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### Topic: Distance between two ( or more ) moving arduinos (Read 994 times)previous topic - next topic

#### fgalastri

##### Oct 05, 2013, 02:49 am
Hi all,

I'm new to this and I'm trying to find out if my idea is feasible. I found similar ideas but not quite the same, so I'd appreciate if you guys can help me with this one.

I need to know when two objects have a specific distance between each other ( 5, 10 or 15 meters ). I need to know when they are within this range and when they are not anymore. Those two objects will be moving at a reasonable speed ( between 20km/h and 50km/h ) and there will be no obstacles between them. The object in the front doesn't need to know about the object in the back, but the object in the back must know about the object in the front and if they are side by side. Something similar to a car race when the car in the back is going to overtake the car in the front. I need to know when the car in the back is within the desired range and when the overtaking is finished.

I read about lasers, sonic sensors, gps, RF, etc but so far no idea if this is feasible or not and if it is what is the best solution.

Thanks.

#### PeterH

#1
##### Oct 05, 2013, 02:56 am
There are people who've got that sort of thing working by doing video analysis and moving object recognition and tracking, but it needs a fair amount of work to develop and q lot of processing power to execute it. That approach is definitely not an Arduino project. I don't think an ultrasonic sensor is going to be feasible in the environment you describe, and I can't see any other way to achieve it.
I only provide help via the forum - please do not contact me for private consultancy.

#### mrburnette

#2
##### Oct 05, 2013, 05:32 am
Quote
50km/h

50K/(60*60) = 139 Meters/Sec.

Doppler shift RF or laser is the only two things that I believe would be appropriate.

Ray

#### Henry_Best

#3
##### Oct 06, 2013, 04:09 am

Quote
50km/h

50K/(60*60) = 139 Meters/Sec.

Doppler shift RF or laser is the only two things that I believe would be appropriate.

Ray

If, as the OP describes, the two cars are travelling at nearly the same speed there won't be much (if any) Dopler shift.

#4
##### Oct 06, 2013, 05:26 am
Home Depot carries laser room measurement instruments, for example
http://www.homedepot.com/p/Bosch-165-ft-50m-Laser-Dist-Measurer-GLM-50/203392595?MERCH=REC-_-SearchPLPHorizontal1-3-_-NA-_-203392595-_-N#.UlDZCtKsjZk
Maybe browse those, find one with a serial interface you can read.

Then, work on an aiming/tracking control, I think that will be the tricky part.
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

#### Paul__B

#5
##### Oct 06, 2013, 06:44 am
Ultrasonic transponder.

The "seeker" sends a "ping" - a short ultrasound burst - and the "target" responds with two bursts.

The distance is calculated by the transit time, but only if the two received bursts are the correct distance apart.  Thus it only responds to "echoes" that are actually from the target, and can handle far more attenuation than if it was looking for a passive echo, so can also use less power and/ or a wider beam.

#6
##### Oct 06, 2013, 07:03 am
50km/hr = 31 mph, gonna be quite bit of wind noise to deal with at that speed too.
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

#7
##### Oct 07, 2013, 06:29 pm
Paul__B, this seems like it would be a viable way to do this, but I haven't seen any projects that actually use ping sensors between two Arduinos.  They always use the reflection.  It seems like you could get a lot greater distance by using the pings directly instead of reflections.  Does anyone know of a project that uses this idea?

#### AWOL

#8
##### Oct 07, 2013, 07:59 pm
Quote
50K/(60*60) = 139 Meters/Sec

sp. "13.88 ms-1
"Pete, it's a fool looks for logic in the chambers of the human heart." Ulysses Everett McGill.
Do not send technical questions via personal messaging - they will be ignored.

#### Paul__B

#9
##### Oct 07, 2013, 10:49 pm

Paul__B, this seems like it would be a viable way to do this, but I haven't seen any projects that actually use ping sensors between two Arduinos.  They always use the reflection.  It seems like you could get a lot greater distance by using the pings directly instead of reflections.

Precisely my point - much greater signal gain that can be shared between a wider beam width, increased range, greater discrimination from ambient noise and possibly, reduced power,

Does anyone know of a project that uses this idea?

Not I, but it should be simply a matter of adapting present ultrasonic ranging approaches.

#### AWOL

#10
##### Oct 07, 2013, 11:05 pm
You could also do a transponder-like approach with a strobe (probably IR) which is triggered at the same time as the ultrasound pulse.
Time-of-flight of the IR pulse is negligible.
"Pete, it's a fool looks for logic in the chambers of the human heart." Ulysses Everett McGill.
Do not send technical questions via personal messaging - they will be ignored.

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