I think only inexpensive IR will work if you want the receiver to see the transmitter only if it pointed right at it. Microchip has very easy to use infrared IC chips that automatically modulate/demodulate UART messages to/from IR so you could use that to uniquely identify objects and know if you are pointed at the object. But you need line-of-sight.

An RFID tag will make a very simple transmitter, but if the transmitter is the passively-powered kind (not the actively-powered kind), your range will not be very far (but then you don't need batteries for the transmitter!). But it would transmit in all directions. Instead of knowing the direction the object is in, you would be able to tell when you are near it though. You could also have it beep faster as the signal got stronger so you could know how close you are to the transmitter.

What are you trying to do exactly? Search for items? Because then IR won't work all the time because you need line of sight. I would go with RFID to tell me how close I am to the object (rather than its direction) because that works just the same and because you dont need line of sight.

Its not that complicated it seems. Just a radio tag. You should be able to do it on your own...they just get to use custom boards and tiny components.

If you could find a way to use a YAGI antennae to detect an RFID tag signal (or you could make your own radio transmitter) then you would have directionality since the YAGI attenaes are very directional and very sensitive in that direction.

The idea behind this project is to transform the signal detected into a digital signal and then to represent it graphically on a x-y coordinate plan on a computer screen.
Eventually I could have the Z coordinate represented by the strength of the signal.
I think that with a device like the one I am talking about (but tell me, did you look the link?) if it would possible to estabilish a radial angle of sensitivity (that would represent the plain working area) then the emitter tag would be localized by the intensitivity of the signal.....
With an a/d converter should be relatively easy, with a certain degree of aproximation) to represent the situation on a computer.

Of course I would build either receiver and transmitter...
Yagy antenna? Unless it is possible to build a few centimeters yagy, I have already precised I am talking about a portable device.
Do a micro yagy would work? (I hope you know what you are talking about (with no offence, just I am not willing to waste my time and other's time)

Yeah, I looked at the link. That's why I was wondering if you needed to be able to detect the tag without line-of-sight, because if you do the nice super convenient IR method does not work.

The smallest Yagi's I have seen are pretty small, they are hand held but maybe a bit too big. They seem to be around 60cm which is probably a bit bigger than you want, but I haven't been really searching for antennas. I think I saw one that was 8" once. From what I can see the small Yagi antennae frequencies are much higher than a typical RFID tag which is good I guess since it would make for a smaller antennae. So if you go that route, you'd need to build your own RF transmitter.

Looks like this:
http://www.active-robots.com/product...antennae.shtml

I honestly don't know how they mapped out the angle and distance of the RF signal since power is affected by distance and by whatever is between the transmitter and receiver unless they somehow built a directional antennae into the handpiece. From reading the website it says that RF and RFID tags are used.

I understand what you are trying to say.

I'm sorry, I can't seem to find the 8" yagi antenna anymore (I do not even remember it clearly, 8" may have not have been the length of the antenna and another dimension).

If I were you, I would use regular RF to know if you were far or near and then use IR to tell what direction in case you have line-of-sight. Because IR is the best for narrow detection angle, except that it IR cannot travel through things. It would use RF to tell you if you are near or far, and it would use IR to tell you the direction (if it can see the IR). Maybe you can use a regular antennae and shield it on 3 sides so it could only receive signals from one direction?

Originally Posted by dknguyen

I understand what you are trying to say.

I'm sorry, I can't seem to find the 8" yagi antenna anymore (I do not even remember it clearly, 8" may have not have been the length of the antenna and another dimension).

The size of a yagi is dependent on the frequency of it's use, and it's length is dependent on you much gain and directivity you require. There are plenty of internet sites which will calculate you any type you need - but an 8" long one is going to be very high frequency.

Looking at the specs for 'loc8tor' it uses the 2.45GHz ISM band, so it will use pretty small aerials.

However, reading the website a little leads me to believe that elctrified doesn't understand how it works, and that it doesn't do what he thinks it does!. It doesn't give you a nice 2D plot of where an item is located, accurate to an inch or so - it's just a DF (direction finding system) and you follow it for maximum strength until you find the transmitter.

It's not a 'lot' of money, why not buy one and experiment?.

However, reading the website a little leads me to believe that elctrified doesn't understand how it works, and that it doesn't do what he thinks it does!.
It doesn't give you a nice 2D plot of where an item is located, accurate to an inch or so - it's just a DF (direction finding system) and you follow it for maximum strength until you find the transmitter.

I think I understand the purpose of this device.
I never said that it do plot, I said that this function must be implemetend in my own (that is the goal of my project)
If I could find any solution that allow me to have an external object to be detected and its position plotted on x-y axis I would go for that. If you know something about that please just let me know.
Even if you only have heard about it,or if you know how it could be called such a system I would know it, because at the present I don't even know what keyword to search for.

Any help for that is really appreciated .

It's not a 'lot' of money, why not buy one and experiment?.

well, as you have read on their site is not yet on the market.
Then I think that even buy one I am not shure I can understand the principle of working, even openin the box. The schematics would work for that.

. Maybe you can use a regular antennae and shield it on 3 sides so it could only receive signals from one direction?

Interesting thought, if you know it, can you tell me how to shield an antenna (just the principle) it would save me some time in searches for that.
I also thought to an antenna L shaped, or a microparabolic one,but I couldn't go more far than a thought.