physical contact sensing alternatives
What different alternatives are there to sense a physical contact with an hollow non-conductive cylinder? Think soda bottle, pill bottle, or a bit of hosing.
I would like forgo putting a micro switch that would interrupt the surface.
I want to sense a person or any part of person, with or without clothing or gloves.
I want a cheap solution, without much fuss or circuitry. If I can whip the prop into doing the work of another chip (adc, capacitive sensor chip), I would be happiest.
I'd like it to be simple enough to replicate 3 or 4 times and still leave·lots of·propeller/cogs/pins.
I·haven't found a capacitive solution, though I'm sure it exists.
I have looked at using a·LED in reverse to·notice a·touch, and may do that if it isn't·particularly sensitive to·ambient light. But it does disturb the surface and·may·not be·able to withstand misuse.
Non conductive material is a poly plastic. Tape solutions applied to the surface·are ok, if I can find one.
Maximum frequency looks under 50 hertz. Duration may be as little as 1/10 of second, but on the order of a couple pounds force.
Can in place; kick it. (Thanks)
I would like forgo putting a micro switch that would interrupt the surface.
I want to sense a person or any part of person, with or without clothing or gloves.
I want a cheap solution, without much fuss or circuitry. If I can whip the prop into doing the work of another chip (adc, capacitive sensor chip), I would be happiest.
I'd like it to be simple enough to replicate 3 or 4 times and still leave·lots of·propeller/cogs/pins.
I·haven't found a capacitive solution, though I'm sure it exists.
I have looked at using a·LED in reverse to·notice a·touch, and may do that if it isn't·particularly sensitive to·ambient light. But it does disturb the surface and·may·not be·able to withstand misuse.
Non conductive material is a poly plastic. Tape solutions applied to the surface·are ok, if I can find one.
Maximum frequency looks under 50 hertz. Duration may be as little as 1/10 of second, but on the order of a couple pounds force.
Can in place; kick it. (Thanks)
Comments
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Post Edited (Ken Peterson) : 5/31/2008 3:02:23 AM GMT
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JMH
-Phil
Along similar line as Ultrasonic, you might be able to do something with the resonate frequency of your container. More description of your container might be in order, but the basic idea is this.... Use two piezo transducers, one as a microphone, and the other as a speaker and sweep the frequency to the piezo speaker. Monitor the "sound signature" across the swept frequencies on the piezo microphone. Any difference or change within the container either by adding something, taking away something, or even nearby changes can affect the characteristic "sound signature"... If there is a significant change between the sound signatures from one sample to the next, you can use that information to determine your actions.
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Beau Schwabe
IC Layout Engineer
Parallax, Inc.
Phil, I like that chip but want to save my bucks for a qfn propeller -- I want to make a prop system board that's narrower than 3/4 inch and·as cloase to that long as well. Plus I'm thinking about a mems 3axis·chip already and and and and...
What recession?
Beau: I'd say, but people would just make fun of me. Or worse, not. I don't think ultrasonic would work, as once it's picked up, it's picked up and stays there. I just want to know when its picked up in the right places.
Post Edited (Fred Hawkins) : 5/31/2008 4:17:12 AM GMT
Got it working, sort of. But after I tried it with a 6 foot wire, it became noisy. The indicator LED would fire often as long the prop plug was connected. Taking the plug off, it would light up about every 10 seconds. And I had to set the threshold much higher to $77 or so.
I think I know now why the internet has lots of moaning about how temperamental this is. High fiddle factor, methinks.
PCB-Based Capacitive Touch Sensing With MSP430
http://focus.ti.com/lit/an/slaa363a/slaa363a.pdf
MSP430 Capacitive Single-Touch Sensor Design Guide
http://focus.ti.com/lit/an/slaa379/slaa379.pdf
That's opposite from what your spin program uses. What advantage, if any, comes from tying the resistor to vcc?
Fred
If you want to run it 6' away from the Prop, have you tried connecting with coax? The shielding might help.
Ken
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My next pass will be an optimized pad -- a 1/2 inch copper disk surrounded by a ground field. If I read Quantum's Touch Secrets (ap note AN-KDO2) rightly, the field is generated at the margins heading for the ground. TI suggests using a 5M resistor which may be pass 3.
This pdf may be useful: http://www.silabs.com/public/documents/tpub_doc/anote/Microcontrollers/Small_Form_Factor/en/an338.pdf
Post Edited (Fred Hawkins) : 6/7/2008 7:23:04 PM GMT