problem with externally powered RFD900 on Pixhawk

[Andrew Tridgell]

Hi Seppo,

I found an issue with the RFD900 on Pixhawk when the RFD900 is
externally powered.

The bootloader of both the RFD900 and 3DRRadio is setup to stay in
bootloader mode on power on if the CTS pin is held to ground. This is a
failsafe way of ensuring we can flash new firmware if the firmware
becomes corrupt.

Until recently most people would have connected only the GND/RX/TX/VCC
lines to the RFD900 so CTS was never held low. Now that we support
RTS/CTS in Pixhawk it is more common to connect all 6
pins. Unfortunately if the Pixhawk is externally powered then this means
the RFD900 will get stuck in bootloader mode if CTS is connected to the
Pixhawk CTS pin.

This doesn't happen for the 3DR radio or for the RFD900 if powered off
the Pixhawk UART as the power pins of those ports are only switched on
after the UARTs are configured. This means that the pin is held high
when the radio is powered on.

When the Pixhawk is externally powered the CTS pin is held low when the
system is powered on. Philip has a look at this and thinks it may be due
to the way the buffer chip on page 2 of the Pixhawk 2.4 schematic is
used.

I think the simplest solution is to change the SiK firmware for RFD900
to accept the pin next to RTS (pin 7) as CTS, perhaps by setting
RTSCTS=2 in the parameters? Or perhaps by default?

Alternatively we could change the RFD900 bootloader to use a different
"stay in bootloader" pin, but we then need to offer a way for users to
update their bootloader (which is not trivial at the moment).

Thoughts?

Cheers, Tridge

[Gary McCray]

Hi Tridge,

Slightly off topic, but I noticed that although the RFD900 was an existing (last edited in from Google by me last June) wiki page it was not installed in the Instructions or TOC menus.

I have corrected that.

But it seems to me this page might want some up dating and I also saw some information regarding set up for the RFD900 on an old blog here:

http://diydrones.com/profiles/blogs/9xtend-vs-rfd900-radio-high-altitude-test

But it does not appear integrated with the wiki.

It seems to me that the wiki needs a seriously upgraded what it is and how to use it page.

Happy to work on this if you could provide me with basic direction.

Best Regards,

Gary

[Andrew Ferrara]

Yes, please update the RFD900 page for use with the Pixhawk. I'm currently trying to set it up myself and running it to some questions that could easily be answered in the documentation.

How would one go about setting up the RFD900 for the pixhawk? Do you need all six pins or just Rx Tx 5v and Gnd?

Pixhawk Telemetry Pins (left to right)
5v Rx Tx CTS RTS GND

Thank you,

Andrew

[Andrew Tridgell]

Hi Seppo and Kevin,

I just found out today that the issue I reported isn't specific to the
RFD900, it can also happen on the 3DR radio, but in a different way.

If you have two 3DR radios connected, one to a laptop and one to a
Pixhawk and you remotely change a parameter on the air radio using
either MissionPlanner or the CLI, and then remotely reboot the air radio
(with RTZ for example), there is a good chance the air radio won't
reboot, and will instead get stuck in bootloader mode. This happens if
CTS happens to be held low at the time of the reboot.

Given that the CTS pin is normally controlled by the radio, it may be
sufficient to just do SERIAL_CTS=true when we reboot the radio
remotely. Worth a try anyway.

Cheers, Tridge

[Jonathan Challinger]

Any way to get around this? Plug in RFD900 after PIXHAWK is powered on?

Can the UART supply enough power for the RFD900 at 30 dBm? Is the concern just noise or is it amp draw? I don't think I really want to have a separate (third) BEC in the plane unless I absolutely have to. Currently the ESC is powering the servos and the output rail, and I used a CC BEC in my power module.

Cheers, Tridge

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[Andrew Tridgell]

Hi Jon,

> Any way to get around this? Plug in RFD900 after PIXHAWK is powered on?

yes, that works, but it isn't convenient.

> Can the UART supply enough power for the RFD900 at 30 dBm? Is the concern
> just noise or is it amp draw? I don't think I really want to have a
> separate (third) BEC in the plane unless I absolutely have to. Currently
> the ESC is powering the servos and the output rail, and I used a CC BEC in
> my power module.

I run my RFD900 at 27dBm, to account of the antenna gain and keep it
below the Australian EIRP limit of 30dBm. You can run it off telem1 on
the Pixhawk, but it causes about 0.1V noise on the 5V rail. That isn't a
lot, but I prefer to avoid it, so I usually power my Pixhawk off the
servo rail. I have a 20A BEC (a CC BEC Pro) on the servo rail, so it has
plenty of spare current. I have a petrol engine, so no concern about ESC
draw.

For now I've gone back to powering my RFD900 off telem1. I'll think
about a better fix. Probably the easiest is a new bootloader with a 10s
timeout, but it is a bit of a pain putting a new bootloader on.

Cheers, Tridge

[Karthik A]

Hi Andrew,

I am planning to do long range flights with my UAV, its a petrol engine with pixhawk as the Autopilot. I want to use a separate lipo battery for my pixhawk and connect a BEC circuit for my servo rail and my telemetry (RFD900) and a separate battery for my engine.

[Karthik A]

Any suggestions on this setup guys? Also the Antennae's that come with the bundle is efficient for what range?

[איתי גיא‎]

Is there a solution for powering rfd900 from external power?

is it still an issue? I am running it with SIK 1.9

[Jaime Machuca]

If you remove the jumper between pins 4 and 6, you can supply power via pins 2 (GND) and 4 (+5V).

Best regards,

Jaime Machuca Mercado

CTO | Droidika | www.Droidika.com

Mail. Ja...@Droidika.com

Tel. +52 (33) 3777 5327

Cel. +52 1 (33) 3945 3350

Este correo electrónico y cualquier archivo transmitido en él, son confidenciales y para uso exclusivo de los individuos y entidades a quienes está dirigido. Si usted no es el destinatario previsto o la persona encargada de recibirlo, y tiene por error este mensaje, queda prohibido y sin validez el uso, difusión, re-envío, reimpresión o copia. Toda oferta y/o aceptación de propuestas comerciales, celebración de contratos u otros actos tendientes a la adquisición de bienes o servicios, así como el establecimiento de cualquier clase de obligación legal para Droidika S.A. de C.V., deberá confirmarse por escrito firmado autógrafamente por funcionario competente, excepto que se cuente con un contrato vigente que autorice el uso de este medio para tales fines. Si usted recibió este correo por equivocación, favor de notificar inmediatamente por este medio a su remitente, y después borrarlo de su correo

[איתי גיא‎]

what does it mean?

what difference does it make?

[איתי גיא‎]

I meant ,

is their a solution for the CTS when powering the RFD900 externally ?

Itay 

On Saturday, March 15, 2014 at 11:36:54 PM UTC+2, Andrew Tridgell wrote:

[Jaime Machuca]

The RFD900 may under certain conditions require more power than the telemetry port on the Pixhawk can deliver, that is the reason why it is more desirable to power it externally. I am not sure, maybe someone on the HW side can confirm this, but if you pull more power from the Pixhawk than you are supposed to, you risk having a brownout.

Regarding the jumper, when the jumper is in place it allow the RFD900 to be powered through the FTDI input. when you remove the jumper it will no longer be powered from the FTDI so you must supply power through the 2 and 4 pins.

Best regards,

Jaime Machuca Mercado

CTO | Droidika | www.Droidika.com

Mail. Ja...@Droidika.com

Tel. +52 (33) 3777 5327

Cel. +52 1 (33) 3945 3350

Este correo electrónico y cualquier archivo transmitido en él, son confidenciales y para uso exclusivo de los individuos y entidades a quienes está dirigido. Si usted no es el destinatario previsto o la persona encargada de recibirlo, y tiene por error este mensaje, queda prohibido y sin validez el uso, difusión, re-envío, reimpresión o copia. Toda oferta y/o aceptación de propuestas comerciales, celebración de contratos u otros actos tendientes a la adquisición de bienes o servicios, así como el establecimiento de cualquier clase de obligación legal para Droidika S.A. de C.V., deberá confirmarse por escrito firmado autógrafamente por funcionario competente, excepto que se cuente con un contrato vigente que autorice el uso de este medio para tales fines. Si usted recibió este correo por equivocación, favor de notificar inmediatamente por este medio a su remitente, y después borrarlo de su correo

[Nate Weibley]

We were able to work around this problem by using a 1k pull up resistor between VCC and the CTS pin.