I received a QAV-S 4" PNP quad from GetFPV today and am having an issue with it. It has a BetaFPV F405 20A aio in it.

 I have an ExpressLRS EP2 receiver bound up and plugged into UART3.  However, when I bridge the DSM and center pads, the EP2 stays solid green like it's stuck in bootloader mode, even if my transmitter isn't on.  If I remove the bridge, or bridge the SBUS pad, the receiver blinks as normal, and also gets picked up by my transmitter, but no stick inputs work in Betaflight, even though I have my receiver set up properly there. 

The only other UARTs are occupied by the GPS and Vista.



I have tried this with three brand new EP2 receivers and have the same issue each time.  what could be the issue?

A quick look at that aio fc says dsm pad should be bridged to the center.

I did notice on their wiring diagram that the pin out for uart3 plug is: TX3 (blue) RX3 (green) 5v ground.

But, then on their crossfire protocol wiring diagram they show it going tx3 to tx and rx3 to rx on the receiver, and that’s not right. Maybe try switching your tx and rx wires on your ep2 so that it’s properly going tx3–>rx and rx3–>tx?
Blue to rx on ep2, green to tx on ep2.

Good catch, thank you. However, when I do TX to TX and RX to RX, the green light blinks again and connects with the controller, but it still doesn't read inputs in betaflight. Tried reflashing the rx too, no luck.

Someone on the ELRS forum said that some UARTs "pull low" (?) which puts the EP2 into bootloader mode. I'll have to swap the GPS and RX UARTS.

EDIT: Yep, that was the issue. Works fine now. Thanks!

Ok, another issue regarding the same FC - didn't want to make a new thread about it.

Since I now have the RX wired to where the GPS was and vice versa, the GPS isn't working. I changed its port accordingly but I'm not getting anything. Could it be possible that the solder bridge on the DSM/SBUS pads is causing it? Should I just remove the bridge, period? I'm not sure if it applies only to the one UART.

It should apply just to uart3.

I could be wrong here, but I believe you want to leave dsm bridged to the center pad. That should make rx on uart3 a straight shot in- bridging it to sbus would cause rx to be inverted, you don’t want that, and leaving it unbridged would probably mean no rx connection at all.

I don’t know much about gps setup, but did you remember to set everything up in your ports tab?

(21-Nov-2022, 08:49 PM)Lemonyleprosy Wrote: It should apply just to uart3.

I could be wrong here, but I believe you want to leave dsm bridged to the center pad. That should make rx on uart3 a straight shot in- bridging it to sbus would cause rx to be inverted, you don’t want that, and leaving it unbridged would probably mean no rx connection at all.

I don’t know much about gps setup, but did you remember to set everything up in your ports tab?

Ok, I'll just leave the bridge as is.  I left everything the same as it came from GetFPV, but I only switched the GPS and RX ports, exactly as they showed.  I don't know much about GPS setup either.

I figured it out. Somehow the TX wire got pinched through. All is well.

I recently tried a DIY drone, using HEQ's drone: SWAN K1 PRO PNP, this drone has VTOL function, also provides flight control and GPS, and it only sells for $499. I put my own gopro camera in and used the HEQ battery. The flight time was about 50 minutes, and the shooting pictures were very stable.