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Devo 7E NRF24L01 installation

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17 May 2018 16:08 #69280 by sier
Devo 7E NRF24L01 installation was created by sier
Hi everyone,

I could use some help with debugging. I removed the stock module from my Devo 7E and installed a NRF24L01.
So far so good. The transmitter has no errors when starting up, I assume that means the module is recognized.

The problem is, I can't bind to my Silverware quad. I have a T8SG with the same model file, which binds instantly.

I triple checked all connections with a multimeter, it all looks fine. I usually know what I'm doing, but I'm feeling a little out of my depth here.
How do I debug this? What else can I check?

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17 May 2018 20:07 - 17 May 2018 20:08 #69284 by sier
Replied by sier on topic Devo 7E NRF24L01 installation
Progress!

I disabled the PA, and after that managed to get a single bind. After that the binding failed again. It feels rather random.

What I noticed while I was bound is that the telemetry signal strength was around 1%. And I failsafed constantly.

I have no experience to diagnose what could cause these signal strength issues. Bad solder joint? They all look good, and multimeter continuity checks out for all of them.
Last edit: 17 May 2018 20:08 by sier.

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18 May 2018 12:03 #69295 by sier
Replied by sier on topic Devo 7E NRF24L01 installation
Another update on this:

I re-enabled the PA and can use the module relatively reliably at 300uW. So I suspect this is an issue with the on-board LDO not being able to supply enough power.
I will install a AMS1117 power regulator and report back.

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18 May 2018 13:21 #69297 by aMax
Replied by aMax on topic Devo 7E NRF24L01 installation
Sounds to me more like a wiring problem.
I had this kind of NRF module for a long time beside an A7105 and the CYRF in my 7e.
How did you bind the CE pin, via resistor or straight to VCC?

Devo7e, TaranisQ X7, 4in1 MM, Futaba FC18plusV3.1/DFT/FLD-02

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18 May 2018 13:27 #69298 by sier
Replied by sier on topic Devo 7E NRF24L01 installation
It’s connected straight to 3.3V

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19 May 2018 12:31 #69317 by sier
Replied by sier on topic Devo 7E NRF24L01 installation
Latest update:

As aMax suggested, the AMS1117 didn't do anything.

Next thing I did was to remove the long wire connecting the CE pad with VCC, and bridge the pads directly on the NRF module with a tiny wire. If I read the telemetry correctly, that only reduced reception quality.

Next I build a ghetto RF shield using cling wrap and aluminum foil. That did two things. It allowed me to go up to 30mW (I lost bind at 100 mW), and it introduced so much noise to the signal that the model became uncontrollable (even on 300uW). So I removed the shield again.

Suggestions guys?

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19 May 2018 13:43 #69320 by sier
Replied by sier on topic Devo 7E NRF24L01 installation
One more:

I soldered a 20k resistor between CE and VCC. That improved things a lot. I also put back the ghetto RF shield.
It's not as good as my T8SG was, but it's ok now.

Maybe someday I'll desolder the 4in1 module from my T8SG and put it into my Devo. But that's for another time.

It's good enough. I'm calling it a day.

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