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Why Does OTG Increase Range
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JohnRaggio
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It seems like there is little debate as to OTG helping to increase range.  I don't yet have a controller or OTG cable, but am trying to get my head around the whole thing.  This comes after reading a bunch on the web and watching a ton of videos.  I headed down this rabbit hole after unsuccessfully trying to get my old Nexus 7 tablet to connetc to the Spark.  My iPhone 6, iPad mini 2, and Google Pixl all connected fine.  Turns out the Spark sometimes uses 5.8 GHZ for its wifi and the Nexus 7 only supports 2.4.  
Anyway, back to my original question, why does OTG help with range?

My understanding of facts
  • Remote Control will use 2.4 or 5.8 to communicate with the Spark.  Whichever of these is not used is then available for the RC to Smart Device.  The RC will essentially have two wifi connections, one to the Spark and the other to the device.
  • 2.4 has a greater range than 5.8, but 5.8 has improved video streaming capabilities
  • Some android devices can't use 5.8, such as my Nexus 7 and some Android devices in Europe are prevented from using certain 5.8 channel ID which means that they sometime fail to connect or even see the SSID or RC or Spark when flying without RC and connecting directly

My theroies as to why OTG improves range - all may apply?
  • Since some android devices are unable to connect to the RC using 5.8 they hog the 2.4 for their needs leaving the lesser range 5.8 for the RC to Spark connection
  • By using the OTG the smart device can be put into airplane mode, reducing local interference withthe wifi connection to the Spark form the RC
  • Because the RC now nly has one active wifi conneciton to the Spark it also has no interference on this single connection


As an aside the wifi settings in the DJOGo app are only configuring wifi connecton with the Spark (between the RC and the Spark, or between the device and the spark when controlling with device alone).  There is no way to configure the wifi between the RC and the smart device, correct?  That conneciton wil just end up being whichever one the Spark is not using?

This is my first post here.  I've been chatting a little on a Reddit board and a Facebook group for Spark owners.  I like those since they are mobile phone friendly, but figured I'd try the official forum tonight.  Any other good boards you guys use?

Thanks,
John




2018-1-20
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SOUNDWAVE439
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We all know how to reason well. You are one hell of an intellect mate
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JohnRaggio
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SOUNDWAVE439 Posted at 2018-1-20 22:00
We all know how to reason well. You are one hell of an intellect mate

Not sure I follow.  Sorry.  Are you agreeing with my theories?  Am I understanding this correctly?
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JohnRaggio
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Bumping this in hopes of getting a response. There must be some benefit given the higher end models ship with a cable.
2018-2-12
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Locationscout_Bavaria
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In my mind, it´s s a psychological range extension with OTG on Android. You trust this bird a lot more and that encourages you to fly farther.
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JohnRaggio Posted at 2018-2-12 05:39
Bumping this in hopes of getting a response. There must be some benefit given the higher end models ship with a cable.

The reason why you didn't get the answer is because there are literally dozens of threads about it and people are tired about writing the same thing over and over.

In the EU the extended range is totally real. Simply from a fact that 5,8GHz channels Spark uses are forbidden under the CE regulations and no android phone ment for the EU can use them. Also, the allowed power of 5,8GHz band is 20x lower than in the US. Thus without the OTG cable you cannot use the 2,4GHz band for RC-Spark and range without it is ridiculously short (about 50m in my case versus 400+m with OTG cable).

As to the other countries (under the FCC regulations) some people have the same problem as we do in the EU (probably EU market phones), others notice large input lag, some suttering in the transmitted video and other problems concerning double WiFi connection. Even in this cases the OTG cable is a great way how to improve the quality of flight and pilots confidence.

You are correct that there is no other way how to set the WiFi channel except the DJI GO 4 App and one band is always between the Spark and RC and other between the RC and phone.
2018-2-12
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rimza
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Video latency is one of the main improvement between WIFI and OTG connection. The real bummer is that IOS version of DJI Go 4 allows OTG connection between RC and device.
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Vyborny83 Posted at 2018-2-12 06:24
The reason why you didn't get the answer is because there are literally dozens of threads about it and people are tired about writing the same thing over and over.

In the EU the extended range is totally real. Simply from a fact that 5,8GHz channels Spark uses are forbidden under the CE regulations and no android phone ment for the EU can use them. Also, the allowed power of 5,8GHz band is 20x lower than in the US. Thus without the OTG cable you cannot use the 2,4GHz band for RC-Spark and range without it is ridiculously short (about 50m in my case versus 400+m with OTG cable).

My Huawei mediapad T3 (android) which also operates as a phone ONLY works on 5.8ghz. If i switch the Spark/RC to 2.4ghz with my iphone my Huawei can't even see the RC's wifi anymore, which is annoying!
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bjr981s
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Your logic is sound. And your research correct.

You did hit on why your range is better and always will be with an OTG cable. Only 1 wifi connection to the controller.

Here is some further information you may find useful

Wifi operates like an old home network hub, it is shared media. Not like a modern network switch thats a switch and does not share the media.

All the devices on a wifi network have to share the air media on the same channel. That means that they compete with each other. It uses basic ethernet protocol that deals with collisions when more than 1 device tries to talk at the same time. But the signal strength of the Smart device that is inches away from the RC device will swamp the aircraft as it gets further away.

Using an OTG cable just eliminates the requirement to share a channel. You still however have to compete with other wifi devices that are using that channel that are in either proximity to the RX transmitter or the aircraft. You can see your aircraft for get interference close to you then clear up as it moves further away. That means that a Wifi base station is most likely underneath operating on the same channel.

Wifi on startup tries to find a channel that is not in use. This is negotiated when you power up the aircraft. Unfortunately that is great for the TX but not so good for the aircraft. The aircraft will roam into territory that has base stations on the same channel.

Most wifi home units are on automatic and will choose the channels in a specific order. If you fix your aircraft to a channel at the other end of the order list you will get less interference.

I see lots of people doing videos on comparing with and without OTG. None of these that I have seen are valid as it is impossible to replicate what is happening on the airwaves over multiple flights as you fly away from yourself over dense housing.

To do an accurate test you would need to go out into the desert far away from all radio interference.   

Cheers



  

  
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Vyborny83
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MKPSG12 Posted at 2018-2-12 06:59
My Huawei mediapad T3 (android) which also operates as a phone ONLY works on 5.8ghz. If i switch the Spark/RC to 2.4ghz with my iphone my Huawei can't even see the RC's wifi anymore, which is annoying!


That's because that 5,8Ghz you see is between the RC and the Spark. The tablet you have connects to the RC via 2,4GHz. If you change the channel to 2,4Ghz (between the Spark and the RC), you would need a device capable of comunicating at 5,8GHz with the RC and since your tablet cannot use this band you cannot see it. Just as I wrote above. And I agree, it is really annoying that DJI still did not fix the OTG.
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eYeSkYeYe
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Showtime!!

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JohnRaggio
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Thanks all for the insights. I know there are many discussions on otg, but I never found one that explained why. I assume I should also disable WiFi on tablet to reduce interference?  Same goes for phone ?
2018-2-12
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Yank61s
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I had a similar question a few weeks ago about the OTG cable and got a response from DJI saying that they don’t support using the cable. Any thoughts as to why?
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BeastMaster_101
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Nice post, I can agree with your theories as I think the same. However, one other thing could   be that since the RC has to only have one wifi connection, it leaves it to have more power rather than splitting the RC's power to 2 difference connections. This just what I think, it could have no difference what so ever but thats my thought on it.
Happy Flying!
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bjr981s
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JohnRaggio Posted at 2018-2-12 11:29
Thanks all for the insights. I know there are many discussions on otg, but I never found one that explained why. I assume I should also disable WiFi on tablet to reduce interference?  Same goes for phone ?

You should disable wifi and Bluetooth. Also if you wear a smart watch. Turn it off.
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bjr981s
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JohnRaggio Posted at 2018-2-12 11:29
Thanks all for the insights. I know there are many discussions on otg, but I never found one that explained why. I assume I should also disable WiFi on tablet to reduce interference?  Same goes for phone ?

You should disable wifi and Bluetooth. Also if you wear a smart watch. Turn it off.
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heliman
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I’m pretty sure the rc has has two radios. One for 2.4GHz and one for 5.8GHz.
Do they affect each other in any way? Not much, I think.
Is there any proof that latency is greater through wifi than through usb?
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rimza Posted at 2018-2-12 06:33
Video latency is one of the main improvement between WIFI and OTG connection. The real bummer is that IOS version of DJI Go 4 allows OTG connection between RC and device.

Yep, this sums it up for me...video latency (or lack off beyond 70 metres) issue is resolved by OTG.

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Vyborny83 Posted at 2018-2-12 07:12
That's because that 5,8Ghz you see is between the RC and the Spark. The tablet you have connects to the RC via 2,4GHz. If you change the channel to 2,4Ghz (between the Spark and the RC), you would need a device capable of comunicating at 5,8GHz with the RC and since your tablet cannot use this band you cannot see it. Just as I wrote above. And I agree, it is really annoying that DJI still did not fix the OTG.

That makes sense, and explains why in the manual it says that 2.4ghz has a shorter range than 5.8ghz, but everyone says they get better range with 2.4. . I think it should become forum law to specify whether people are talking about the RC-AC frequency or the RC-phone!! That also means that half the time when people are referencing which band they're using they actually talking about the opposite one!
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MKPSG12 Posted at 2018-2-13 00:49
That makes sense, and explains why in the manual it says that 2.4ghz has a shorter range than 5.8ghz, but everyone says they get better range with 2.4. . I think it should become forum law to specify whether people are talking about the RC-AC frequency or the RC-phone!! That also means that half the time when people are referencing which band they're using they actually talking about the opposite one!

what frequency do i see in dji 4 app on my phone????
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Vyborny83
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mali Posted at 2018-2-13 01:28
what frequency do i see in dji 4 app on my phone????

If you mean the number in the right upper corner of DJI GO 4 App, you see the frequency between the RC and the Spark
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Vyborny83 Posted at 2018-2-13 01:30
If you mean the number in the right upper corner of DJI GO 4 App, you see the frequency between the RC and the Spark

yes that one,because in numerous reviews they say that is video link frequency
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bjr981s
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Yank61s Posted at 2018-2-12 15:43
I had a similar question a few weeks ago about the OTG cable and got a response from DJI saying that they don’t support using the cable. Any thoughts as to why?

I will answer your question but the response was rejected.

With a Your Fill has band Information.. Never seen that before. It may be that the message was too long.

I am going to break it down into multiple replies. Hopefully it will work or at least identify what is being rejected as bad information???

   
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bjr981s
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DJI Support OTG. Unfortunately most of their support staff are not fully skilled in all the technology they support.

Also most Users / Pilots are also in the dark.

Physical Layer

OTG. Is a poor description of a normal USB cable that has a Mini / Micro/ Micro-C. Host end. But is has been used as a label to sell USB cables that are not USB Type 1 PC to peripheral cable.

Leaving out USB 3 and USB-C for the moment. (They complicate things as they have 2 TX and 2 RX wires.)

A USB Cable has 2 ends a Host End and a Peripheral End. The only differentiation of the ends is that the TX wire and RX wire are reversed at the connectors. (The wires cross over in the cable. The TX becomes the RX at the other end.)

So the pinouts are different at either end.

Normally the host end has the big rectangular USB type 1 connector and the peripheral end has a Micro or Mini USB connector.

So it is easy to determine which is the host end in which is the Peripheral end.

When you have a host USB port that has Micro or Mini USB you need the port to be wired as a Host with TX and RX on the correct pins at both ends of a USB Micro / Mini to USB ? peripheral.

The Mavic Pro and the Mavic Air uses a Micro to Micro cable where the host end and peripheral end is identified by having the host end with a 90 degree connector.

So the Provided DJI cable for Mavic Pro and Air is in fact an OTG cable. (On The GO or micro / mini host port.) A terrible marketing name.

The Spark has a USB type Micro host port. It was included in the Spark RC controller to provide connectivity to the DJI Goggles. As the Goggles have a normal Micro Peripheral port and are supplied with a USB type 1 to USB Type Micro charge and data cable. It would have been dangerous to provide a USB type 1 rectangular connector like the Mavic Pro. As using the supplied cable would have reversed the RX and TX pins.

So their solution was to provide a Micro USB Host connector on the TX and Sell a OTG cable for the Spark.

This OTG cable they sell has a USB Type 1 Female Peripheral connector. (To mate with the normal USB cable host connector supplied with they goggles.) and a USB type micro host connector. So it double crosses the internal wiring so to speak.

So do DJI support an OTG cable for the SPARK? Yes, Yes, Yes they sell one identified by them for the Spark.

But it doesn't end there.
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bjr981s
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Link Layer.

There is a protocol for USB Peripheral Device to Host communications. The peripheral provides data about itself so the Host. e.g. PC can load the correct device drivers.

In this case the Link Layer is the Aircraft FW and either IOS, Android, or DJI Goggle.

This link layer is Supported by DJI and is generic across the range. It provides the transport for the App layer. For at  least Android, (DJI Crystal Sky Monitors), DJI Goggles across Spark, Mavic Pro, and Air.

The specific wording on the DJI website is concerning about android/ for non CrystalSky and IOS SmartDevices. Suggesting they still have some work to do. But will do the work.

The CrystalSky mounting bracket purchase page advises that the Bracket works with the Mavic Pro and Spark but you need to buy the optional DJI OTG cable (part link provided) for Spark operation.
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Application Layer.

The application Layer has 2 ends. The App / FW in the Device and either the DJI Goggles or the DJI Go 4
Application.

Now this is where the issues surface for the Spark.

There is a fundamental difference between the Spark and the Mavics on when the FW in the device looks for a USB insertion.

The Spark Firmware as of this date 13 Feb 2018 has an issue in the link layer as to when it looks for the insertion of the USB connection.

The Mavics will recognise that the USB device is inserted and connected if you power up any device in any order.  Aircraft, TX and Smartphone connection. It is always looking and will recognise it is connected. It does not need to see the insertion take place.

The Spark will only recognise that the USB is inserted, If it is inserted after the TX is bound / Linked to the Aircraft.

If it has been inserted prior it will ignore that it is plugged in.

This is also an Issue for the DJI Goggles and they Spark. I went through a support procedure with DJI and this is the recommendation from them.

The Issue is that if you use the DJI Goggles they will work (Vision) but the spark with have reduced range. i.e. operating as if no Smart-device is connected. (30 Metres height and 100M distance restriction)

You must first connect your IOS or Android device to the Spark (Wireless) as if you are going to fly it with that. Once the Spark has recognised it has a smart device connected insert the Goggles OTG and disconnect the Smart-device. You can only have 1 video display active at a time.

This connection timing issue causes more issues for IOS than it does for Android.

Hence OTG on Android (Particularly Crystal Sky monitors. I love them, I have all 3) is a lot more stable than IOS. Apples OTG peripheral support is quite demanding.

OP I hope this further clarifies and assists your research.
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bjr981s
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For those of us that use OTG most or all of the time. Due to the timing of when you insert the OTG cable, the window for the FW device version check for the transmitter, is bypassed.

If you update your Spark by using the Assistant app on your PC or Mac, you can end up with Mismatched FW with your TX unit. If you do a FW update from Assistant, reboot the Spark then do a WiFi connection to the Spark, and let it check and update the TX if required.
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bjr981s
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Other Pilots, I hope, if you have waded through this d-i-s-s-e-r-t-a-t-i-o-n, that you can see you will have more success if you insert the OTG cable on the Spark after the TX has been linked to the aircraft.

And that DJI are not abandoning us or turning off OTG Spark Support, but have some issues to solve for us to achieve 100% reliable OTG support.

Cheers Brian

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bjr981s
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My goodness snookered by a disallowed word.

The Word Was D-i-s-s-e-r-t-a-t-i-o-n

I wonder what that means in Chinese.

Apologies for the breakup of the post to find this.
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JohnRaggio
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Thanks, bjr981s. I read it, but need a second pass for sure. What you wrote was interesting, but did not address the original question. Why is it that people claim more distance with otg?  Did my theories make sense?

I have read elsewhere that the order of connection was critical. I connect RC to AC, cable to iPad, cable to remote.

Lastly, for fairly short flights is it even worth messing with the cable.

Thanks
John
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JohnRaggio
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Whoops, just read thread again on bus and see that you had answered my original question, bjr981s. My mistake. Thanks again for taking the time!

John
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JohnRaggio
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rimza Posted at 2018-2-12 06:33
Video latency is one of the main improvement between WIFI and OTG connection. The real bummer is that IOS version of DJI Go 4 allows OTG connection between RC and device.

Rimza - why do you say it’s a bummer?
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Vyborny83
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JohnRaggio Posted at 2018-2-13 04:05
Rimza - why do you say it’s a bummer?

He is probably referring to a fact that iOS devices work again with an OTG cable (though still unofficially) while on android the OTG is still broken (almost 3 months by now...). Ironically the iOS devices actually see the 5.8GHz band (unlike the Android) and therefore it is not as crucial for them. Though the improved latency and other advantages of a cable still applies as well.
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bjr981s Posted at 2018-2-13 02:39
DJI Support OTG. Unfortunately most of their support staff are not fully skilled in all the technology they support.

Also most Users / Pilots are also in the dark.

Totally wrong in at least 3, 4 places.

Anyway, TL; DR and correct explanation:



Just Sense pin shorted to the ground at Host side. (that's why direction of OTG USB cable matters).
As more tech savy reader will notice, there is no TX, RX in USB standard. I guess TX/RX were very poorly chosen synonyms for D- and D+ lines. But even than, it makes no sense. No "crossing" of any kind.... D+ ends in D+ in both connectors, and so does every other single pin.

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bjr981s Posted at 2018-2-13 02:42
Application Layer.

The application Layer has 2 ends. The App / FW in the Device and either the DJI Goggles or the DJI Go 4

*The Spark will only recognise that the USB is inserted, If it is inserted after the TX is bound / Linked to the Aircraft.*

If you are claiming that USB OTG connection between the RC and Android device can be only made when RC is linked/bound to AC, that's totally wrong.

Everyone invited to do it like this:
1. Forget about AC, it's not needed, lol.
2. Turn on your Android device, plug peripheral side of the USB OTG cable into it.
3. Start DJI GO 4
4. Turn on RC and wait till it boots.
5. Plug host side of the USB OTG into RC

Voila.... device-RC connection made.... it will say Aircraft disconnected on the top, but it's clear that RC-device connection works. Once AC is turned on and bound to RC, you'll get video feed from the AC.

There is some timeout after the RC booted, in which RC is sensing for OTG presence and stops to bother once timeout expires, tho.

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JohnRaggio Posted at 2018-2-13 04:05
Rimza - why do you say it’s a bummer?

No OTG for android. YET??
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eYeSkYeYe Posted at 2018-2-13 07:50
Totally wrong in at least 3, 4 places.

Anyway, TL; DR and correct explanation:

Thanks For your input.

It was naughty of me using RX and TX. But most People understand  Transmit and Receive. rather than D1 and D2.

Can you show me the pin outs Both ends of an USB- Micro to USB -Micro.

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eYeSkYeYe Posted at 2018-2-13 08:11
*The Spark will only recognise that the USB is inserted, If it is inserted after the TX is bound / Linked to the Aircraft.*

If you are claiming that USB OTG connection between the RC and Android device can be only made when RC is linked/bound to AC, that's totally wrong.

Try that on IOS and see what you get.
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bjr981s Posted at 2018-2-13 22:42
Thanks For your input.

It was naughty of me using RX and TX. But most People understand  Transmit and Receive. rather than D1 and D2.

Here you go.



So, on host (A) side, it's sense (ID) pin shorted to ground, on peripheral side (B), sense (ID) pin is floating (not connected).

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bjr981s
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eYeSkYeYe Posted at 2018-2-14 00:57
Here you go.

https://i.stack.imgur.com/sfE9Y.gif[/img]

Thanks that will let readers see the complete picture. I should not have tried to oversimplify things.

Can you confirm your experience with Android and the timing of the OTG connection?  

You did do it on a Spark and not a Mavic?

The Mavic is fine as I posted. Its only the Spark I have issues with. I have tested 5 sparks on IOS multiple devices. Crystal Sky all 3 models and 5 other androids. I cannot get it to connect if the TX is not connected to the aircraft.

IOS will beep and advise that the Peripheral device may not be supported but then works. If plugged in before the link is established nothing happens. No Beep no work.

Cheers


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