I'm working on my senior project for college and In my design it would help if I had the distance between two circuits. The average distance is 2-8feet. I have looked at ultrasonic devices however it looks like they might need to be pointing at an object.. Does anyone have any suggestions. Power should not be a problem. And I can get them to talk to each other wirelessly... So THX ahead of time.

 

With a distance that short, I don't think you'll be able to measure it using any lightspeed-propagating signal unless you spend a LOT of money. Sound propagation gets you in the range of delays that you can measure with the tools available to mere mortals.

I'd try getting the modules synchronized as best you can using wireless, then have one emit a chirp (ultrasonic or audible) and have the other one listen for it. Do this a few times and I bet you can get a reasonable range estimate.

 

Great thanks for the advice! I will attempt that in the meanwhile anyone have an idea as far as directionality on this other circuit that is x-feet away... like a compass that points to the other circuit?

 

The simplest way may be to use two (or more) ultrasonic transducers on the moving end of the link, angled slightly apart so you can compare the relative signal strengths.

Another possiblity is to use a focussed or slit-masked IR beam with the receiver mounted on a model servo so you scan around to locate the transmitter angle.

You could possibly use the same idea with a single ultrasonic transducer and continuously adjust the angle to track the strongest signal.

 

Do you need to determine direction or just distance? John

 

@jpanhalt; I will need the direction and distance.

@rjenkins;
Not sure on comparing relative signal strengths, however I was thinking about a 20-25 ir light on circuit1 and on circuit 2 we have a 4 way array to locate the ir light to provide directionality.

The next step is to include a compass on each circuit so that circuit 2 will have the distance, relative angle, and current heading of circuit 1. With that information I should be able to extrapolate a predicted collision path.
Thx for comments... all are welcome!

 

The way that it is done with bigger units, is to use a constantly rotating arm, with two microphones one on each end. The doppler effect in the microphones (the amount that the frequency is off from the other only, doubles the effect) gives which side the noise came from. Then the difference in time hitting the two phones gives the triangulation point (otherwise you require 3 microphones minimum).
I have seen a few compass units on ebay relatively cheaply (am I allowed to say sureelectronics, I have bought several items from them, and only ever had a problem with a digital oscilloscope that was DOA. Had no rapid response from them so had to use paypal to refund the money. Apart from that, I am intending on purchasing some more smaller items from them, some wireless tranceivers). Add in an accurate accelerometer to the units, and they could also work out their relative positions.