Last step from rfd900 modem + PPM to the GCS via Bluetooth rather than via USB cable

Sorry if I posted this out of place, I researched wiki and forums but still cant find answer to my question.

  • Is it possible to make the last connection from a rfd900 modem that uses PPM passthrough to the GCS via a Bluetooth device, rather than via a USB cable?
    The usb cable works beautifully - however its a cable and it limits my freedom of moving around at ground position. I can put a very long cable from my RC transmitter to the rfd900 unit - but it seems much wiser idea to do it wirelessly (via BT).

I can not be the first person here?
My question, can it be done? If cant - then perfectly happy to find other radio solutions :slight_smile:


You could use a Bluetooth serial adapter. I’ve used these to test serial connections but have never used one for for any extended amount of time.

IOGEAR Bluetooth Serial Adapter, GBC232A

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Thank you both for the replies.
Yes, I read both those post with delight some time back.
I have it set up according to your illustration (less the Frsky, I have another radio).
But from your post I was not sure if you really succeeded or not, since you asked about adding a USB cable connection as well. Anyway got confused there.
Now, very pleased to understand you got it to work!

For me, it still do not work. MP on Win10 machine fail to connect via the HC06 BT unit.
However, I studied the wiki one more time, and think I missed to uncheck the ‘Reset APM on USB connect’ box, and also to check the SPP com port box is checked and that the com port properties for the BT unit has correct speed.
I will check that tomorrow.

For your USB question, Why not power the RFD unit from pin 4 instead of pin 5 and then you solder on cable connectors from a USB cable?
Only TX and RX pins will have two wires connected, should work.

I am sure now I have done all, according to the wiki after more than triple checking.

But still something prevents the MP to connect via BT HC06 device to the ground based RFD900 unit and onwards to the remote rfd900 and the flight controller.
I have tried three different BT units and all pairs fine and parameters set fine.

Since you got it to work its just a matter of finding the issue.
I see from your picture you have a RFD 900x and I have a RFD 900+ unit.
are they different in this respect? needs other SW settings or cant do it at all?
What do you think?

The BT unit seems to connect, steady red LED and then goes blinking again and finally the connection times out.


Success :grinning:
Finally got it to work, thanks to Moreton at support at RFDesign.
It was a faulty Bluetooth unit, tricky since it seemed to work but something was wrong with it.
Now all works as expected, its great!

If anyone do not want to fiddle around to set this up, they have a new product that do pretty much the same thing

Hi Karl,
would you mind to share your practical expertise on sending rfd900 telemetry to a handheld device (android phone) via bluetooth? I’m running an RC submarine: Futaba 40 MHz RC - PixRacer FC - rfd868x telemetry - Windows 10 laptop - QGC groundstation). I cant switch to the rfd txmod module you mentioned because my RC gear is not compatible and I need to stick with the 40MHz band for radio control of the submerged sub. Receiving telemetry data via bluetooth link between windows PC and android phone running QGC would provide some flexibility in moving around the pond weile running the sub.



Hi Theo,
Not much of expertise but some practical experience at least. This is how I would set it up. Make a little box with the rfd868x unit you have on the ground side, together with its own 5V power supply and connect a bluetooth HC 06 unit to it. The box can be placed higher up for good reception. Then you can connect your Win 10 laptop running QGC using the laptop’s built in bluetooth OR you can connect with your android phone’s QGC. But this way you can not connect both phone and laptop at the same time.
Would that work for you?

Hi Karl,
thanks for your very quick reply. Your system satifies all needs - it fine to have QGC running either on the PC OR on android. Before I give it a try, would you mind if I ask you a few questions which might safe me time and nerves?

Is the rfd firmware version critical for setting it up? If so, which one worked for you ?

How did you wire the rfd and the BT modules? VCC & GND is clear. Is it TX to RX and RX to TX? Or TX to TX and RX to RX?

Did you leave the key and state contacts on the BT module blank?

Do I need to flash the BT module with a specific firmware ? If so, which one?

Did you install specific BT drivers on your windows PC? Or do the generic win 10 driver(s) work “out of the box”?

I will give you feedback once I get it to work.


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Yes, know what you mean, can easily get stuck on some one detail for days.

Don’t think so, since its working for you now and the serial link is a basic function.
I have a RFD900X unit but I understand the manual is the same as for your RFD868X. My firmware version is 2.53, I think.

Manual say the default settings for Serial connections are:
57600 baud rate • No parity • 8 data bits • 1 stop bit
So I use that for setting for the BT unit as well as the PC/Phone/Tablet QGC settings as well. Its got to be the same across the link.

RFD-TX wired to BT-RX
RFD-RX wired to BT-TX

Now, here we are moving in to deep waters.
I think the reason you are asking is because you have a BT module HC-05 which can also act as a Master. That unit has 6 pins. I really never got success with these units. You need to press and hold the thing marked EN (or short them if no key is present on unit) on most units but not all, while booting up to make it enter in to config mode. I never made that work.

Its more easy to use the HC-06 unit with 4 pins that can only act as a slave. Then you don’t need to worry about that.

I think you don’t have to but if it doesn’t work then you may need to research.
Here is a version number that works with the BT unit configurator I use, BT_CONFIG.EXE, seems to be 2019.09.01
You can get it free on the internet, but scary download sites are around. If you need I can upload it to you.

Also, this is the connection you need to do from your Win10 machine to the BT unit to configure it with a Name, Password and communication speed (57600).

No, all these units work out of the box: Win10, MacBook Pro, Android for Samsung phone, and for Android Samsung tablet. For Raspberry Pi 3 and 4 it works fine after installing a Serial package sw. All connect as a breeze, most times. The most failing to connect is with the Win10 - those guys never get it right. Need to reboot etc etc.

Hope it helps
Good luck!


you can get the BT unit in to the same box as the RFD unit if you squeeze it a bit.

Hi Karl,

I appreciate your detailed and structured reply very much (!). This is going to be a real time saver I guess.

Thanks a lot for taking the time to assist my efforts.

All the Best,


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Hi Karl,

thanks to your advice everything worked out straight. I have QGC running on both - PC & Android phone!


All the Best!


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