Single-Board Universal Module

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15 Mar 2015 13:19 #29734 by SadSack
Replied by SadSack on topic Single-Board Universal Module
Well hope next week or so I'll have my tools out and should doing something useful.
Which switch are you using now?

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15 Mar 2015 16:26 #29746 by PhracturedBlue
Replied by PhracturedBlue on topic Single-Board Universal Module
I'm using a Peregrine PE42641 on recommendation, and it seems to fit the bill.

After further experimentation, I'm getting a nice strong signal out of the CYRF, CC2500 and A7105 chips. the NRF is being detected, but I'm not getting any RF out of it. This is he same result I got on the 0.9 board (except the switch now works) , so there is likely either a design issue or a software issue.

The board is also not very consistent, the RF chips do not always initialize on power-up.

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16 Mar 2015 02:22 #29753 by PhracturedBlue
Replied by PhracturedBlue on topic Single-Board Universal Module
NRF24L01 is working now too with a nice strong signal. I had forgotten to setup the CE pin. I need to do some careful experimentation to see how the range is, but the board seems fully functional at this point. I'm still concerned about not getting a reliable detection on power on, that too needs more debug, but the board should be good enough that I can put it in a Devo radio and try it out now.

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16 Mar 2015 13:23 #29759 by Fernandez
Replied by Fernandez on topic Single-Board Universal Module
Good news !

Maybe off topic, out of curiosity, but more and more radios seem to get two tx antennas on the Tx module. I am wondering how it works? Is it diversity, for reception of telemetry back from model?

and if you designing new state of the art concepts, must it also contain 2 antenna?

Here example the cheap flysky i10 opened.
Attachments:

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16 Mar 2015 13:45 #29760 by PhracturedBlue
Replied by PhracturedBlue on topic Single-Board Universal Module
Got me.
On a receiver you may choose to have 2 antennas and to run them perpendicular to each other to maximize signal strength. On a transmitter I'm unsure what you'd need 2 antenna for. Maybe in a telemetry system you could have dedicated Tx/Rx antennas, or a differential setup, or in the case of video, having a 2nd transceiver. Also, maybe MIMO, though I dunno if it actually makes any sense in RC or not. Short answer is that I'm not an RF expert, and have no idea what benefit they get.

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16 Mar 2015 15:57 #29761 by Wene001
Replied by Wene001 on topic Single-Board Universal Module
In Case of the Spektrum DX18 transmitter the manual says:

Dual Diversity Antenna
The DX18 is the first Spektrum transmitter with a “dual diversity” fixed antenna. Aside from being incredibly durable, it’s the first pro-class transmitter antenna to employ the use of both vertical and horizontal antenna arrays. The horizontal array is cleverly housed in the handle on the back of the transmitter and, with the vertical array, virtually eliminates the possibility of polarization blackouts.

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16 Mar 2015 16:04 - 16 Mar 2015 16:04 #29762 by vlad_vy
Replied by vlad_vy on topic Single-Board Universal Module
Spektrum use not the best solution for that, it simply frequently switching both antenna by RF switch.
Last edit: 16 Mar 2015 16:04 by vlad_vy.

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18 Mar 2015 05:39 #29809 by PhracturedBlue
Replied by PhracturedBlue on topic Single-Board Universal Module
I have significantly reworked the Multimod code to support the UniversalTx board and merged all the changes that have happened in the past 6 months. It will likely take several days to test the new code to ensure the multimod is still working properly and I didn't break anything else. Hopefully I'll have the Multimod workinginside a Devo radio by this weekend.

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18 Mar 2015 06:19 #29811 by FDR
Replied by FDR on topic Single-Board Universal Module
Are wou aware of the mod somebody made to improve the detection of the modules?
If I remember well it was about the nRF module...

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18 Mar 2015 13:49 #29827 by PhracturedBlue
Replied by PhracturedBlue on topic Single-Board Universal Module

FDR wrote: Are wou aware of the mod somebody made to improve the detection of the modules?
If I remember well it was about the nRF module...


There was a code change I heard about that helped. I thought it was already in the trunk. If there was a physical mod to the board, I didn't hear about that.

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18 Mar 2015 19:21 #29837 by FDR
Replied by FDR on topic Single-Board Universal Module
I was talking about the code change, but I don't know if it is in the trunk...

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19 Mar 2015 00:08 #29856 by mwm
Replied by mwm on topic Single-Board Universal Module

FDR wrote: I was talking about the code change, but I don't know if it is in the trunk...


I know we got at least one such mod into the team trunk.

Do not ask me questions via PM. Ask in the forums, where I'll answer if I can.

My remotely piloted vehicle ("drone") is a yacht.

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19 Mar 2015 00:48 - 19 Mar 2015 00:48 #29862 by hexfet
Replied by hexfet on topic Single-Board Universal Module
It's in there. Was putting an "ifdef EMULATOR" around it when working on SymaX.

Seems like a good time to finish my multimodule.
Last edit: 19 Mar 2015 00:48 by hexfet.

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21 Mar 2015 23:50 - 22 Mar 2015 00:47 #30023 by octagon
Replied by octagon on topic Single-Board Universal Module
2.4GHz antennas can be very small and the TX cases are usually RF-transparent, if not loaded with carbon-black, or metalization, so internal antennas should be OK.

Adding a second antenna for receiving RX in full duplex makes sense, but as these chips alternate between TX and RX (TDD) the use of separate RX and TX antennas makes no sense unless separate RF and TX chips are used, which of course would be OK, but is probably not the case.
This leaves the use of two antennae for diversity, which could be OK, especially if the model transmits an RSSI message, which could be used by the TX to decide which antenna to be used.

(Reportedly, external antennae is marketing "requirement" as most people will not buy a TX without something pointy sticking out.)

A 25x25mm ceramic patch antenna (WLP.2450.25.4.A.02) on a 50x50mm ground-plane could also work.
A little bit of gain won't hurt as most people will be facing the model under control.
Last edit: 22 Mar 2015 00:47 by octagon.

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22 Mar 2015 16:07 #30048 by Fernandez
Replied by Fernandez on topic Single-Board Universal Module
Myself I use with good succes PCB J-pole antenna at TX.
This antenna has a good wideband match, I have it aligned horizontally.

Many of the small NRF modules use a "folded" j-pole, I use just the non folded.

like this one;
www.dx.com/p/repair-parts-replacement-in...i-32562#.VQ7oHsstFtY

Should be no reason not to implement pcb antenna, as long as the pcb antenna stays clear, un obstructed.

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22 Mar 2015 20:14 #30069 by PhracturedBlue
Replied by PhracturedBlue on topic Single-Board Universal Module
FYI, getting the UniversalTx running with a Devo radio is proving more difficult than expected. I've been struggling with stupid stuff like getting SPI slave mode to work (which I've never used before). I did find that I need to cut th A7105 MISO line (I dunno why I put it there in the 1st place), and I now have read operations working properly (I never did get it working with interrupts, but DMA seems fine). Something is still holding the MISO line, and I haven't figured out what it is yet, so the board won't respond back to the Devo Tx right now. Also, the usb detect still doesn't work reliably for unknown reasons. I need to pull the BOOT0 jumper most times to prevent entering the bootloader in normal mode. I don't get it. The pulldown resistor should be sufficient to prevent the need for that.

Anyhow, progress is being made, just slower than I'd have liked.

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22 Mar 2015 21:19 #30075 by octagon
Replied by octagon on topic Single-Board Universal Module
So goes product development! Never easy or a straight line, surprises etc happen.
Thanks for the update.

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23 Mar 2015 19:14 #30124 by PhracturedBlue
Replied by PhracturedBlue on topic Single-Board Universal Module
I finally got the Devo transmitter to detect the universalTx. Lots of code issues, but in the end, the ISR handler is just a lot slower than I expected. I've already rewritten the critical part in assembly which gets it down to 12 cycles from the time the CSN pin arrives to setting it on the corresponding rf chip (+ another 12 cycles for the interrupt handler to start). I would expect that to be 24 cycles or 0.5us. It looks like it is closer to 1us though. For some reason even though the MCU says it is running at 48MHz, it seems like the actual core clock is closer to 31MHz (measured by executing a fixed # of nops and measuring the delay with my Saleae).

Oh well, that should be fast enough. I just need to optimize the ISR because it is taking way too long to process switching commands. I really expect the utx to be faster than the multi-module, but even with the higher clock rate, the ARM instructions are not as efficient as the AVR for I/O

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23 Mar 2015 20:16 #30131 by vanwadiver
Replied by vanwadiver on topic Single-Board Universal Module
PB: Your progress reports are exciting, and as many others on the forum, I am following your progress with great anticipation.

A thought has been kicking around since your post a week ago (#29717) in regards to potential sale/purchase of a universal transmitter once development and testing is complete. Referencing your comments about FCC regulations, and the fairly strict rules against selling ‘unlicensed transmitters’, I’m wondering where that line exactly is... In other words, how much of a ‘mostly assembled’ board could be sold, purely as a ‘hobby item’, before it becomes an ‘unlicensed transmitter’? Could enough of a board be manufactured and sold as a ‘hobbyist kit’ where a marginally (and I do mean marginally) skilled person could complete the final assembly?

I’m hoping there is some middle ground between a low likelihood of success if I were to attempt to place and solder all of the components, and the complete pain of FCC certification of a commercial product.

Either way, whether my thoughts are completely off track or not, your progress and success is definitely awe inspiring!

Cheers,
Paul

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23 Mar 2015 20:42 #30132 by PhracturedBlue
Replied by PhracturedBlue on topic Single-Board Universal Module
As I thought about this more, I realized there is another option I hadn't really thought through:
If the module is sold primarily as a JR/PPM module with an enclosure and antenna, it could be certified by the FCC. Devo folks would be able to remove the module from the package and install (and thus take any risk of FCC violation on themselves, just as they do with any RF mods today). Of course passing FCC compliance would probably cost $10k (if we get it right the 1st time, or more if we fail). I am not sure I could drum up enough of a market to cover those costs.

As far as your question of how-much assembly is 'enough': Here is whatSpark-fun says:
www.sparkfun.com/tutorials/398
In the end, the rules are not clear enough, which means the risk is too high for me to take on personally. Perhaps starting on LLC would help, but I'm not really sure you can start an LLC as the sole purpose to shield yourself from something you know may not be legal. Honestly, I don't want to find out.

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