Matek F405 SE - Wiring with pins

ArduPlane Plane 4.1
1

First, HAPPY NEW YEAR !

I used to mount all my builds with pins and no soldeing for Rx, GPS, DJI fpv…
After looking at the wiring on the Matek site, it is specified that the Rx crossfire must be put on Tx1 Rx1.
For the F405 SE ,these pads are under the FC and I would like to know if I can change the UART and take for example Tx4 Rx4 which is on the top of the card ?

So I would like to put Crossfire on Tx4 Rx4 - GPS on Tx3 Rx3 - DJI Fpv on Tx2 Rx2

Sorry for my bad english, I hope my explanantions are clear.
Thanks for your help.

2

Your English is perfect, but unfortunately I can’t help with your problem :slightly_smiling_face:

3

Thanks Stewart :blush:
It doesn’t matter if you don’t have the solution

4

The reason they say use TX/RX1 is because that is the only port with DMA. Meaning it’s the fastest port. You could try one of the others but you may be getting errors or telemetry issues with the crossfire system. I seem to remember reading something that the latest firmware solves that issue but if the CRSF is acting up then you may need to move the port. If you are just using CRSF, and not doubling up it up with CRSF and MAVLink then it may be less of an issue.

5

Hi Allister. Thanks a lot. I don’t know what is DMA, I ve seen DMA enabled is required and if it’s just an issue with some errors of telemetry, I could accept this :slight_smile:
I m using now Express LRS instead of TBS crossfire but I ve readen it s the same protocol.

So I will try another pins for the Rx. Thanks again

6

If you use ExpressLRS, then you should definitely use a DMA capable UART for it. This is even more important with ELRS than with Crossfire.

7

DMA is Direct Memory Access. It is some hardware in the microcontroller that allows it to do things without needing the processor to perform the work. For UARTs this generally means the message is sent to a queue by the processor and then the DMA performs the handling of the transmit and receive data from the memory to the peripheral hardware without the processor having to be involved constantly. This frees up the processor time (a finite resource) to do other more important tasks. This is also usually done when the processor is not using the memory so it doesn’t even slow down the processor.

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8

Thanks @cambull it’s clearer for me. Do you think if this function is not used, so if I plug my Rx on UART2, it could be dangerous for the flight ?

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I am not sure how the firmware is structured or what the processor load is in your particular situation. It shouldn’t mean the flight computer loses control of the aircraft, but I suspect it could mean that the data stream out of the UART might be sometimes a bit broken up if the FC gets busy on other higher-priority things. This may or may not affect the crossfire port communications.

Perhaps somebody else with direct experience with this can chime in?

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Thanks @cambull
Yes if anybody has already used other uart for Rx on a F405 SE, it could be usefull…

11

That was from a Matek F405 Std or CTR. I also had a few random radio failsafes at very close range (sub 100m), even though I had just been flying about 600+m.

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Thanks @Allister . A close failsafe should be dangerous for me. So I will try to build it on the Tx1 Rx1 without pins. I m not use to solder wires on the FC .

13

Please another request.
Why on the matek website, on the wiring scheme appears CRSF plugged on Tx2 Rx2 ?

14

Might not be an issue for Betaflight or Inav. Matek’s own Ardupilot instructions to call out TX1/RX1 for CRSF. Honestly, I’d just stick with that. You’re going to need to solder to the board to get to the ESCs anyhow.

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