### Author Topic: Measuring Distance between 2 Mobile Points  (Read 1672 times)

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#### arigid

• Jr. Member
• Posts: 22
##### Measuring Distance between 2 Mobile Points
« on: December 23, 2012, 08:33:13 AM »
Hi, I wanted help in determining between the distance between 2 points. It can be by either RF/Bluetooth or anything commercially available.
There were 2 cases i had considered, and it would be great if someone here could suggest something to use for both of them.
Case1: Both the objects are in the same room, and are in direct view of sight with no obstacles in between them.
In this case the distance and the direction of the other with respect t one is to be found.

Case2:
Both the objects may have obstacles like walls/chairs in between and distance & direction are to be measured, The distance may not be exact but slight variation would do.
Can someone suggest what kind of communication to use for this purpose.
Thank you for any help in advance.!

#### jwatte

• Supreme Robot
• Posts: 1,345
##### Re: Measuring Distance between 2 Mobile Points
« Reply #1 on: December 23, 2012, 10:49:40 AM »
Doing radio or light based distance is hard unless you use ready-made sensors, because of the timing and tolerances involved.

You could probably do a reasonable sonar-based distance determination. Ping at a known frequency, and then respond back with a pong at another known frequency when detecting it, and measure the time distance. Be sure to compensate for the detection/interrupt latency between signal arriving and actually being detected on each end (you can measure this empirically.)

#### Soeren

• Supreme Robot
• Posts: 4,672
##### Re: Measuring Distance between 2 Mobile Points
« Reply #2 on: December 24, 2012, 11:16:38 AM »
Hi,

I wanted help in determining between the distance between 2 points. It can be by either RF/Bluetooth or anything commercially available.
You can't do it by any kind of RF (BT is radio as well), as lots of ambient factors influence the propagation speed.

For line of sight, Bosch makes awsome LASER "tape measure" units. They're not exactly cheap, but very precise (like max. 5mm deviation in 40m)

With RF, you could however triangulate a single transmitter, using 3 receivers in a delta formation, some distance apart. You'd need to compare the phase of the received signals to find the "time difference" (to find the approximate angle and distance), but you'd need the distance between the receiving antennas to be a few percent less than a wavelength and while easy at high frequencies (which is harder to work with), using a sensible frequency like say 30MHz, they'd have to be almost 10m apart.

Cutting to the bone, it's a case of; if you have to ask, you probably don't have the experience it'll take to get a working solution. Measuring, comparing and storing phase timing is not for beginners.

The 30MHz signal quantized into just a rough measure of 100 possible steps, gives you 333ps/step, so takes super fast electronics to handle (no microcontroller can handle this) and even the PCB layout will have a huge influence, so you really have to know your way around it.

Case2:
Both the objects may have obstacles like walls/chairs in between and distance & direction are to be measured, The distance may not be exact but slight variation would do.
"slight variation"? (We work with numbers )

Except for triangulating an RF signal, nothing would work through a wall.
Regards,
SÃ¸ren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?