Why would you want to ‘uninvert’ the inverted FrSky SBUS or smartport signal from your receiver? There are four different kinds of processor chips used in our multicopter flight controllers: F1, F3, F4 and F7. F1 and F4 processors are “older” processors and do not have inbuilt inverters to rectify raw inverted FrSky SBUS signals. If you want to use FrSky SBUS/Smartport with an F1 or F4 flight controller, you must uninvert the SBUS/Smartport signal coming from the receiver.
However, not all F1 and F4 flight controllers require uninversion. Many F1 and F4 flight controllers now have built in hardware inverters that uninvert the incoming SBUS/Smartport signal. Be certain to check if your particular flight controller actually requires uninversion of the SBUS/Smartport signal before making any unnecessary modifications.[vc_row_inner][vc_column_inner width=”1/6″][/vc_column_inner][vc_column_inner width=”2/3″][vc_single_image image=”1313″ img_size=”large” alignment=”center” onclick=”link_image” image_hovers=”false”][/vc_column_inner][vc_column_inner width=”1/6″][/vc_column_inner][/vc_row_inner][vc_column_text]This guide will teach you how to modify the following receivers to obtain uninverted SBUS and Smartport signal.
- X4R-SB
- XSR
- XM+
- XM
Be warned that the following modifications require very accurate soldering skills, a fine iron tip is recommended.[/vc_column_text][vc_column_text]
FrSky X4R-SB
The X4R-SB is an older model FrSky receiver and is the bulkiest on this list. The only advantages of the X4R-SB in comparison to modern FrSky receivers is that the antennas use IPEX connectors and are easily replaceable, also, X4R-SB receivers are often sold cheaply as they are outdated stock. Get the FrSky X4R-SB receiver here.[/vc_column_text][vc_row_inner][vc_column_inner width=”1/6″][/vc_column_inner][vc_column_inner width=”2/3″][vc_single_image image=”1315″ img_size=”large” alignment=”center” onclick=”link_image” image_hovers=”false”][/vc_column_inner][vc_column_inner width=”1/6″][/vc_column_inner][/vc_row_inner][vc_column_text]
Uninverted SBUS
There are a couple of different points from which uninverted SBUS signal can be tapped. The first is the middle leg of the highlighted transistor. The other is the circled pad, which is far more convenient.[/vc_column_text][vc_row_inner][vc_column_inner width=”1/6″][/vc_column_inner][vc_column_inner width=”2/3″][vc_single_image image=”1332″ img_size=”large” alignment=”center” onclick=”link_image” image_hovers=”false”][/vc_column_inner][vc_column_inner width=”1/6″][/vc_column_inner][/vc_row_inner][vc_column_text]
Uninverted Smartport
On the X4R, uninverted Smartport signal is located on the singular pin of the isolated transistor.[/vc_column_text][vc_row_inner][vc_column_inner width=”1/6″][/vc_column_inner][vc_column_inner width=”2/3″][vc_single_image image=”1333″ img_size=”large” alignment=”center” onclick=”link_image” image_hovers=”false”][/vc_column_inner][vc_column_inner width=”1/6″][/vc_column_inner][/vc_row_inner][vc_column_text]
FrSky XSR
The XSR is the successor of the X4R-SB, housing the functionality of the X4R-SB in a compact and convenient package. The XSR can be bought more cheaply than the X4R-SB although, the antennas are soldered on and are irritating to replace, depending on your soldering skill level. You can purchase the FrSky XSR receiver from here.[/vc_column_text][vc_row_inner][vc_column_inner width=”1/6″][/vc_column_inner][vc_column_inner width=”2/3″][vc_single_image image=”1322″ img_size=”large” alignment=”center” onclick=”link_image” image_hovers=”false”][/vc_column_inner][vc_column_inner width=”1/6″][/vc_column_inner][/vc_row_inner][vc_column_text]
Uninverted SBUS
Similarly to the X4R-SB, uninverted SBUS is located on the middle pin of the referenced chip on the XSR, solder to it to get an uninverted SBUS signal.[/vc_column_text][vc_row_inner][vc_column_inner width=”1/6″][/vc_column_inner][vc_column_inner width=”2/3″][vc_single_image image=”1335″ img_size=”large” alignment=”center” onclick=”link_image” image_hovers=”false”][/vc_column_inner][vc_column_inner width=”1/6″][/vc_column_inner][/vc_row_inner][vc_column_text]
Uninverted Smartport
Again, much like the X4R-SB the uninverted Smartport telemetry signal is positioned on the single leg of the circled transistor chip.[/vc_column_text][vc_row_inner][vc_column_inner width=”1/6″][/vc_column_inner][vc_column_inner width=”2/3″][vc_single_image image=”1334″ img_size=”large” alignment=”center” onclick=”link_image” image_hovers=”false”][/vc_column_inner][vc_column_inner width=”1/6″][/vc_column_inner][/vc_row_inner][vc_column_text]
FrSky XM+
The FrSky XM+ is one of the relatively newer FrSky SBUS receivers. The XM+ is much smaller than the X4R-SB and the XSR, and boasts SBUS and antenna diversity. However, the XM+ lacks telemetry. Buy the FrSky XM+ receiver here.[/vc_column_text][vc_row_inner][vc_column_inner width=”1/6″][/vc_column_inner][vc_column_inner width=”2/3″][vc_single_image image=”1320″ img_size=”large” alignment=”center” onclick=”link_image” image_hovers=”false”][/vc_column_inner][vc_column_inner width=”1/6″][/vc_column_inner][/vc_row_inner][vc_column_text]
Uninverted SBUS
To retrieve uninverted SBUS from the XM+ receiver, simply solder a wire on to the middle leg of the three pin side of the highlighted chip.[/vc_column_text][vc_row_inner][vc_column_inner width=”1/6″][/vc_column_inner][vc_column_inner width=”2/3″][vc_single_image image=”1331″ img_size=”large” alignment=”center” onclick=”link_image” image_hovers=”false”][/vc_column_inner][vc_column_inner width=”1/6″][/vc_column_inner][/vc_row_inner][vc_column_text]
FrSky XM
The FrSky XM is a smaller version of the XM+, dropping the dual antenna system to obtain its smaller stature. Like the XM+, the XM lacks Smartport telemetry. Get the FrSky XM receiver here.[/vc_column_text][vc_row_inner][vc_column_inner width=”1/6″][/vc_column_inner][vc_column_inner width=”2/3″][vc_single_image image=”1328″ img_size=”large” alignment=”center” onclick=”link_image” image_hovers=”false”][/vc_column_inner][vc_column_inner width=”1/6″][/vc_column_inner][/vc_row_inner][vc_column_text]
Uninverted SBUS
Make a solder joint at the middle leg of the selected transistor to access the uninverted SBUS signal.[/vc_column_text][vc_row_inner][vc_column_inner width=”1/6″][/vc_column_inner][vc_column_inner width=”2/3″][vc_single_image image=”1330″ img_size=”large” alignment=”center” onclick=”link_image” image_hovers=”false”][/vc_column_inner][vc_column_inner width=”1/6″][/vc_column_inner][/vc_row_inner][vc_column_text]
Conclusion
Although a singular solder joint may not seem a difficult task, making one in such close proximity to many tiny SMD components is particularly trying. Before attempting any of the modifications, assess your confidence in your soldering ability. If you would like to improve your soldering skills to be able to undertake useful hacks like SBUS signal uninversion, learn how to solder like a champion with Blair Murphy.[/vc_column_text][vc_row_inner][vc_column_inner width=”1/6″][/vc_column_inner][vc_column_inner width=”2/3″][vc_single_image image=”1312″ img_size=”large” alignment=”center” onclick=”link_image” image_hovers=”false”][/vc_column_inner][vc_column_inner width=”1/6″][/vc_column_inner][/vc_row_inner]
Thanks! I have a R-XSR and had to use the super tiny “P” pad on it to be used with a HGLRC Zeus
That’s handy to know, I’m planning on adding the R-XSR to this list once I get my hands on one. Interesting to know that FrSky seems to be clearly labelling the uninverted SBUS output on their newer receivers.
Thanks, this is a helpful guide! How does a receiver get inverted in the first place? I find it interesting that that’s a problem anyway.
Thanks!
I’m not really sure as to how FrSky inverts the signal, I believe they pass the signal through a chip which carries out the inversion process. I’m 99% sure the chip in question in each receiver is the one I’ve identified as having a leg from which the raw SBUS signal can be tapped.
Hey Collum, this is great! Well written and ultra simple compilation of the relevant information required. I’ll definitely bookmark this.
Thanks Jon! Pleased to hear it was helpful for you.
I’ve never understood why FrSky inverts their signal…
Me either, at least it’s not too hard to workaround. Still a pain though
Very interesting articLe I run inot this problem all the time and it’s very frustration next time simply mod frsky 🙂 thanks guys
Who woulda thunk it?! Great info to have. This is one of the many reasons I LOVE FRSKY products!
Try doing that with Spektrum o9r Futaba, I think not. You might be able to pull it off but they cost a lot more when you F (fudge)it up!
Great info to have! This is one of the many reasons I LOVE FRSKY products. Try doing that with Spektrum or Futaba eh?. I think not.
Even if you could do it, the cost is much higher if you F (fudge) it up!
Better is to have soldering iron with controllable temperature. Uncontrolled irons may become too hot and peel fragile receiver conductors and pads off. And don’t forget about R-XSR receiver here!
By the way for all X4R/XSR line now there are F.Port too.
sorry if im a little slow, just started with frsky and still figuring it all out. i just got the xm+ and have to invert it because i have a omnibus f flight controller. i was curious about the soldering. do we just solder to the middle pin instead of the sbus pad?
For us new folks, this is a critical question. An affirmative reply seems logical but no mention above. ‘Simply solder a wire to the middle (circled) pin’.
Hello
an idea for the rx4r?
thank you
Im waiting too , my rx4r ; https://imgur.com/a/i1wVrwL
Hello i stripped sbus pad on my rx4r reciver , please help images below
https://imgur.com/a/i1wVrwL
This may turn out to be the final obstacle to getting my hexcopter flying!
FrSky, you led me a merry chase.
I have an older PixHawk clone, FrSky RX8R Pro Receiver. I only learned today
about this whole inversion issue. Has anyone found the hack to get non_inverted
signal from RX8R Pro?
I opened mine and had a look. Found some interesting clues :
Four thru-hole pads labeled Neg, SB_N, SB_O
Fourth hole is square and not labeled.
This is on the side nearest the SBus Out pins.
There is another similar set of four pads near the Smart Port pins.