DJI has released its 2.4G Full HD digital video downlink, the DJI Lightbridge

[flitelab]

Thanks. I have learned more -- spent the past hour or so running the system and looking at S.Bus to PWM converter output on the oscilloscope. Here is what I know so far:

(1) The input to the Lightbridge ground unit accepts a Y cable with the ability to connect to two radios. This works just fine. On the air side, the PWM signals from the pair of radios is encoded into S.Bus and output through a single two-conductor cable.

(2) Air side S.Bus (DJI calls it DBUS) encoding is standard and you can decode it with a Futaba SBD-1 S.Bus decoder. This means you can use the Lightbridge with any system, controller, servo, or gimbal that can accept S.Bus or PWM. To get PWM you just need an air-side S.Bus decoder with PWM output. The only limitation is that you don't get OSD video overlay without a DJI controller. To be clear, on the control side this system has no limitations that require a DJI flight controller or gimbal. All channels are accessible over standard S.Bus and any of the 16 channels can be converted to the usual PWM output and simply plugged into anything that accepts PWM.

(3) The first radio (red plug on the ground side) is encoded into the S.Bus stream with channels 1 through 8 on the radio side matching channels 1-8 on the air S.Bus. The second radio is encoded with channels 1-8 mapped to 9-16 on the air side S.Bus. You cannot assign higher channels on either radio. The trainer port must be set to 8 channel output. Each radio is effectively an 8-channel radio. A single radio operator has 8 channels -- no more.

So, as you guys have been trying these out over the past few months, has anyone tried to map a channel in the A2 higher than 8? Or have you tried setting your radio trainer port to anything other than 8 channels? I can't believe I'm the first guy to notice this, and that makes me think I am wrong about something. However, having spent the evening playing with the control output and looking carefully at channel mapping on an oscilloscope, I am confident the above listed results are correct. What I am hoping is that somehow I am missing something with the trainer port to Lightbridge connection -- that maybe there is a setting on the radio, for example, that will allow more than 8 channels. So far, all I can get to work is the function described above.

FYI to anyone following this: With minimal documentation and only a few hours working with this I am learning in real time with plenty of uncertainty involved. My views may change as I learn more.

Thanks for the info and research. Maybe we can develop a work around with a decoder. Odd that DJI couldn't provide this ability directly.

 

[flitelab]

Do you think this would do the trick?
http://www.fpvmodel.com/rmilec-high-precision-pwm-ppm-sbus-signal-converter-v2_g478.html

On further reading it only does 10 channels on sbus conversion. So you wouldn't be able to get more than 2 from the second set of 8 from LB for the gimbal channels I suspect.

 

[kloner]

gh4 has an option to output 1080p to the hdmi, it does not change anything in the rest of the cam, still rolls 4k internaly. the 4k is for the external recorders and you guys with zen aint gonna be swinging that anytime soon

 

[flitelab]

Ok thanks. I thought I had read it only output at the record level so that at least is good. I guess however it wont work with the Zenmuse AV converter since it required interlaced apparently.

 

[kloner]

good grief....

 

[econfly]

Do you think this would do the trick?
http://www.fpvmodel.com/rmilec-high-precision-pwm-ppm-sbus-signal-converter-v2_g478.html

On further reading it only does 10 channels on sbus conversion. So you wouldn't be able to get more than 2 from the second set of 8 from LB for the gimbal channels I suspect.

It should work, but I have not used that decoder myself so I can't say for certain. Keep in mind that you can use multiple decoders. Just break out the signal cable (Y cable, etc.). You can even split off one or more cables for decoders and still feed s.bus into a main controller.

 

[flitelab]

The issue with that decoder though is it only does the first 10 sbus channels. So you can't get at all 8 of the gimbal ones.
You would need a programmable one so as to grab the 9-16 channel range.

 

[econfly]

The issue with that decoder though is it only does the first 10 sbus channels. So you can't get at all 8 of the gimbal ones.
You would need a programmable one so as to grab the 9-16 channel range.

Check out the Futaba SBD-1. It's not cheap, but you can program it to pull out any S.Bus signal. This is what I have been using to test the Lightbridge S.Bus output on the air side, where I was able to find out that channels 1-8 from from the first radio and channels 9-16 come from the second tethered radio.

Just a practical note -- any air-side S.Bus decoder(s) will need power. No big deal, but plan for a 5v supply from somewhere.

 

[RCedit]

Sorry, want to make sure I'm following. To be clear, the 5.8G radio requirement only pertains to untethered 2-man op, right? If tethered there's obviously no frequency interference issue and no reduction of channels available. Am I right?

 

[econfly]

Sorry, want to make sure I'm following. To be clear, the 5.8G radio requirement only pertains to untethered 2-man op, right? If tethered there's obviously no frequency interference issue and no reduction of channels available. Am I right?

Yes.

 

[flitelab]

Sorry, want to make sure I'm following. To be clear, the 5.8G radio requirement only pertains to untethered 2-man op, right? If tethered there's obviously no frequency interference issue and no reduction of channels available. Am I right?

Tethered 2 man only offers up 4 channels for the gimbal if your using an A2. If your using a WKM it isn't even possible without the 5.8 radio.

 

[econfly]

Tethered 2 man only offers up 4 channels for the gimbal if your using an A2. If your using a WKM it isn't even possible without the 5.8 radio.

Not quite right. True, you can move four channels through the A2. But, you can also split the S.Bus out from the Lightbridge, send one output to the A2 (or WKM) and the other output to an S.Bus decoder. That allows you to use, say, channels 1-7 for the WKM and use the S.Bus decoder to send 8-16 into a gimbal (Zenmuse or anything else that accepts PWM inputs).

As things stand, the only impediment is that you have to be tethered with two radios on the ground. Lightbridge only gives you 8 channels per radio, but with two tethered radios you can 16 channels to work with in the air and you can split them up any way you want with S.Bus decoders.

 

[flitelab]

Not quite right. True, you can move four channels through the A2. But, you can also split the S.Bus out from the Lightbridge, send one output to the A2 (or WKM) and the other output to an S.Bus decoder. That allows you to use, say, channels 1-7 for the WKM and use the S.Bus decoder to send 8-16 into a gimbal (Zenmuse or anything else that accepts PWM inputs).

As things stand, the only impediment is that you have to be tethered with two radios on the ground. Lightbridge only gives you 8 channels per radio, but with two tethered radios you can 16 channels to work with in the air and you can split them up any way you want with S.Bus decoders.

Yes sorry I was referring to using the setup stock as DJI intended, not with the decoder work arounds.

 

[soler]

Hi Guy's

I have a working prototype of a decoder that I have made and which will address some of the issues you have here, The decoder is accepts a S.BUS input and then maps the channels for output correctly to the zen

Inputs
S.Bus

Outputs
Sbus - Un Modified Signal ( Like a Y Cable)
Sbus1 - Modified Channel Mapping to fit the ZEN S.bus input
Sbus2 - Modified Channel Mapping for the ZEN
PWM - 4 outputs to assignable channels

For the channel mapping what it does is resign the higher channels to the correct input for the ZEN, it also splits and mixed some channels so that one switch controls the video and the photos saving an extra channel, when left in photo mode it will continue to take photos without have to flip the switch for each one (you can of course still do this)

Channels will be configurable via a PC interface.

Let me know if this is something of interest and if you would like to see more features. As I said I have a working prototype that I am using now.

Thanks

 

[flitelab]

Definitely interested. Any pictures of it so far?

 

[soler]

Definitely interested. Any pictures of it so far?

Just a little black box at the moment, I have it housing a second receiver, but this will be removed from the production units. I will post some picture and a screen shot or two later.

 

[soler]

Definitely interested. Any pictures of it so far?

Hi Flitelab,

A couple of pictures for you, The SBUS+ is under the FrySky Receiver, The green light is signalling the fail safe status.

There is one wire from the receiver to the SBUS +, One wire from the SBUS + to the Zenmuse controller. This is operating on a single TX. On the TX it is using channels CH10, CH11, CH12, CH13 and DG1, the SBUS + Then maps these to the correct Channel for the Zen as you can see from the screen shot.


I have just ordered another batch of PCBs, and the next version will be smaller but with a greater number of outputs.

View attachment 18103
View attachment 18105

 

[Jumpy07]

Soler, I am interested in one if you are making a few..

 

[soler]

Hi Jumpy, I will PM you wen they get closer to being ready,

After this first run I will see who much interests there is producing a bigger batch.

 

[maxwelltub]

So there is nothing stopping anyone from using this with other gimbals right? I hate the idea of being tethered to my camera operator as sometimes I need to move to get a better line of site of the multirotor.