RSSI information available on 3DR radios

[JP B]

Hi all,

Putting this query here in addition to posting at DIYDrones 3DR spoecific forum, as I know some of you use 3DR products.  Hoping for a solution I will ensure any resolution is posted on both.

My question is - As I'm writing my own custom software on the APM 2.6 platform, using 3DR radios for two-way control and telemetry, I would love to display RSSI on my ground station user interface, but I dont know how to attain it.

Is the RSSI available at the "vehicle" end as attached to the APM and perhaps available via a pin read, or is RSSI available at Ground station end and perhaps available via AT/RT command?

Many thanks,

Jon-Paul.

[jesse brockmann]

Jon-Paul,

     FYI: the diyrovers group is not directly connected to DIYDRONES.  We are a separate group, however many of us use 3DR parts.  I have the 915mhz 3dr radios, and they have a RSSI command available in the firmware.   IT will sent out via serial port info about RSSI and packet data.  

3dr has full information on this available on their site.   http://copter.ardupilot.com/wiki/common-using-the-3dr-radio-for-telemetry-with-apm-and-px4/#Configuration_and_use_of_3DR_Telemetry_Radio

There is an AT for reporting RSSI.      First need to send +++ to put in command mode.  (Need 1 second before and after with nothing else)  That's a safety feature.    Then send AT&T=RSSI   (or RT&T=RSSI)    Use the ATO command to exit command mode.   You should now see output on the serial with link information.   FYI, I find it's a bit verbose, I wish there was a way to shorten the output.

Jesse

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[JP B]

Hi Jesse,

Thanks for the reply and highlighting the command mode and "guard time" as documented on your link.

1 second before and after - pah, that's not going to work for me being that my main use case is real-time control of rover by ground station pilot.  This makes me wonder how APM:Rover makes RSSI available both in manual and auto mode, I know when hooking up Xbee's you can assign RSSI to a pin then its a simple pin read.

Cheers,

JP.

[John Leichty]

From what I remember, the firmware running on those radios detects that both sides of the link are using MAVLink and injects packets with RSSI information. There's an option in the radio setup that enables this as well as MAVLink packet optimization, I think.

[jesse brockmann]

Jon-Paul,

 Once you have enabled the RSSI info command it will display it at a regular interval.   Therefore, the command to enter command mode only needs to be done once.     Not each time you need the RSSI information.

Jesse

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[Michael Shimniok]

Stupid question: what is RSSI?

Sent from my iPhone

On Nov 25, 2013, at 12:45 PM, JP B <jonpa...@gmail.com> wrote:

OK Jesse thanks, so it would be a one-time only case or at initial " mission startup" or switching RSSI on?  That seems straight-forward - taking onboard what John added, the standard software injects MAVlink RSSI packets, I wonder how they are getting the raw onboard data before they map that to a mavlink packet - I suspect one of the vehicle radio telemetry pins is accessible for this.

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[JP B]

OK Jesse thanks, so it would be a one-time only case or at initial " mission startup" or switching RSSI on?  That seems straight-forward - taking onboard what John added, the standard software injects MAVlink RSSI packets, I wonder how they are getting the raw onboard data before they map that to a mavlink packet - I suspect one of the vehicle radio telemetry pins is accessible for this.

Or methinks I am being thick and the radio firmware handles this independently of the APM......

[JP B]

http://en.wikipedia.org/wiki/Received_signal_strength_indication

I would like to know when signal strength starts to drop so I can "fence" my range limitations or turn around and come home.

[John Leichty]

The radio firmware knows the RSSI level independent of the APM (it measures it from the receiver circuitry). It also knows the remote radio RSSI level because the two radios pass it and other info back and forth independent of the user data in and out of the serial port.

The issue with obtaining the RSSI values with AT commands is you can't be passing data back and forth -- you have to drop into AT mode and then back out which takes a few seconds.

See MAVLink reporting here for more details on the RADIO packet injection. Unfortunately there isn't another good way to get RSSI info out without editing the firmware.

http://copter.ardupilot.com/wiki/common-using-the-3dr-radio-for-telemetry-with-apm-and-px4/#MAVLink_reporting

[JP B]

Thanks John, your explanation aligns with what I coming to understand after reading various info.

It would seem that after the 3DR mavlink option is switched on in the configuration tool, AND the radios receive mavlink heartbeats, RSSI info is injected into the data stream.

Currently I use my own custom message protocol.  I need to see what happens when I switch mavlink on - will my own custom messages still be shared successfully between rover and gcs, and if I inject mavlink heartbeat messages between rover and GCS will I then start to see mavlink RSSI info?

When next I have some free time, hopefully next week, I will give this a go.

Cheers again,

JP.

[Ted Meyers]

RSSI = Received Signal Strength Indicator

I ran into it working with XBee radios, but I was never able to get anything usable from it, possibly because there were multiple radios tranmitting in a noisy environment.

Ted