RFD900x connection to Speedybee 405 Fixed Wing Controller

Hi, I’m wanting to connect a RFD900x to the new Speedybee_F405_Wing Flight controller. However the markings on the Fight controller telemetry port indicate one 5volt output. Am i correct in assuming I need to use level converter to connect the two as the RFD900x is a 3.3.volt device?

Yes if the levels are 5V. But usually they are not 5V

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Thank you.
I’m trying to locate more information/schematic on the speedybee board but will play it safe until then


I’m just curious.

How is the RFD900x a 3.3v device when all pins excluding the grounds are 5v tolerant here in the pin layout?

The documentation contains the following information

RFDesign RFD900x

The product page I linked above for the 900x shows 5v.

Which is correct?

In the modem kit, the manufacturer uses an FTDI adapter, which has signal levels of 3.3 V. I checked with an oscilloscope, there are signals with a level of 3.3 V.

Good to know.

Looks like RFD needs to update or revise their product page.

Just make sure you heed the warnings about power to the RFD radios. I just connected a 900ux to the Telem2 port of a cube orange+ for a quick test and forgot to turn down the power. It knocked out the can bus. Once I turned down power of the radio everything was fine (enough for the bench test). The final build will have a dedicated BEC to power the radio.

The RFD900X supply should be 5volts.
The data inputs and outputs are 5volt tolerant, however nearly all Telemetry data connections on flight controllers are already 3.3v and have been for the last few years.

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On a Cube the Telem 1 port is supplied with an separate higher current allowance, 1.5A.
Telem 2, CAN and everything else is combined into one more limited supply, 1A.

I use TX Power 27 in RFD Tools, since I’m not legally allowed to fly BVLOS anyway.

Good to know the difference. I never realized that between the two ports. Thanks! I need to install a 5v BEC anyways for this project that will have a ton of overhead, so I’ll just tap off that for the RFD radio.

As soon as I realized what was going on I dropped the TX power to 20 in RFD Tools because I knew that would get me by until the dedicated 5v supply was installed. I’ll turn it back up once I’m finished.

The high power supply for Telem1 is not widely known or well documented, but it is definitely there in the design and hardware of the Cube.


Back to the original subject, the RFD radios are tested with crazy voltages and ridiculous temperatures (true scientific terms :slight_smile: ) to ensure they are better and more reliable than the documented specs say they are.