Distance Measurements

Forum 2005-2010 (read only) General Frequently-Asked Questions
1

Hi!

How do I go for real-time distance measurement between two objects?

I thought of two methods, I'm not sure which one is more efficient

  1. Two 3-Axis Accelerometers communicating with XBEE (or something else), and I guess also 2 arduinos (unless there is some sort of stand-alone accelerometer with wireless capabilities, because one of them will only need to report the values wirelessly and nothing else).

  2. An Ultrasonic range finder and an arduino.

The second one is probably easier to do but the range is limited. From what I gather the maximum range is at around 6m (at least with reasonably priced sensors)

The first one, will require to start at a known distance (which is not really a problem) and then by figuring out the changes in position of the two sensors the new distance can be calculated. I am not sure about the accuracy of the measurements though, also I am worried that over time the accuracy will start getting worse and worse.

What I need is:

To measure the distance between two objects close to realtime within a range of 30m (ideally, 15m is workable as well) with precision of +-15% of the actual distance or less. Mounting things on both objects is fine, requiring line of sight is fine (but not preferable). Having to start at some known distance between the two things is fine.

2

Hm, in the Exhibition Forum is a 3D Laser Scanner, maybe this could be something for you?

3

I already looked at that and it has a range of something like 3m and I don't think it will do.

4

how big are these 'objects'? Could you mount 2 groups of ir leds on them and use a wiimote camera to detect them? Then measure the distance between them.
From my experience I think you'd need the 2 IR lights say 1m apart. Bit of a guess but gives you some idea to work with.

I wouldn't dismis ultrasonic too easily - the limiting factor with ultra sonic is the fact that you'r relying on the reflection of an object hitting the sensor ( a very small sensor! ),If you work out the fraction of the original signal that gets returned to the sensor you soon see why the range is limited.
if you could have a second slave device on the other object that would simply parrot the ping back you could significantly boost the range of ultrasonic. Kind of an active reflection rather than a passive one...