Any designs for a cheap x-y position sensor?

I don't know how often a camera supplies an image. But, stitching shouldn't be a problem. I've done spline fit and stitching software for some really 'distorted' images caused by views from two different positions and it is surprising the results possible. - if you're willing to stretch the final image, too.

t.net ---

Luckily, x-y should be all that's necessary. If I get into x, y, z I'll also get into 'tilt' and end up with 6 axes to deal with! x-y simulates the 'flat' earth, so should be sufficient. Better than not knowing where you're at or how fast you're moving.

Presumably the object being imaged occupies many pixels, so there is lots of data for signal averaging. And one could use lots of cameras.

--

John Larkin                  Highland Technology Inc
www.highlandtechnology.com   jlarkin at highlandtechnology dot com   

Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom timing and laser controllers
Photonics and fiberoptic TTL data links
VME  analog, thermocouple, LVDT, synchro, tachometer
Multichannel arbitrary waveform generators

good catch.

It would be easy to put a 'marker' on the unit and as the Operator moves around, spot it in the camera's field of view. Live with the camera rep rate and simple interpolate to find where the system is at WHEN the system asks.

starting to lean that way, too. gross, numbers but getting pretty cheap. Plus have a record of EXACT terrain for archives.

Lugging extra stuff out into the field is not so good. But, thanks for triggering the brain! Ok, put two posts, each generating a pure known tone. Then simply count the standing waves as I walk around. Voila! relative 'optical' mouse, but done using audio.

Tones near 30kHz travel well, we don't hear. and have a wavelength of around 1/2 inch! so I could easily digitize two to 8 pulses per inch !

Downside is losing signal. ouch. and worse multiple path! that would really distort position information. But then again the price tag is not too bad - pure sound source, turn ON and leave alone and built-in mikes with some SW to sort it out. Including a potential 'calibration' step for that time of day, that altitude, and that humidity. hmmmm.... not bad.

The cheapest USB color camera on ebay/amazon is $1. I've run 75 feet to a camera, two active USB extenders and some passive cables. Ethernet cams can run any distance. The software will be the hard part.

--

John Larkin                  Highland Technology Inc
www.highlandtechnology.com   jlarkin at highlandtechnology dot com   

Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom timing and laser controllers
Photonics and fiberoptic TTL data links
VME  analog, thermocouple, LVDT, synchro, tachometer
Multichannel arbitrary waveform generators

Great !!!

I hope you will post here or at Hack-a-day on your results.

hamilton

The speed of sound doesn't depend on pressure, just temperature and mean molecular weight.

The real downside is wind and temperature changes. Unlike light, sound is an oscillation in a physical medium, and when the medium moves, the rest-frame speed of sound changes. The speed of sound at 20C is about

343 m/s (per ), or about 770 mph. Thus a 2-mph breeze will cause a phase error of 0.25%. Similarly, a 2-degree temperature difference will cause the speed of sound to change by 0.5 * 2/293 = 0.34%. (The factor of 1/2 comes from the binomial expansion of the square root--v goes as sqrt(t)).

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.net

m

ARRRGGG! I don't mind making mistakes, I just hate to make them so publicly!!

The angular width of the beam will be constant! therefore the time the beam takes from start to end will be constant - no matter where you are along th beam's line - unless the beam's width is a parallel set, then as a function of distance away there will be a difference in time from start to end. Well, at least I can use the start of beam and end of beam to deterine the CENTER of the beam accurately. Then, just need two beams, just like VOR.

thanks for the URL. specifically says "..for ideal gases..." does not depend on pressure, Wonder how much speed does change with pressure, must be small. Isn't atmosphere close to ideal gas?

for breeze, can sit still and watch 'motion' to validate measurements, or have software do a warning when the rms distance measurements go frenetic. Temp can monitor temp and 'adjust' maybe. but will crunch the numbers to find the impact. Seems like further away, the less accuracy, duh! Hopefully, a whole field will be scanned and finished way before the temp changes more than 6F, less than 3C

If you put some good-quality retroreflecting tape (e.g. ScotchLite 7610) on two poles, it will return an incident beam into a cone of about 0.5 degree half angle, which gets you about a 70 dB signal level improvement vs. just painting them white. A laser rangefinder will then do the same job as the cables.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.net

Actually, true laser beams diverge like mad. They're Gaussian. You can adjust the collimating lens and the angle generating lens to open up the angle as far as you want. A modern diode laser, before it hits its collimating lens, has a 10' x 40 degree elliptical pattern. In fact, the cheaper the diode, the more the ellipse.

You then use a optical bandpass filter, either colored plastic, or a multilayer dielectric filter(cheap ones for 632.8 nm aka 633 abound) to get your SN ratio through the roof.

Phil beat me to it on the Scotchlite (TM) tape. White retro- reflective bike reflectors also return a strong cone.

Neat thing about the Scotchlite, the detectors can be at the lasers.

Just spin a 45' mirror on a motor shaft above a vertically oriented laser. Use front surface mirrors to get rid of the ghost beams in the timing.

If it cost you more then 60$ to make each laser station, I'd be shocked.

Steve

Robert Macy a écrit :

Have 4 emitter-receivers, 1 mobile and 3 "base stations". Then close the loop of your mobile gizmo through successively each of the ground units, so as to have the loops oscillating. Oscillation frequencies will depend on the distance to each base station, from which you can extract the position.

1 foot is about 2ns round trip, so it's probably workable without too much efforts and you can have an easy try with COTS RF gizmos...

--
Thanks,
Fred.

s in

e

Can you share details? AC or DC B field? Flux gate magnetometer as detector?

George H.

Yep, this is the only low-cost hardware that'll do it. You can get a little fancy, use a fluorescent target and a flashing UV illuminator source to help declutter the images.

The Gollum scenes in LOTR were shot with this kind of digitization, of an actor in a bodysuit studded with targets. They decluttered the images with a large studio painted black...

On 9/18/2012 10:31 AM, Robert Macy wrote: >specs >1. RELATIVE position once START is ok. Then can RESET and start again >from another marker. >2. over an area of approx 100 ft by 100 ft

You did not mention what surface you would be dealing with.

hamilton

ain

thought I alluded to it by mentioning portable, field, rough terrain. in other words down by the river, up the side of a mountain, along a arroyo floor, edge of a ??, out along the edge of a cliff, that kind of 'rough' terrain.

AC fields, although DC doesn't take much current ;)

flux gates are waaay too noisy to get 125 ppm rms