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Old Feb 20, 2015, 03:45 AM
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Mini-HowTo
How to build an inverter cable to connect FrSky S.Bus RX with Naze

Hi guys,

Here's a little how-to on building a cable to interface FrSky's SBus on their new receivers and a naze or anything else that supports SBus on a hardware serial port. I couldn't find much on this when I was trying to connect the two, so here's a working solution.

I was hoping that since the naze supports serial RXs and SBus (at least with cleanflight), that I could just plug my X8R into my naze and I'd be away. Unfortunately FrSky has decided to invert the serial signal coming from the SBus port on their receivers, and since the serial ports on flight controllers etc are hardware based, they cannot talk to an inverted signal. This forces you to buy a FrSky cable to re-invert the signal or only use their hardware with the SBus.

I'm not a fan of ass-hattery of this nature so here's a cheap way to make your own cable. I used this $0.40 FET from a local supplier, and a cable I already had. You can use any similar FET you want, but the switching time needs to be around the 10ns mark.

The build is explained in this album. If you have any questions just ask.
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Old Feb 20, 2015, 03:47 PM
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SBus was designed by Futaba and FrSky had to use the same signal standards for compatibility with existing SBus gear. If they didn't, people would be freaking out that you had to buy their stuff and not Futaba SBus servos etc.. I suppose you could accuse Futaba of ass-hattery, but who knows, there might be a technical reason they did it. It would be really nice if future FC makers would include a pin/pad for normal SBus with an inverter to prevent the whole issue though.

If you're willing to use an X4R, there's a through-hole pad you can connect a wire to for non-inverted SBus that connects right up to a Naze no problem. I got done setting a quad up that way just a few days ago. I think a similar trick can work on the X6R and X8R, but haven't opened one up to check.

Here's a thread for the X4R. http://www.rcgroups.com/forums/showthread.php?t=2270541
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Old Feb 20, 2015, 08:23 PM
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Ahh yes I did see that X4R trick when I was looking for a way to do this, and I did open up my X8R to have a look. In the X8R there's a separate rf board which is soldered over top of the serial inverters so I couldn't use the same trick as for the X4R.

You're right, it's probably not really FrSkys fault that SBus in particular is not compatible with hardware serial ports. A jumper on FCs would be a good idea!
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Old Feb 20, 2015, 11:19 PM
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It would be nice if FrSky would make it possible to get the non-inverted signal without soldering though. Another pin on the sbus port, or something like that would be great for those FCs that don't support the inverted signal. I suspect it will become more common for FCs to support it somehow. Sbus is by far the best solution we have from a technology perspective. I know many of the newer designs do. Either with an inverted input available or a microcontroller that supports inverted serial data. As you found, it's not expensive to invert a signal.
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Old Mar 02, 2015, 03:24 AM
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I have lots of 2sc1815 and bc547 etc, with a resistor to base these should work too.
I was hoping someone had figured out a trick with the x6r like the x4r.
Maybe I'll take mine apart and have a look later.
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Old Apr 11, 2015, 05:51 PM
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Interestingly enough, the Eagletree Vector doesn't need the inverted signal. I made the cable and it didn't see any channels. I plugged it straight through and it works.

I'm using the X4R

cheers

Andrew
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Old Apr 12, 2015, 03:42 AM
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I made an inverter with the 2sc1815, it worked fine, I made no connection to 5v, simply a 4.7k resistor from RX to base , collector then connected to s.bus input on device and earth to emitter.
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Old Apr 12, 2015, 03:58 AM
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Take the ZYX-Inverterkabel from Hobbyking, its ready

Some newer flightcontrollers have the S-Bus -Inverter intern at the PCB too now
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Old Apr 23, 2015, 01:24 AM
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cool, how high does it go?
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Quote:
Originally Posted by MystX View Post
Hi guys,

Here's a little how-to on building a cable to interface FrSky's SBus on their new receivers and a naze or anything else that supports SBus on a hardware serial port. I couldn't find much on this when I was trying to connect the two, so here's a working solution.

I was hoping that since the naze supports serial RXs and SBus (at least with cleanflight), that I could just plug my X8R into my naze and I'd be away. Unfortunately FrSky has decided to invert the serial signal coming from the SBus port on their receivers, and since the serial ports on flight controllers etc are hardware based, they cannot talk to an inverted signal. This forces you to buy a FrSky cable to re-invert the signal or only use their hardware with the SBus.

I'm not a fan of ass-hattery of this nature so here's a cheap way to make your own cable. I used this $0.40 FET from a local supplier, and a cable I already had. You can use any similar FET you want, but the switching time needs to be around the 10ns mark.

The build is explained in this album. If you have any questions just ask.
Thanks for posting. Where could I buy one of these FETs? These supplier have a 8,000 unit MOQ

Thanks
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