I would like to use RSSI to locate an object in a 3D space. The space will be a square box with transmitters located on the 4 corners. An object will be place at certain positions within the box and I want to be able to determine its location inside the box. Much like an internal GPS.
I would like to know what components (IC's?) I need to perform such a task.
Or if anyone else has any other more effective methods to acheive such a task your comments are welcomed.
since RSSI devices (most of them) can output analog for a project that you have in mind. a uC (microprocessor) would be suited for that. Look at the AVR line of programmable chips. You'll need a DEV starter kit and learn a little about programming. THey have chips that offer multiple ADC (Analog to Digital ) converters. With these chips, they have enough power for a HID (Human INterface device) or simply output some coded results to your computer via a serial port and write some software. You may also want to look at Rabbit core embedded processors. With those, the hassle has been taken out of making a board. etc.. look them up on line.
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"I'm never wrong, once i thought i was, but was mistaken"
Real Programmers Do things like this.
http://webpages.charter.net/jamie_5
RSSI will indicate only the received signal strength, not distance - and there are a lot of reasons why an accurate position indicator is impractical using only this method, especially in the near field of the TX antennas.
It certainly won't work for VHF and above. I have had some success with short range position indicators using 125 kHz sources. If that is feasible for you, please indicate the dimensions you are working with.
The project is to locate a r/c boat in a roughly 2 to 3m^2 water filled box, hence the transmitters or recievers will only be on the 3 or 4 walls of the box.
It will need to be fairly accurate considering the size of the box relative to the size of the boat (i.e down to cm's).
We are also considering placing a webcam above the box and using image processing to locate the boat, however I thought we might get more accurate results using RSSI.
I hope that helps.
Josh
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This detail would have been useful at the start! So is it a 2 dimentional problem or a 3 dimentional problem? i.e. can the water level vary? If it can vary then you can use a simple water level meter and then turn it into a 2 dimentional problem.
Nope, not a chance. Visual object recognition is the way to go, with a water level meter if needed.
Josh, he is wrong. It can be done (sort of) on a larger scale, but at the small scale you are talking about it's just not possible as other posters have mentioned. You would be lucky to determine if the object is inside the box or outside, let alone its position inside.
Seriously, start your backup plan now. Then it just becomes essentially a software project.
You are wasting your time, visual object recognition is the best method in this particular instance. All the other methods (RSSI, acoustic, and IR) require a transmitter on the boat and multiple receivers. Visual recognition on the other hand doesn't require any transmitter, will work with almost any size or type of object, is simple, fairly accurate, will most likely only require one receiver, and reduces the problem to essentially a software solution.
Thanks for everyones help, especially David Jones, I will be going with the visual recognition. It was originally my first choice though, as you do, I wanted to exhaust all possible options before finalising the decision as you never know there might of been an easier, more efficient way.
I've worked on someone else's image processing software that used a camcorder to track a lizard's frame to frame movement down a small track ~1.2M long or so.
You'll need to correct for parallax unless the camera is very high above the tank, so having a X,Y marks around the edges of the tank would help.
Python and Python Imaging Library was used to convert the colour image to greyscale first and then to two bit black and white if a pixel was either side of a set threshold value. This gave a black background with a white moving object on it that could be scanned vertically in my case to give the amount of movement in pixels which was then corrected for parallax and converted to millimetres.
Personally I think Phil is quite right to call you a stupid troll. It's not as if you are not fishing for ideas.
I'm even less amazed that one of your skills appears to be hunting down information about someone who has the gall to call you stupid.....
Strange that.
Did you use Google to find out Phil is occasionally slightly obnoxious rather than reading this 'newsgroup' for a while?
Uuuuuhmmmmmmmmm............
Anyway.
Since I am brilliant, capable of thinking outside the box and it sounds like a 'fun' way of solving your problem. What you should really do is this....
Think in polar coordinates.
Pick one of the 'vertices' of your box as your 'origin'. Get yourself three 'dual light pipe' type things and lay them out along the XYZ edges of your box as defined by that origin.
Plug the mechanical ends of your light pipes into some mechanical type rotating scheme, stepper motors with microstepping drive systems, so you can rotate them.
You will probably need some blu-tac to stop the water dribbling out.
Excellent opportunity for mechanical design of things that overcome dribble problems.
Then you shine a bit of light up one side of your dual light pipe thing and you recieve the reflected light back down the other side of it.
Lots of opportunity for transmission/modulation/detection/demodulation stuff there.
And rotate the pipes for maximum signal.
Lots of opportunity for feedback/control stuff there.
Once you have aligned all your pipes. Then all you have to do is do sums to convert the angles to where your object is.
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