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RFD900X PPM Pass through test

Made simple test today by plugging trainer wire from transmitter, which outputs 3 volts PPM, directly to pin 15 of RFD900X.
And connect pin 15 of air unit directly to RCIN pin on PH2.1 controlling 6 servos.

Result: it worked as expected.
However, I felt a slightly more latency compared to normal receiver. It just didn’t feel as smooth.
Different radio set up might improve latency. This test is done with default settings except transmission power (100mW)

This setup should be fine for slow vehicles.

What range are you looking to go with these?

As far as my heli can go in a round trip.
10km is plenty and will be easily exceeded with directional antenna

Hi PittRBM, not easy to find samples of this type of setup. Thank you for the info.
You mean that from, let say a Taranis, I only connect PPM to pin 15 and ground to pin 16 ?

**Make sure your PPM signal is below 3.3V

Yes, you can also connect ground to pin 0,1,2.

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Has anyone tried to setup the default (failsafe) value for PPM over the RFD900x? I have been using it for control of a gimbal and had issues with the gimbal rotating (always the same way) unexpectedly.

I am assuming the this is being caused by link issues and the PPM looks like it goes to 1000us per channel which rotates the gimbal. I would like the default to be 1500us - or neutral.

I have tried using the AT&R command - just get error as response…

PPM is 8.4V ! Much too high.
Any device to reduce that ?

PPM on the RFD900X is 8.4V??? Surely not as that would fry almost anything you connected it to.

8.4V is on Taranis side. So I need to step it down to 3.3V before connecting to RFD900X.

I see.

Just use something like this:

Perfect. Thanks Marc

That’s a voltage regulator designed for powering devices not stepping down PPM signals… almost certainly won’t work for this application.

Maybe use a couple of resistors as a voltage divider for this instead

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That is what he needs if he wants to power the RFD900X from the Taranis 8.4V port. The Taranis does not have 8V PPM signals – nor does anything as far as I know. I think, or assume, that was mis-phrasing.

And surely he is not connecting any outputs from the Taranis to the RFD900X anyway. There are not any on the JR port pins.

@Marc_Dornan 8.4V is what I measure with voltmeter between PPM Pin and ground pin. Maybe I have a faulty Taranis ? And the idea is really to get PPM signal toward the RFD900X so I have only one radio for RC and telemetry. I did it before with ULRS and used this exact Pin.

I see.

PPM on the Taranis is not 8.4V!

That is the V Bat pin, or you do have an issue. Check your voltage again.
What i recommended was just a voltage regulator as I assumed you were
wanting to power the RFD900X from the Taranis.

I measured it several times. That may explain how I burned my ULRS module. Bad luck…
Edit : I also have a TH9X and I have 4.3 V on same pin. Confirmed that 8.4 is faulty.

Yep. That would burn anything.

I tested with a red led between PPM and ground pin. Led is shining normally, not burning, voltage with led drop to 1.54V.

Also keep in mind that measuring pulsed signal with a DC voltmeter will always give you lower reading than actual signal votage.

But 4.3V is definitely higher than 3.3V

You’ll need an oscilloscope or a diode and a capacitor to measure accurately.

I appreciate that this is an old thread.
Did anyone get to the bottom of what the PPM voltage is from the Taranis?
I’m currently learning how to use an oscilloscope and connected it to the PPM & ground pins on the back of my Taranis (using the pinout from an earlier post above), it appears to show the highest voltage just under 7 volts (Table on right ‘C1 (V)’).

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