multiple sonar sensors

[leeguy92]

hi, all.
I need to build two robots, which will each make use of sonar ranging sensors.
I have never done any serious robotics before, but it seems to me there could be a problem(a large one) here where one robot hears another's pulse and assumes it to be it's own.

what are my options here? can i operate one robot at a different frequency, so it isn't heard by the other one?
It just seems like they are all 40khz.

Any help would be appreciated.
Lee.

[szhang]

yeah they'll get confused.  For one robot usually what you do is fire the sonars in a some order, like firing the ones in the front, then ones in the back etc.  you have to play with the order to get it working right.

For two robot, it is really hard unless there are walls between the robots.  You can play with the frequency if you have just a tranducer and make your own circuit to process the signals.  But I don't know how well that'll work.

[leeguy92]

thanks for the reply.
The actual application is two robot 'tanks' in a circular arena, which each have an infrared beacon on top of them.
The sensors on each robot allow it to tell if it is looking at another robot(infrared photodiode), and how far away it is from objects such as walls, and other robots(Sonar).
so separating them isn't really an option.

The only solution i can think of is to somehow allow one robot to take control, so that only one robot can fire it's sonar at a time, and they would stay synchronized. i think a wireless system is just overkill.

hmm.....

[leeguy92]

ok, i just had an idea.

Is it possible to get infrared LED/detector pairs which operate on different wavelengths?

I would prefer to leave sonar out of the equation anyway because of echo complications.

[Admin]

The only solution i can think of is to somehow allow one robot to take control, so that only one robot can fire it's sonar at a time, and they would stay synchronized. i think a wireless system is just overkill.

Having them communicate to take turns using sonar is the best option. I've done it and it works well.

Is it possible to get infrared LED/detector pairs which operate on different wavelengths?

but . . . infrared is a specific wavelength already
browse through the IR sensor datasheets and look at their sensitivity vs wavelength charts . . . you might find two that are different enough to work

[leeguy92]

thanks for the reply.
so, what communication method would you use?
any particular protocol - bluetooth?
if not, what frequency is good (and legal in the uk) for this(i would imagine 27mhz)

it really needs to be a module - i have no experience(though, lots of reading) of building wireless circuits.

[Admin]

I used a wireless internet connection (the robots all had laptops).

Any wireless module you buy will work and should be legal (or they wouldn't sell it).