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Need help with wireless idea


#1

Howdy.

a little background, I’m a .Net developer, and have done a fair bit of tinkering with the likes for fez panda, fez spider etc, but I am a novice when it comes to electronics.

Now, my idea
I want to be able to ‘search’ for an item (not using GPS if possible, to keep cost down).

The purpose of this is that it would be for an airsoft prop.

there would be many transmitters out in the field, and I would like to have a device that can ‘find’ them.(IE: it can tell you what direction its in - if your close enough)

the obvious answer is wireless with a directional antenna on the ‘searching’ device, using signal strength as your guide.
it would only need to be bi directional (IE: the ‘searching’ device doesn’t talk back)

I’m doing a very poor job at explaining this, so let me know if there are any points you want cleared up.

My question is this, is there something stupid I’m overlooking that would do the same/similar thing easier?

Thanks guys,
Regards
Mark


#2

Hi Mark,

interesting problem/idea. I suspect however that you should revert this to be more of an RF direction-finder problem than a microcontroller one. Here’s a random site I found that might give you some pointers… http://homingin.com/


#3

Mark,
It works great in a large anechoic chamber when the transmitter is using a perfectly-uniform dipole antennas and the “listener” is using a very high-quality directional antenna array (yes – array – you can’t really use single antennas, since they don’t have good enough directionality, so you combine multiple antennas together into an array, where you look at phase differences, usually with the help of adaptive DSP techniques).

It works well enough if you have very few antennas, and you’re using it for homing – in other words, you spin the antenna around, find the strongest signal, and start walking toward it as you keep spinning the antenna around. You will, eventually, reach the antenna.

But you can’t really use it in indoor environments. Of course, you can only have one tag chirping at a time – so you’ll need a way to cycle through the tags if you want to detect all of them.

It really just depends how well you need it to work.

As a PhD student who designs RSSI-based localization devices, I can tell you that it’s not an easy feat, and you’re going to have to become pretty familiar with antenna theory and electronics if you have any interest getting something going. There’s no off-the-shelf solution I’m aware of.


#4

Cheers guys,

Perhaps some GPS chips + xbee (or similar) is starting to look a lot more bang for buck.

Thanks,


#5

What kind of range do you need? Is it outside or inside? If it’s inside or outside at night then using IR could be a cheap option if it’s OK to only detect the objects once you get fairly close to them.

I’m thinking you are probably talking about a large field, though. So, GPS with pre-determined coordinates is probably going to be your best route.

However, an alternative to using a micro would be to use a smartphone. The LiveSight feature of Nokia HERE Maps for Windows Phone is an example of a really good implementation of what you could do.