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I'm very new to making drones, so sorry in advance for lack of proper terminology or if this is a dumb question. I've bound my xm+ to my transmitter (solid green light showing on receiver), but for some reason my inputs aren't showing up in betaflight. I have the correct serialRX activated on the correct UART (and have also tried both) and my receiver mode and serial receiver provider are set correctly (to serial based receiver and SBUS, respectively). This problem arose after I accidently connected my receiver to my flight controller backwards, and have already tried replacing the receiver, as I thought I might have fried my XM+, but that didn't solve the issue. Any help is much appreciated!!

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  • $\begingroup$ Initially connected backward how so? Do you mean you just switched VCC and GND or did the accidental miswiring also make other incorrect connections? $\endgroup$
    – ifconfig
    Apr 12 at 6:55
  • $\begingroup$ Which flight controller do you have? And where have you connected the receiver? SBUS can be a bit tricky on F4 flight controllers since it is an inverted protocol. It needs to be connected to a dedicated SBUS pad in that case. Did it work in this exact configuration before? $\endgroup$ Apr 13 at 9:15
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    $\begingroup$ @ifconfig I essentially turned the xm+ around when connecting. So I switched the power and the sbus connection, but the middle ground wire was still connected to the same spot $\endgroup$
    – drew.ss
    Apr 13 at 17:03
  • $\begingroup$ @Hannes Hultergård I have the JHEMCU GHF411 Pro. The configuration I currently have it connected in is the same configuration as the one that worked before. There’s a pretty clear wiring diagram for the flight controller, which I properly followed. $\endgroup$
    – drew.ss
    Apr 13 at 17:08
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Since you connected power to the SBUS pad it is possible that the inverter that sits between the SBUS pad and the UART pin on the microcontroller is fried.

To get around this, I would suggest connecting SBUS to another RX pad. However, since SBUS is an inverted protocol, you will first need to get the uninverted signal somehow. There are two ways to do this with the XM+ (other SBUS receivers have similar methods). The first option is to solder the wire that goes to the RX pad to the leg circled in red in the image below. Underside of XM+ receiver with uninverted SBUS pad circled in red source

The other option is to build your own inverter using a transistor and two resistors. SBUS inverter wiring diagram

source

The first option is probably the easiest if you feel confident enough to solder to that small pad, but it does come with an increased risk of damaging the receiver.

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    $\begingroup$ Wow! Thank you so much!!! I chose the first option and it worked perfectly. I've been working to fix that problem for weeks and your solution fixed it instantly. Thanks again! $\endgroup$
    – drew.ss
    Apr 19 at 18:16
  • $\begingroup$ I'm just happy to help. Glad it worked! $\endgroup$ Apr 19 at 18:33

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