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Hi,

I have already said a lot in the linked threads...

Nowadays I am flying 1,6m wing class trainers both electric and nitro. I am using my good ol' 4.0.1 Aug. nighlty DEVO 10 and walkera 1002 receivers. They fly faaar awaaay... much further than a 700 class. And they fly rather fast. Other than that, 5x 450 class helis, and a few toys (v911, v912, v922, cx-10), also no issues, since years.
On the helis I use only DSM or DSMX, either with standalone Spektrum rx or 3GX with sats / K-Bar with sats & bluetooth.

No glitches, losses so far.

That frequency deviation is a bit different - it means how much the central frequency varies to signify 0 or 1. So say with central frequency 2402MHz 0 would be marked by emitting 2401.84MHz and 1 by emitting 2402.16MHz. There is no mention in documentation that the frequency can be systematically shifted by 200KHz.

On the other hand 200KHz is 83ppm deviation at 2.4GHz. It means shitty crystal, but for module for $3-5 bucks they can easily use 100ppm crystal.

My other experiment with Beken 2421 module is even more puzzling - it holds frequency correctly, but no binding happens.

victzh wrote: I've got very strange results comparing original CX-10 (green board) TX and my own code (assembled from different sources - hexfet's Deviation module and couple of Arduino PPM modules).

CX-10 bounds on channel 2, which translates to channel frequency 2402MHz. I have HackRF Jawbreaker SDR with which I captured the signal.

CX-10 TX transmits a packet every 1.5ms with center frequency 2402MHz and width approximately 1.2MHz at -30dB which seems to be normal for 1Mbps.

My code uses nRF24L01+ and transmits packets with center frequency 2402.2MHz! and probably slightly wider in bandwidth.

EDIT : in the section 5.2 of the nRF24L01+ documention, you hade DeltaF_1M = 160Khz of deviation.... Can be set ? somewhere ?

I checked the available literature and it never mentions this 200KHz deviation.

I am not so sure about calibration of HackRF, it can be other way around- nRF24L0+ transmits on 2402MHz, and XN297 on 2401.8MHz, but other than this it's very clear difference in center frequency of 200KHz.

At 1Mbps it can easily be the reason of incompatibility of these chips, and without knowledge about "debug" registers of nRF we will not be able to compensate for it.

It would be great if someone with more precise instruments can confirm this.

Damned for 200Khz versus 2402Mhz so a deviation of 1/1000 is enough to desynchronize everything ....

Look section 5.2 of the nRF24L01 documention .... Devation at 1Mbits is 160Khz ....

I've got very strange results comparing original CX-10 (green board) TX and my own code (assembled from different sources - hexfet's Deviation module and couple of Arduino PPM modules).

CX-10 bounds on channel 2, which translates to channel frequency 2402MHz. I have HackRF Jawbreaker SDR with which I captured the signal.

CX-10 TX transmits a packet every 1.5ms with center frequency 2402MHz and width approximately 1.2MHz at -30dB which seems to be normal for 1Mbps.

My code uses nRF24L01+ and transmits packets with center frequency 2402.2MHz! and probably slightly wider in bandwidth.

I checked the available literature and it never mentions this 200KHz deviation.

I am not so sure about calibration of HackRF, it can be other way around- nRF24L0+ transmits on 2402MHz, and XN297 on 2401.8MHz, but other than this it's very clear difference in center frequency of 200KHz.

At 1Mbps it can easily be the reason of incompatibility of these chips, and without knowledge about "debug" registers of nRF we will not be able to compensate for it.

It would be great if someone with more precise instruments can confirm this.

I never found any problem flying my CX-10 with my Devo. Your issue is very strange. Are you completely sure your nRF24L01 module is ok? So, it's working perfect with another model using the same module?
BTW, what Deviation version do you have installed?

Hey all,
I've ordered the Devo 7e in hopes of modding it and flying my quads including:
Syma x5c-1
JJRC H8C
JJRC x6 tarantula
Cheerson cx-10

Cheerson CX-20 (?)


I know the module to run these quads is: NRF24L01

I have a few questions about the mod needed:

1. I was wondering though, can i desolder the X5C or H8C and use that instead, or is the NRF24L01 more universal and thus will work better?

2. if the NRF24L01 is what i need, there are several options, i need the + correct? what does it mean?

2. Do i need the PA version, to increase the range? what is the difference?

3. What is the LMA and do i need it?

Lastly, i saw this on amazon (only one with prime), and was wondering if its the +PA+LMA? the title doesn't state it but the description does list PA and LMA

www.amazon.com/Arrela%C2%AE-NRF24L01-Wir...43668&sr=8-1&keyword s=NRF24L01%2Bpa


Thank you!

Just made another test:

As I noticed the values of the registers were not what they were supposed to be at startup, I tried to set the values as in the datasheet instead of what we found in the capture... and it works, I can control the copter.

Also, it looks like register 0x1E holds a value in the nrf24l01+ (05 2B 80 00 ? not the same length than same register in xn297...), attempting to read registers 0x19 and 0x1F on the nrf24l01+ just returns a bunch of 00s.

They're not exactly the same than stated in the datasheet:
(RF_CAL is completely different)

Are you able to read the registers? If so, after power-up do they match the default values in the data sheet?

The datasheet describes them as "debug registers".

Let me know if you're thinking of other tests I could conduct, I'm running out of ideas.

Oh well, at least we can make PPM modules after a bit of butchery, that's better than nothing.

I might get a newer "CX-10A", I guess it's using yet another protocol to play with

Thanks @goebish, it clarifies the situation.

I confirm all altered parameters are required, it doesn't work anymore if I leave any of them in its default state.

can you see whether each of the differences above work indivdually, or are all 3 needed? i.e. is one of those the critical factor in connecting?

no, it definitively doesn't work with default register states, I thought it worked but that was only because I didn't reset the xn297 between each arduino firmwares tests

edit: I made a mistake with my test, in fact the CX-10 works even if we leave those 3 registers in their default state.

victzh wrote: As an experiment, can some happy owner of XN297 and working PPM module try and load stock parameters from datasheet and check whether it can control the heli in that state or not?

Doesn't work, aircraft doesn't bind with default BB_CAL, RF_CAL and DEMOD register values on the transmitter.

I also tried to have the xn297 to communicate with a nrf24l01+ this way, but it didn't work. Also tried to disable CRC, listen on other channel #, but no luck...

It is very strange. I checked the XN297 datasheet www.foxware-cn.com/UploadFile/20140808155134.pdf and though I can't read Chinese the register names are in English and all these new registers are DEMOD_CAL (0x19), RF_CAL (0x1e), and BB_CAL (0x1f) with predefined values that should be loaded:

DEMOD_CAL 0x03 0xA7 0x00 0xDF 0x0B
RF_CAL 0x95 0x2B 0x83 0x61 0xB0 0x9A 0xCA
BB_CAL 0x20 0x9C 0x67 0x84 0x7F

compare it with what happens in CX-10

DEMOD_CAL 0x03 0xA7 0xc4 0xDF 0x0B
RF_CAL 0x9C 0xAB 0xBB 0x61 0xB0 0x9A 0xC9
BB_CAL 0x20 0x9C 0x67 0x84 0x4C

These small differences can lead to frequencies slightly shifted, modulation parameters changed, and I don't know what can happen to baseband!

Almost no hope to control it with nRF24L01+. Beken on the other hand probably could be tuned if they'd be a bit more open on their "register bank 1".

As an experiment, can some happy owner of XN297 and working PPM module try and load stock parameters from datasheet and check whether it can control the heli in that state or not?

It's useful to have it in case we'll figure out what's the difference and just to document the protocol.

hexfet wrote: Annotated capture attached. Good luck

Here it is:
gist.github.com/goebish/f8982353c34f2b71ffe8
www.rcgroups.com/forums/showthread.php?t...&page=3#post31068187
unfortunately this still doesn't help for having a nrf24l01 to talk with a xn297...

Cool, I was into it, but you were faster

I'll make a capture with CE hooked up and try to code something...
updated capture

Oh s.... it's already 2am :/