"Ruggedized" PING))) sensor mounting?

Vern Graner

I'm working on a project that wil be placed in a children's museum. It makes use of PING))) sensors to detect hand positions to teach about sonar sound.

Since the ping sensors will be used by kids, I need to find a way to protect the sensors from kids poking their fingers into the transducers. I tried recessed mounting the ping behind a piece of acrylic with a grid of holes in front of it (kinda like a speaker grill) but that caused the sensor to mis-read (i.e. shows items very close to the sensor when there are none).

Anyway, I was hoping someone else had gone down this road and might have advice on how to mount the PING))) sensor in such as way that it

1) works and ranges properly and

2) is fairly well protected from kids fingers.

Any help appreciated!

Vern

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Phil Pilgrim (PhiPi)

You didn't mention how far back from the plexiglas grille you mounted the Ping))). Getting it closer should help. Also, if you use a common grille for the two transducers, you might add a baffle between them to keep grille echoes from the transmitter from ever reaching the receiver. Also, holes-in-plexi represents a pretty solid "target". Something "stealthier", like screenwire, may work better.

-Phil

Post Edited (Phil Pilgrim (PhiPi)) : 3/10/2008 9:16:08 PM GMT

Vern Graner

Phil Pilgrim (PhiPi) said...
You didn't mention how far back from the Plexiglas grille you mounted the Ping))).

I've attached a picture of the Plexiglas window to better illustrate the method of mounting. The plexi is 1/4" thick. We drilled down 3/4 of the way through the plexi and then used a small drill bit to make a pattern of holes. I also included some pictures of how it looks when the LEDs are lit.

The panel is supposed to light up concentric rings of LEDs in proportion to your hand's distance from the panel. I have the code working fine with the sensor sitting on the desk, but the moment I place the sensor behind the "grill", it's readings become all close to "zero distance" regardless of the distance of any object in front (i.e. hand position).

You think this might be caused by cross-talk from the Plexiglas?

Vern

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Vern Graner CNE/CNA/SSE    | "If the network is down, then you're
Senior Systems Engineer    | obviously incompetent so why are we
Texas Information Services | paying you? Of course,if the network
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Austin Office 512 328-8947 | you, so why are we paying you?" ©VLG

Phil Pilgrim (PhiPi)

Hmm, I'm surprised that doesn't work. The only thing I can think of is that there's sound conduction through the plexi that's getting picked up prematurely by the receiving transducer. The 750us "holdoff" time should eliminate this, though, unless the plexi continues to resonate beyond that time.

Frankly, I'm stumped.

-Phil

David H.

I haven't worked with these much, but could you step it back from the plexiglass, and drill two larger holes that would be harder for a finger to reach through? That way it would have more of a clear view.
Good luck with the project, and I think the kids with enjoy it.

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David


There are 10 types of people in this world,...
Those that understand binary numbers, and those that don't!!!

Post Edited (David H.) : 3/11/2008 8:06:56 PM GMT

Vern Graner

David H. said...
I haven't worked with these much, but could you step it back from the plexiglass, and drill two larger holes that would be harder for a finger to reach through? That way it would have more of a clear view.

This was an idea we discussed, i.e. making small "tubes" and placing the sonar transducers behind those. The problem is the tubes resonate (i.e. "ring" like a bell) right after the pulse is sent (think "wind chime" tubes). The resonance results in false readings when the hold-off delay releases and the receiver "hears" the lingering signal in the resonation of the tube..

I suppose I could try and make the tubes less resonant by coating the insides with cloth, or foam or some such, but I still end up with an opening I have to protect from curious fingers, so I'm back to some sort of grill or mask that again might interfere with the signal.

David H. said...
Good luck with the project, and I think the kids with enjoy it.

You spelled "destroy" wrong...

Vern

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Vern Graner CNE/CNA/SSE    | "If the network is down, then you're
Senior Systems Engineer    | obviously incompetent so why are we
Texas Information Services | paying you? Of course,if the network
http://www.txis.com        | is up, then we obviously don't need
Austin Office 512 328-8947 | you, so why are we paying you?" ©VLG

Post Edited (Vern) : 3/11/2008 10:15:11 PM GMT

Dgswaner

How about you play a little trick on them... do you have the option of mounting the ping above the panel? you could change the distances so that it lights up in the same manner. and they might not even know that it's actually reading the distance from above. They won't bother a sensor they don't know exists.

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"A complex design is the sign of an inferior designer." - Jamie Hyneman, Myth Buster

DGSwaner

Post Edited (Dgswaner) : 3/11/2008 10:12:28 PM GMT

Phil Pilgrim (PhiPi)

Kid have two hands. They'll figure it out and be scarred for life from knowing they were tricked! I would suggest mounting it vertically, though, to keep snot, drool, and soft drinks out.

-Phil

Dgswaner

lol, yes I suppose your right!

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"A complex design is the sign of an inferior designer." - Jamie Hyneman, Myth Buster

DGSwaner

Searider

I wonder if you made a short tube 1/2" or so and filled it with Open cell foam. or even a multiple layers of cloth. The high freq might get through. I wonder how much cloth you can PING through ?

Ugha

I know its a bit late to consider this... but what about IR ranging instead? You could protect the IR transmitter/receiver far
easier than a ping.

Vern Graner

Ugha said...
I know its a bit late to consider this... but what about IR ranging instead? You could protect the IR transmitter/receiver far
easier than a ping.

The exhibit is to demonstrate sound, both sonic and ultrasonic, hence the PING))) sensor. If I could use an IR ranger I could do it without making any opening in the front panel and that would really be ideal, but this is a display to demo sonar.

Vern

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Vern Graner CNE/CNA/SSE    | "If the network is down, then you're
Senior Systems Engineer    | obviously incompetent so why are we
Texas Information Services | paying you? Of course,if the network
http://www.txis.com        | is up, then we obviously don't need
Austin Office 512 328-8947 | you, so why are we paying you?" ©VLG

Phil Pilgrim (PhiPi)

Vern,

What are you trying right now? I'm curious about any progress you might be making to eliminate the errant echoes...

Thanks,
-Phil

Zoot

Low-density ceramic tubes are often used for focusing and/or physically offsetting sonar transducers -- the tubes direct the sound waves without impeding them and without reflecting off the walls of the tube (essentially the walls of the soft ceramic tube absorb sound that it might otherwise reflect back at the transducer. The old Hero-1 robots had these on the transducers.

You can get a similar result using the softest PVC you can find cut to size so it fits around the transducers (not too tightly). Lining with any sound absorbent material will help w/echoes (i.e. thin felt). You suggested this, but don't fill the tubes, line them. You can get away with very long tube lengths (9"-18") -- given the small diameter of the transducers on the ping, and that kind of length, I would think kids won't be able to get fingers to Ping)))s. I think the only possible issue is that someone could put an object in (marble, pocket lint, boogers, etc). You would also try rolling very narrow cones (so that the aperature at the display end is wider than the transducer end) out of a think backing lined with felt (perhaps very very thin sintra with very thin felt cemented on before cutting).

The other thing to try is to hit a professional audio supply house (if you have one in your area) -- you can get "aurally transparent" grilles (i.e. foam, cloth, weaves, etc.) that may do the trick -- and probably for not much $$. I wouldn't spend time experimenting with off the shelf cloth/foams/etc. -- if the material is not designed to be aurally transparent, then chances are it won't be, esp. at the high frequencies of sonar.

Very cool exhibit. The kids will love it. Have you all thought about different kinds of gloves for kids to experiment with? Put in a bin near the exhibit? For example, a soft fuzzy glove (like a care waxing glove) will probably reflect almost no sonar. A glove with a hard plastic disc on the palm will reflect really well. An ungloved hand will reflect pretty well, but not always.

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Vern Graner

Phil Pilgrim (PhiPi) said...
What are you trying right now? I'm curious about any progress you might be making to eliminate the errant echoes...

We had our weekly Robot Group Meeting last night and I discussed it with some of my fellow Roboteers. It was suggested I try using a fan grill built from wire such as the one in the attached picture.

These fan grills are available in 40mm, 60mm and 80mm sizes so I should be able to find one that would be able to cover the PING sensor without being so large as to cover the rest of the panel. The hope is that the round surfaces of the wire used to make the grill will better pass the sound without fear of flat, parallel surfaces causing resonations.

Also, I'm hoping the wider bar spacing will stopping kids fingers from reaching the more fragile metal screen at the front of the ping sensor.

These fan grills are cheap and easily found so I will be testing the theories expressed here this weekend. Wish me luck!

Vern

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Vern Graner CNE/CNA/SSE    | "If the network is down, then you're
Senior Systems Engineer    | obviously incompetent so why are we
Texas Information Services | paying you? Of course,if the network
http://www.txis.com        | is up, then we obviously don't need
Austin Office 512 328-8947 | you, so why are we paying you?" ©VLG

Vern Graner

Zoot said...
Low-density ceramic tubes are often used for focusing and/or physically offsetting sonar transducers -- the tubes direct the sound waves without impeding them and without reflecting off the walls of the tube (essentially the walls of the soft ceramic tube absorb sound that it might otherwise reflect back at the transducer. The old Hero-1 robots had these on the transducers.

I remember that the surface surrounding the sonar sensor on the hero had foam rubber around it! (see attached picture of Hero-1 sonar unit) I had forgotten about that till you mentioned it! I imagine they were dealing with similar reflection issues. Hmm might be something to consider doing.

Zoot said...
You can get a similar result using the softest PVC you can find cut to size so it fits around the transducers (not too tightly). Lining with any sound absorbent material will help w/echoes (i.e. thin felt). You suggested this, but don't fill the tubes, line them. You can get away with very long tube lengths (9"-18") -- given the small diameter of the transducers on the ping, and that kind of length, I would think kids won't be able to get fingers to Ping)))s. I think the only possible issue is that someone could put an object in (marble, pocket lint, boogers, etc). You would also try rolling very narrow cones (so that the aperture at the display end is wider than the transducer end) out of a think backing lined with felt (perhaps very very thin sintra with very thin felt cemented on before cutting).

I can see you're thinking along the same lines. marbles, fingers, boogers.. even chewing gum! Any opening is a weakness and a repair/safety concern.

Zoot said...
The other thing to try is to hit a professional audio supply house (if you have one in your area) -- you can get "aurally transparent" grilles (i.e. foam, cloth, weaves, etc.) that may do the trick -- and probably for not much $$. I wouldn't spend time experimenting with off the shelf cloth/foams/etc. -- if the material is not designed to be aurally transparent, then chances are it won't be, esp. at the high frequencies of sonar.

I did try some cloth over the top of the sensor and the ping sensor worked fine though it. I just used a simple household hand towel. The problem is that any cloth would get shredded pretty quick. Also, the materials all have to be "cleanable" and they use a spray disinfectant / glass cleaner to make it sanitary (as much as possible). I don't think they would like to have to remove little cloth pieces and wash them daily.

Zoot said...
Very cool exhibit. The kids will love it. Have you all thought about different kinds of gloves for kids to experiment with? Put in a bin near the exhibit? For example, a soft fuzzy glove (like a care waxing glove) will probably reflect almost no sonar. A glove with a hard plastic disc on the palm will reflect really well. An ungloved hand will reflect pretty well, but not always.

This is a very cool idea... Maybe have small pieces of material on lanyards that can be held up in front on the display.. A piece of fuzzy fake fur on disk... a piece of hard plastic.. a piece of opaque plastic and a piece of transparent plastic. Hmm this is an interesting idea. Thanks!

Vern

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Vern Graner CNE/CNA/SSE    | "If the network is down, then you're
Senior Systems Engineer    | obviously incompetent so why are we
Texas Information Services | paying you? Of course,if the network
http://www.txis.com        | is up, then we obviously don't need
Austin Office 512 328-8947 | you, so why are we paying you?" ©VLG

Zoot

Re: paper towel fabric, etc. Aural grill cloth, mesh, foam are available that are washable, cleanable, hypoallergenic. Like I said, you won't find this off the shelf anywhere -- you'll need to hit an audio supply house either locally or online (the former has the advantage in that you need so little they may be give you some swatches of various kinds gratis).

This is such a cool exhibit idea -- keep everyone posted once you've got it up and running.

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MSDTech

If you're looking at acoustic foam, you might be able to use the replacement foam earpieces for headphones. I am using them to cover an ultrasonic transducer and have seen no effect on its performance. The are about $5 at your local radio shack and come in several sizes.

Vern Graner

MSDTech said...
If you're looking at acoustic foam, you might be able to use the replacement foam earpieces for headphones. I am using them to cover an ultrasonic transducer and have seen no effect on its performance. The are about $5 at your local radio shack and come in several sizes.

The key here is ruggedized. Acoustic foam, paper towels, cloth etc. all would be shredded in a matter of days. Think "playground equipment". Kids can walk right up (and are encouraged to walk right up!) to the kiosk and interact with the sensor. Kids are tough on this sort of thing.



Vern

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Vern Graner CNE/CNA/SSE    | "If the network is down, then you're
Senior Systems Engineer    | obviously incompetent so why are we
Texas Information Services | paying you? Of course,if the network
http://www.txis.com        | is up, then we obviously don't need
Austin Office 512 328-8947 | you, so why are we paying you?" ©VLG

Vern Graner

FAN GRILL TESTING RESULT: EPIC FAIL

For those of you that have been following this thread, we tried the silver fan grills and they are NOT transparent to sonar. as a matter of fact, they work fine as reflectors! You can hold them in front of the sonar unit and it "sees" the grill as a solid surface! [noparse]:sigh:[/noparse] I'm still looking for a solution. when I find one I'll let you guys know.

Vern

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Vern Graner CNE/CNA/SSE    | "If the network is down, then you're
Senior Systems Engineer    | obviously incompetent so why are we
Texas Information Services | paying you? Of course,if the network
http://www.txis.com        | is up, then we obviously don't need
Austin Office 512 328-8947 | you, so why are we paying you?" ©VLG

Post Edited (Vern) : 3/17/2008 6:13:31 PM GMT

Zoot

Well, what about the wire mesh that covers the Ping))) transducers already? It's wire mesh, it's obviously transparent to sonar. Maybe a square foot in the parts bin would cover you.

Yo, Parallax folks -- what is the wire mesh on the Ping))) covers and where did you get it?

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Ugha

I actually thought about that mesh... I know it'd be expensive and kind of wasteful... what about a second Ping and removing
the Mesh from it and using that?

Searider

Check out these transducers. They look solid.
http://www.hobbyengineering.com/H4095.html

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Searider

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Searider

You also might check out transducers made for the automotive industry. There bound to be pretty rugged.

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Searider

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Vern Graner

Searider said...
Check out these transducers. They look solid.
http://www.hobbyengineering.com/H4095.html

Thanks! I found the spec sheet for the one shown there and compared it to the one for the part on the Parallax PING.

Looks like it might be possible to replace the transducers on the PING with some of these solid aluminum ones! Hmm.. Of course warranty void blah blah..

Heres the two PDF documents with the specs in case anyone wants to have a look:

Part # 400ET R180 sensor module from Hobby Engineering

Part # CUR17G1A-40 used on PING))) sensor from Parallax

Vern

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Vern Graner CNE/CNA/SSE    | "If the network is down, then you're
Senior Systems Engineer    | obviously incompetent so why are we
Texas Information Services | paying you? Of course,if the network
http://www.txis.com        | is up, then we obviously don't need
Austin Office 512 328-8947 | you, so why are we paying you?" ©VLG

Vern Graner

Zoot said...
Well, what about the wire mesh that covers the Ping))) transducers already? It's wire mesh, it's obviously transparent to sonar. Maybe a square foot in the parts bin would cover you.

The mesh is relatively fragile. In the "Thereping" instruments, we had kids banging on the sensors as a side effect of playing the instrument.

Impact has caused the metal mesh to recede into the tube when pressed with a finger or hit. I've also seen holes torn in the mesh by people wearing rings while playing the instrument.

Its looking like the aluminum transducers might be the ticket, but I'll have to order them to find out (and sacrifice one ping sensor to test). More delays! :[noparse]:sigh:[/noparse]:

Vern

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Vern Graner CNE/CNA/SSE    | "If the network is down, then you're
Senior Systems Engineer    | obviously incompetent so why are we
Texas Information Services | paying you? Of course,if the network
http://www.txis.com        | is up, then we obviously don't need
Austin Office 512 328-8947 | you, so why are we paying you?" ©VLG

Post Edited (Vern) : 3/18/2008 11:13:49 PM GMT

Phil Pilgrim (PhiPi)

Hmm, interesting idea. The pin spacing is a little different, but that's not fatal: you can crimp the pins in a little to make it fit. The front of the transducer is a "diaphragm", according to the datasheet. Its thickness will determine how resistant it is to pokey little fingers.

-Phil

Vern Graner

Seems the folks at Parallax have come up with a possible solution to this issue! Check it out!

The new H2O PING sensor

Cool!

Vern

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Vern Graner CNE/CNA/SSE    | "If the network is down, then you're
Senior Systems Engineer    | obviously incompetent so why are we
Texas Information Services | paying you? Of course,if the network
http://www.txis.com        | is up, then we obviously don't need
Austin Office 512 328-8947 | you, so why are we paying you?" ©VLG