Homing Device

Hi,
Ive just started to work on a project as part of my bachelor's degree, and i was wondering if its possible to build from Arduino a homing device that can detect an object's direction from the receiver, relative to it.

The distance it has to detect the transmitter is about 30-15 meters (about 98-49 ft), no more than 30 but no less then 15.

From the little search i did, so far i didn't find anything definitive except something called Xbee, a receiver that can detect distance, not sure if it can actually give an indication of it by units or just signal strength and if it can show the direction from where the signal is coming from.

Arduino is totally new to me, so go easy on me 8).

P.S

It doesn't have to be RF based, it can be anything that can do the job of homing on a specific target.

What sort of terrain will this be over?
Flat level floor, car park, grassed sports field, ploughed field or rough ground?
Will it be level enough for 'line of sight' detection from the top of the buggy at all times?
Will there be obstacles that have to be avoided?
How big will the 'target' be.
Will the 'target' be flat on the ground or vertical, and if vertical, how high off the ground will it be?
These are just some of the details you've omitted. I'm sure others here can think of more.
Please explain, in as much detail as you can, the problems you need to overcome.

If using radio, you will need a receiver with a directional antenna and signal strength readout. While that will allow you to determine direction, it is difficult to impossible to estimate distance from signal strength.

What accuracy is required. centimeters, millimeters.
I am thinking ultrasound transmitter on the object and three receivers in a triangle around it.
Position/movement can be calculated from the arrival time of the transmitter's (pulse) signal.
Leo..

Basically its a small device, 300x300x300 mm in size, that can locate a person floating on a calm water surface, go to him avoiding other people (a minimal amount), and return to a docking station on a fixed spot.

Henry_Best:
What sort of terrain will this be over?
Flat level floor, car park, grassed sports field, ploughed field or rough ground?
Will it be level enough for 'line of sight' detection from the top of the buggy at all times?
Will there be obstacles that have to be avoided?
How big will the 'target' be.
Will the 'target' be flat on the ground or vertical, and if vertical, how high off the ground will it be?
These are just some of the details you've omitted. I'm sure others here can think of more.
Please explain, in as much detail as you can, the problems you need to overcome.

-Terrain: flat and calm body of water with little or no ripples.

-Line of sight: as i said it should operate on top of water so it'll have to avoid other people but i know that Arduino has proximity sensors (IR, US) with which i can avoid obstacles, correct me if im wrong. But in general there is almost always line of sight.

-Obstacles: other people but scarce.

-Size of target: a human profile, the same way someone flots on a Inflatable mattress in a pool.

-Target elevation: same level as the device.

-Distance from target: 30-15 meters from the docking station of the device.

jremington:
If using radio, you will need a receiver with a directional antenna and signal strength readout. While that will allow you to determine direction, it is difficult to impossible to estimate distance from signal strength.

If the directional antenna is compact enough in size and wight (for the max distance of 30 meters in need it to detect) and i there is such a thing for Arduino that it can work with, i think it'll be perfect. The distance output is negligible if i can actualy make something that can track a targets location. As i said at the beginning of the thread Xbee i think i can work with it for judging the target/docking station distance.

Wawa:
What accuracy is required. centimeters, millimeters.
I am thinking ultrasound transmitter on the object and three receivers in a triangle around it.
Position/movement can be calculated from the arrival time of the transmitter's (pulse) signal.
Leo..

I need it to be able to get in a range of about 30 cm from the target.

How should this device identify the target person.
Facial recognition?
Body profile (boobs)?
I visualise this thing as a robotic waiter, bringing a drink to a certain person floating in a tropical pool.
Leo..

Xbee i think i can work with it for judging the target/docking station distance.

No, you can't.

If anyone claims otherwise, ask for the complete details on how it is done, and do let us know. That question is asked on this forum about once every three days, and no one has yet reported success.

Have you thought about how your locator will avoid other persons?

Wawa:
How should this device identify the target person.

Body profile (boobs)?

count me in, i invision, like baywatch, is this a lifegard stand?

Wawa:
How should this device identify the target person.
Facial recognition?
Body profile (boobs)?
I visualise this thing as a robotic waiter, bringing a drink to a certain person floating in a tropical pool.
Leo..

well by now i dont really care how it will recognize the target color, sound, RF, boobs or any other shape for that matter as long as it can juts point the direction, and yes the waiter thing is one of the potential applications.

jremington:
No, you can't.

If anyone claims otherwise, ask for the complete details on how it is done, and do let us know. That question is asked on this forum about once every three days, and no one has yet reported success.

Have you thought about how your locator will avoid other persons?

i just saw a youtube video of a guy that built a device use series of light LEDs that light up or turn off depending on the signal strength/distance from the transmitter.

Ive got some general ideas of avoiding depending on the type of receiver but in general it can avoid by proximity detection using US or IR sensor. As i see it now this is the least of my problems, i really need to figure the direction lock problem.

Google "bee tracking device" (the real bees).
A small (passive) antenna glued to the animal interferes with a transmitted signal from the "Homer".
High tech high frequency radar stuff though.
Leo..

My original idea was to use a couple of coloured panels that suitably filtered photo-transistors could detect from a distance, but the ‘other human bodies’ and the wave motion of the water would prevent that from working, as they would for any optical system.

As you need the device to be on water, have you thought about Sonar detection? A ping from the device initiates a different frequency ping from the target. As the two get nearer to each other the return ping will be heard sooner. Also, Sonar detection can be made directional.
That may not get you to the target by the most direct route, but it will get you there eventually.

Infrared.

Imagine holding down a button on your TV remote. Then the robot has two or more IR sensors which receive this signal. It rotates until the signal is lighting the 'front' detector and paddles in that direction. The transmitter will have LEDs pointing all directions so it doesn't need to be pointed at the robot.

Avoiding people in the water will be difficult. Most sensors can't tell the difference between a person and a wave. Perhaps bump detectors, like a Roomba robot?

MorganS:
Infrared.

Imagine holding down a button on your TV remote. Then the robot has two or more IR sensors which receive this signal. It rotates until the signal is lighting the ‘front’ detector and paddles in that direction. The transmitter will have LEDs pointing all directions so it doesn’t need to be pointed at the robot.

Avoiding people in the water will be difficult. Most sensors can’t tell the difference between a person and a wave. Perhaps bump detectors, like a Roomba robot?

What if people are between the IR transmitter and receiver?
Ever tried changing the channel on your TV if someone is in the way?
Hence my comment about optical systems not working.

Well after some more research and google digging i foud that a lot of RC plane pilots build their own tracker using RSSI tracking method, like this guy, this exactly what i need judging from the post and video, and i can make it compact because i dont need the second antenna.
The problem now is that i dont know what parts i need, the coding part i think i can manage by myself.

The problem now is that i dont know what parts i need, the coding part i think i can manage by myself.

Start out with the same parts as your RC pilot guy uses, and develop from there.

You will (re)discover that reflection and absorption of radio waves by nearby objects and the relative orientation of transmitting and receiving antennas have dramatic effects on the RSSI; far larger effects than the distance between the transmitter and receiver.

To visualize these effects on the signal from a WiFi router within an apartment, an app has been developed for Android phones. Take a look at this blog, describing the results.

But by all means, get a couple of XBees and try it out yourself. It will be an interesting educational experience.

You could try two 2.4Ghz vertical aerials (as on a Wifi modem), spaced 1.5wavelength apart (187.5mm).
BOTH connected to the input of ONE 2.4Ghz receiver, with EQUAL LENGTS of (x wavelength) coax*.
*signal in coax does not travel at lightspeed.
The AGC/signal strength output of the receiver will indicate max signal if the aerials are 90 degrees to the transmitter source, because the signals of the two aerials are in phase.
And, more important, the signal will NULL if the aerials are INLINE with the source.

A second set of aerials and a second receiver can be used, so you don't have to "scan".
e.g. four aerials mounted in a square. One set in oposite corners.
Leo..

jremington:
You will (re)discover that reflection and absorption of radio waves by nearby objects and the relative orientation of transmitting and receiving antennas have dramatic effects on the RSSI; far larger effects than the distance between the transmitter and receiver.

To visualize these effects on the signal from a WiFi router within an apartment, an app has been developed for Android phones. Take a look at this blog, describing the results.

But by all means, get a couple of XBees and try it out yourself. It will be an interesting educational experience.

Tnx for the blog article, i enjoyed reading it but i don't think that this should concern me, yet. The final test of the project will be in so called "lab conditions", the body of water that the robot will operate on has a year-round calm water surface and the plane of operation will be free from obstacles, so the receiver will have a clear line of sight to the transmitter. But this is just the first stage of the project (about 2.5 months until presentation) where i'll try to demonstrate the basic concept of work.

But as i said tnx a lot for the info, and i'll keep it mined for further use.

By the way im not really sure for what the Xbee are used for, and what can i do with them to elp me with my project?

Wawa:
You could try two 2.4Ghz vertical aerials (as on a Wifi modem), spaced 1.5wavelength apart (187.5mm).
BOTH connected to the input of ONE 2.4Ghz receiver, with EQUAL LENGTS of (x wavelength) coax*.
*signal in coax does not travel at lightspeed.
The AGC/signal strength output of the receiver will indicate max signal if the aerials are 90 degrees to the transmitter source, because the signals of the two aerials are in phase.
And, more important, the signal will NULL if the aerials are INLINE with the source.

A second set of aerials and a second receiver can be used, so you don't have to "scan".
e.g. four aerials mounted in a square. One set in oposite corners.
Leo..

From what you've written here, i'm guessing that you know a thing or two in RF communication, so if you don't mind i have some questions.

-If i use 2 of the antennas, i have to mount them upright so they'll create a vertical plane, right?

-If i use 2 antennas i'll have to mount them on a 180 degree panning platform so that they can scan, or can they be stationary and the robot will steer itself to a position that the signal will be the strongest?

-If i use 4 antennas, do they have to be mounted horizontally or vertically?

-If i understand it right, if the signal will NULL it means that i lost the signal completely from the robots point of view, and it'll have to correct its heading ti find it again?

-How can i create the signal for the robot to lock on, and can i configure a specific wavelength for the robot to lock on?

I would start experimenting with two vertical antennas mounted on a horizontal metal plate, about 1.5 wavelength apart.
Have a hole for one aerial, and a slot for the other, so you can adjust/finetune the distance between the aerials.
As said, connect to a receiver with fieldstrength/metering output with EQUAL lengths of coax.
There are less misalignment/reflections in the coax if you cut that at wavelengths.
The coax used might have a propagation delay of 0.66-0.85.
Your transmitter has to send an almost continious signal, or identification code.
I expect you will find a sharp dip when the aerials are inline with the transmitter.
And a broad maximum when the aerials are 90 degrees to the transmitter.
What you do with that is up to you.
Leo..