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idbruce
02-20-2012, 01:17 PM
Hello Everyone

Assuming a distance range of up to 3", is it possible to increase the sensitivity of the PING))) Ultrasonic Distance Sensor to 0.001"? If not, then what distance can this sensor be modified to monitor?

Bruce

Duane Degn
02-20-2012, 03:07 PM
You're limited by the wavelength of the ultrasound used.

IIRC it's between 1 and 2 mm.

idbruce
02-20-2012, 03:28 PM
Thanks Duane

Duane Degn
02-20-2012, 03:35 PM
You are welcome Bruce.

Last week I had an echocardiogram. They use transducers that output ultrasound in the 4MHz range. If you could find a higher frequency transducer, you should be able to increase the precision of an ultrasound range finder.

idbruce
02-20-2012, 03:48 PM
Thanks again Duane.

I will have to do an in depth search to see what kind of solutions are actually available for a reasonable cost.

And before anyone mentions "lasers" (not referring to you Duane :) ), let me just say that I am trying to avoid the use of light, because I will be measuring the distance to a photosensitive film. However, I suppose I could use a light source that is outside the wavelength sensitivity area.

Bruce

Bits
02-20-2012, 11:27 PM
Just thinking out loud here....

Could you use 2 pings and fire them at slightly different intervals then differentiate the readings? This may give finer detail than post #2 states.

Perhaps using a spectrum of light that the photosensitive film is not sensitive to also may provide a better measurement.

ctwardell
02-21-2012, 12:00 AM
Bruce,

Is there anything directly behind the film?

I'm thinking maybe a sensor based on capacitance.

C.W.

RobotWorkshop
02-21-2012, 12:27 AM
Another option may be to try this propeller powered sonar sensor:

http://gadgetgangster.com/find-a-project/56?projectnum=138

It appears to be on sale at the moment and you may be able to modify it to suit your needs.

Robert

Duane Degn
02-21-2012, 01:09 AM
Another option may be to try this propeller powered sonar sensor:

http://gadgetgangster.com/find-a-project/56?projectnum=138

It appears to be on sale at the moment and you may be able to modify it to suit your needs.

Robert

I was thinking of the same thing earlier today. I wonder if those transducers could be driven at a high enough frequency to make a significant difference in its precision. I know piezo buzzers work best at certain frequencies but they will also work outside their optimal range but at lower volume. Maybe the ultrasound transducers could be driven at a higher freqency giving higher precision with a shorter range.

Phil Pilgrim (PhiPi)
02-21-2012, 01:35 AM
Any given ultrasonic transducer will resonate at one frequency and one frequency only, given its extremely high Q factor. You just can't use 40kHz transducers at 200kHz, for example, and expect them to work.

Bruce, assuming your film is not sensitive to infrared, an IR distance sensor like this one, might be your best bet:


http://www.parallax.com/StoreSearchResults/tabid/768/txtSearch/distance/List/0/SortField/4/ProductID/776/Default.aspx

-Phil

idbruce
02-21-2012, 02:35 AM
I must say that I never thought this thread would get so many responses.

I thank you all for your support.

And for those that responded, it appears as though Phil has the closest solution.

@Phil

The spectral sensitivity graph for the film drops off the chart at approximately 715 nm, and the Sharp GP2Y0A21YK0F IR Sensor datasheet specifies a wavelength of 870 plus/minus 70 nm, so I assume it would work without giving me any grief. However I cannot find any information that specifies the accuracy of this sensor. Just how accurate are these sensors?

Bruce

Duane Degn
02-21-2012, 02:36 AM
Any given ultrasonic transducer will resonate at one frequency and one frequency only

Good to know. You probably just saved me a bunch of time because I was considering trying to drive one at other frequencies. I'd been thinking about it ever since the echocardiogram.

Phil Pilgrim (PhiPi)
02-21-2012, 02:44 AM
Bruce,

For "accuracy", you will probably have to calibrate it. For "precision" and "repeatability', it should be spot on, since I assume the target material and orientation will be the same every time. In any event, at only $11, testing it will be cheap.

-Phil

idbruce
02-21-2012, 03:06 AM
Phil

Thanks for the input, I definitely appreciate it.

Bruce

ctwardell
02-21-2012, 04:06 AM
Bruce,

I don't think the GP2Y0A21YK0F will have resolution anywhere near what you want, I recall getting resolutions on the order of a 1/2 inch or so at best on a robot.

You might want to try to locate a GP2Y0AH01K0F high precision sensor, but even it only claims 0.1mm (~0.004 inch) resolution in the range of 4.5 to 6mm.

Here a a link to the PDF, but they don't stock the item:

http://media.digikey.com/pdf/Data%20Sheets/Sharp%20PDFs/GP2Y0AH01K0F.pdf

C.W.

Publison
02-24-2012, 05:05 PM
Bruce,

This is a device we used to use to focus the Z-Axis on one of our Gerber Phottoplotters to determine the height above .004 film, .007 film, and glass plate.

http://www.massa.com/Datasheets/E-188-220%20Datasheet%20090922.pdf

J (http://www.massa.com/Datasheets/E-188-220%20Datasheet%20090922.pdf)im

idbruce
02-24-2012, 05:11 PM
Publison

Thanks for the link and the previous description of the aperture plate.

Bruce

Publison
02-24-2012, 05:18 PM
Bruce,

I just wish I could find the 2-3 boxes of my Gerber documents so I could provide some supporting documentation, (schematics, etc).

Shouldn't take a month or so. :)

Bits
02-24-2012, 08:30 PM
Not sure what the entire spectrum that the film is sensitive to but these decent lasers (http://search.digikey.com/us/en/products/OPV380/365-1145-ND/761808) and detectors (http://search.digikey.com/us/en/products/LPT 80A/475-1419-ND/1227971) can detect small distances and calibration is a snap.

I use a comparator on the detector so that the sensitivity can be set. If you wish I could provide a schematic.

Ron Czapala
02-24-2012, 08:40 PM
Not sure what the entire spectrum that the film is sensitive to but these decent lasers (http://search.digikey.com/us/en/products/OPV380/365-1145-ND/761808) and detectors (http://search.digikey.com/us/en/products/LPT 80A/475-1419-ND/1227971) can detect small distances and calibration is a snap.

I use a comparator on the detector so that the sensitivity can be set. If you wish I could provide a schematic.

Those really look interesting - I would love to see the schematic. What is the maximum distance you've tried?

Bits
02-24-2012, 09:06 PM
Currently I am using it for a client of mine whose design requires a distance of 3" away through a slot ~ 20 thousands wide. Impressive in my opinion! There are 1 to 2 other lasers that I believe contains a crude type of collimating lenses.

opps - ill provide a schematic soon. I am at "my main" office, ill be at my "home" office tonight.

idbruce
02-24-2012, 09:26 PM
@Bits

Thanks for the input.


The spectral sensitivity graph for the film drops off the chart at approximately 715 nm

So I would imagine that these devices would be okay. As for the schematic, well I am always interested in seeing a nice little schematic for accomplishing a given task. As they say, "A picture is worth a thousand words". :)

Thanks again for the input Bits.

Bruce

Bits
02-25-2012, 12:58 AM
Here is the schematic. Its pretty simple. Basically you have to keep in mind that the base of the photo-transistor is the laser light itself and the emitter / collector is listed on the data sheet.
J1 and J2 are for the laser and photo-transistor. U1 is used as a comparator, change the voltage that triggers by adjusting the pot. I attached LASER_SEN_A and LASER_SEN_B to i/o pins on the propeller.
89984

idbruce
02-25-2012, 01:17 AM
Bits

Thank you very much for the schematic. I appreciate your effort and sharing.

Bruce

Ron Czapala
02-25-2012, 01:45 AM
Bits,

Thanks for the schematic.

Am I right in assuming that the laser is driven by 3.3V with a series resistor of 166 ohms (I don't see a symbol for the laser just the word laser)

Bits
02-25-2012, 01:55 AM
Bits,

Thanks for the schematic.

Am I right in assuming that the laser is driven by 3.3V with a series resistor of 166 ohms (I don't see a symbol for the laser just the word laser)

Yes, J1 & J2 are used for the laser (pins 1 & 2) and the detector (pins 3 & 4). I specifically had to use 3.3V due to board real-estate and cost but, 5 volts would work as well. A resistor re-calculation would be needed however.

__red__
02-25-2012, 12:37 PM
I'm also watching this thread with interest as I want to attempt to measure the distance between a 1/64" end mill and the surface of a pcb for a pcb milling machine I'm building.

Most designs use a "foot" but I don't trust myself to build one with enough level of accuracy.