Radio Signal Intensity

[marco.tognon]

Hi!!

Does someone know a way to read the intensity of the Radio signal from the dongle??? I was thinking that it could be a good sensor of distance.

Marco

[tobias]

That is a little drawback with the nRF24L01+, there is no RSSI to get a signal strength measurement from. It is possible to use the packet retries as a rough measurement though but as there are so many things that effect the packet retries I don't know how well it would really work.

The crazyradio.py contains the send_packet function which returns number of retries (retransmits). It is then used in the CRTP layer in radioediver.py as a callback link_quality_callback. The Crazyflie class takes care of that callback with _link_quality_cb and is finally used in the GUI.

[marco.tognon]

it is a realy pity!! I think that the number of retries is quite different for the intensity of the signal

So i cant use it for my purpose. Do you know if there could be another way to estimate the distance of the crazy flie from the dongle?

[hsanjuan]

Wondering, what is "your purpose" in the first place?

[marco.tognon]

I read that the nRF24L01+ has a Received Power Detector measurements that is only a 1bit

from the datasheet: Received Power Detector (RPD), located in register 09, bit 0, triggers at received power levels above -64
dBm that are present in the RF channel you receive on. If the received power is less than -64 dBm,
RDP = 0.

.
But i think that is not enough for measure the distance!

But has the crazyflie the same tool or is different?? My ambition is have two crazyflies that can comunicate each other and measure their relative distance.

[tobias]

I think you could get a rough estimate by transmitting(pinging) with different power settings and test when you get something back.

Code: Select all

SPI RF-SETUP(RF_PWR)           RF output power         DC current consumption
11                               0dBm                    11.3mA
10                               -6dBm                   9.0mA
01                               -12dBm                  7.5mA
00                               -18dBm                  7.0mA

[marco.tognon]

Do you mean calculating the time between the trasmission and the reception?? but with this implementation both the device must know the start time of trasmission! it could be a problem!!!

But is possible to have two crazyflie that comunicate each other? Or what kind of sensors can I mount to estimate the distance of a crazyflie from another?

I was thinking to use a camera, but the various implementations use a trasmitter i think it can't trasmit on various channel!!!

The best could be somthing on board but since low payload and little computationa capacity i cant find an adequate sensor!!!!!

[tobias]

I think you need to be a bit more specific about you requirements. How precise do you need to know the distance, do you need to know the direction etc.

[marco.tognon]

The project is just started so the goals are not so clear For now I'm trying to understand what i can do and what i can't do.
For now the main idea is to have about 10 crazy flie which have to cooperate together!! One easy algorithm to have a stable swarm is to keep constant the relative distance form every robots. But for this, any robots have to know the distance from its neighbors.

Now I hope my goals are a little bit clearer.
Marco

[tobias]

That is also one of our dream goals but without advanced position tracking systems such as VICON it is very difficult to accomplice. I'm not yet aware of any research lab that has managed to do it without an external position tracking system. We have used a kinect to do external position tracking and with that it might be possible to control a couple of Crazyflies but I don't think that was your goal or?