# Need Guidance for finding exact dist b/w 2 objects under 1 meter range

Hii Arduino lovers :),
This one is my third post on this Forum so expecting the same help just like i got on those two ;).

I have an idea in my mind which needs the exact distance between the two objects(may be a transmitter receiver pair) to be calculated. One of them is fixed at its respective location and the second one is mobile.They both are not necessarily should be in line of sight. The thing over here is that whole setup should come under a range of 1m2(even this is large).
Is this possible…?

I have tried searching on google and found using ultrasonic sensors or radio waves for this but i don’t know if they are suitable for smaller distances… :~… Still i have not ended up searching… 8)
I am ready to use more than one receiver as Triangulation to increase the accuracy of the system …

Any suggestions…???

Using ultrasonic sensors when the objects are not in sight is not going to work.

How "exact" is exact? Measuring distances based on radio signal strength is not going to give you anything like an exact distance. Plus or minus a couple of miles, maybe. Plus or minus a meter? Not a chance. And anything less than that is out of the question.

@PaulS: What would u say if objects are in line of sight........?? Is there any other way out....??

Aman24:
I have an idea in my mind which needs the exact distance between the two objects(may be a transmitter receiver pair) to be calculated.
One of them is fixed at its respective location and the second one is mobile.They both are not necessarily should be in line of sight. The thing over here is that whole setup should come under a range of 1m2(even this is large).

I don’t understand what the 1m2 refers to. Are you trying to measure distance to a resolution of 1m, or within a range of 1m (to what resolution?

Are you actually trying to find the relative position of the moving object, rather than the distance to it? Over what sort of range, and in what environment, and to what resolution?

Exact??? No such thing in the real world.

Exact to 2mm might happen with ultrasonic under controlled conditions. Shortest ultrasonic distance at Arduino speed is close to 2 cm. But big deal if you can set the sensor back that far from ‘point zero’ and math any effects from 2D displacement away. If you always go straight line then it’s a breeze.
Ultrasonic will change with air temperature, but very slightly per degree C. That can be calibrated out or a temperature sensor be used.

Possibly you could calibrate on received light to a sensor. That will vary with unsteady power and led aging and I dunno what else.

What moves the second point? Can you measure that? An X-Y table or arm gives many options.

I like the idea of using a light sensor if you'll always be in Line of Sight. What I would think is an LED positioned on object 1, and a sensor a fixed (known) distance from the LED. If object 1 were a circle of radius 10cm for example, put the LED at the center, and a detector at the edge of the object. You can use the value read at a fixed distance to calculate the total light output from the LED and then using the value measured with a detector on object 2, you could work out the distance.

The detector on object 1 is used to correct for LED aging or any other effects that might influence your measurements. The only problem with this would be that the detectors would always have to stay in the same orientation to the light source so as to provide the same detection cross section (can you get detectors that this wouldn't impact? Probably)

Are you actually trying to find the relative position of the moving object, rather than the distance to it? Over what sort of range, and in what environment, and to what resolution?

Well, i need to calculate the distance between the fixed and mobile object (relative distance would also do) within a area of 1 meter2. A resolution upto 0.8cm will do my job…

What moves the second point? Can you measure that? An X-Y table or arm gives many options.

NO…!!! the mobile object could be placed anywhere under the mentioned area…

@JoshWimble:

The only problem with this would be that the detectors would always have to stay in the same orientation to the light source so as to provide the same detection cross section (can you get detectors that this wouldn’t impact? Probably)

I don’t think this would help as the reading at the sensor side would greatly vary depending upon the orientation at which the mobile object is placed…

@PeterH: @GoForSmoke: @JoshWimble: Basically what i want to actually achieve is as follows: Consider a rectangular white page of say 1m x 1m. Now let us fix the sensors(whichever would be more appropriate) at the corners of this page(I am ready to use more no. of sensors to increase the precision and accuracy). let us assign coordinates as (0,0)(1,0)(0,1)(1,1) to this sensors. Now the the object can be both a simple like a pen or can be some sort of transmitter or led inbuilt to it or whatever(depending upon the method used) . So here i need to calculate the relative distance of that pen wrt say (0,0)...

Any suggestions....???

These sort of schemes don't work on the strength of the light. They measure the time it takes for either the ultrasound or the light wave or the radar wave to go there and back. As you get to shorter distances, the time becomes to short to measure without special equipment.

The other thing you can do, is have two lights on one device. Take a photo with a video camera on the other device and measure the distance between the two lights in the picture, you can calculate the distance that way. The further away the other device is, the closer together the two lights will look, in the picture.

Get a motorised car antenna. Get one device to poke the other device with the car antenna. Measure the time the antenna motor runs for.

Consider a rectangular white page of say 1m x 1m. Now let us fix the sensors(whichever would be more appropriate) at the corners of this page(I am ready to use more no. of sensors to increase the precision and accuracy). let us assign coordinates as (0,0)(1,0)(0,1)(1,1) to this sensors. Now the the object can be both a simple like a pen or can be some sort of transmitter or led inbuilt to it or whatever(depending upon the method used) . So here i need to calculate the relative distance of that pen wrt say (0,0)...

Any suggestions....???

Well when you put it that way.... put a webcam on the ceiling point straight down, analyse the photo.

michinyon: Well when you put it that way.... put a webcam on the ceiling point straight down, analyse the photo.

^^^ That.