SBUS problem on custom autopilot hardware

PX4 Autopilot
1

Hello, I have designed my own autopilot hardware that is compatible with standard and related to this pinout table.

While testing my new PCB I have found that the SBUS input does not work at all. So I need some help to find out where the problem is. Please help?

Here is part of the RC input schematic:

image
image1019×536 15.3 KB

74LVC2G86DCUR chip inverse input signal when PD15 in HIGH, as its written in comment in table
Anyway, I have connected PD15 line directly to 3.3 voltage to be sure that its inverts signal.

I also checked the signals with an osciloscope:

SYS_USE_IO is 0
RC_INPUT_PROTO is SBUS

Here is what rc_input status shows:

nsh> rc_input status
INFO  [rc_input] Max update rate: 250 Hz
INFO  [rc_input] UART device: /dev/ttyS5
INFO  [rc_input] UART RX bytes: 224
INFO  [rc_input] RC state: searching for signal: SBUS
rc_input: cycle time: 28296 events, 179078us elapsed, 6.33us avg, min 4us max 1099us 17.836us rms
rc_input: publish interval: 0 events, 0.00us avg, min 0us max 0us 0.000us rms

And another one test, i have connect rc receiver to TELEM2 and switch RC_PORT_CONFIG to TELEM2 and it works fine. So I am shure that rc signal is received, it can be decoded. Also I have invert signal as its should be.

At the moment I have no idea what to check or change to fix it. Please help.

1 Like
2

Are you trying to connect it to USART6 Rx? Try with a Tx pin.

3

Yes its connected to, PC7 - USART6 RX.

Heh, in my case this pin is just not routed, I will try in next revision.
image

But why do you suggest this? Because USART will use the Tx pin if it set up as single wire?

4

Exactly, v6x has hardcoded singlewire in board_config.h. You can remove it and rebuild the firmware if you want to use it on the Rx pin.

2 Likes
5

Yes, everything works! Thank you! Just removed this line

6

Just keep in mind that when singlewire is not used telemetry is not possible.