can someone confirm this? \$\endgroup\$ – Sascha Jun 8 '19 at 15:03

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