Society of Robots - Robot Forum
Electronics => Electronics => Topic started by: Trumpkin on July 08, 2008, 03:13:52 PM
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Looky what I found! http://www.instructables.com/id/DIY-Force-Sensitive-Resistor-FSR/ I certainly never thought that could be done with such simple materials. does anybody have Ideas of what you could use it for?
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Now that's pretty cool. It would be very easy to use something like that inside a gripper.
I seem to remember seeing something similar made with window screen. Can't remember what the middle conductor material was. They put it on a punching bag or something like that. I'm going to have to look that up to see if I can find it.
Edit: I found it (http://www.fluidforms.at/de/CassiusHow.php), and it's virtually identical to what you posted. Wonder where you can get large sheets of that foam...hmm...
Another Edit: Wow, 10+ pages of conductive foam in the Google shopping section. This inter-web thing never ceases to amaze me.
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http://www.altex.com/product_info.php?products_id=6242 pretty cheap stuff, I wonder what thickness is the best.
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Well, I gather the thickness would simply define the resistance at rest vs. resistance while compressed. (similar to a photocell)
So, (all theoretical numbers here), a FSR with 1" thick foam might have an "at rest" resistance of 100M Ohm and a "compressed" resistance of 1MOhm, while a FSR with 1/8" thick foam might have an "at rest" resistance of 100k ohm and a compressed resistance of 1000 ohms.
This is truly groundbreaking for me. I bet I could build myself a nice little pressure pad for my Halloween display. I just need to find myself a rather large and thin sheet of that foam.
Any ideas on a conductive adhesive? They say in the instructable you find that the adhesive can interfere with the conduction between the foam and the copper board.
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it couldn't hurt to try conductive adhesive, i googled it and one of the first results was this http://scientificsonline.com/product.asp?pn=3035852&sid=2008FS&eid=2008FS&mr:trackingCode=C8DE8CFA-D14D-DD11-AFF6-000423C27502&mr:referralID=NA&bhcd2=1215724616
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I wonder how varying thicknesses of the conductive adhesive would affect the accuracy of the sensor. I found some conductive double sided adhesive sheets, but they're super expensive. Will keep looking.
I'm definitely putting this sensor on my build list.
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This is actually an old idea - I first saw this like 10 years ago ;D
IC's and other electronics often come with that conductive foam as part of the packaging. I always keep some around just in case.
To maximize the signal, follow the schematic and equation as if it was a photoresistor:
http://www.societyofrobots.com/schematics_photoresistor.shtml
(but instead of light intensity, its foam compression %)
You may have a problem with sensor hysteresis though . . . google that for more info ;)
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Oh, hysteresis, like when I burned my hand real good with the soldering iron, or when my daughter's kitten jumped on my face in the middle of the night? :D
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no, thats hysteria ;D
(and perhaps a hysterectomy for the cat)
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The cat got a smack-terectomy. >:(
Seriously though...
I can see how the foam would not perform consistently. Each compression would change the characteristics of the foam and thus the sensor itself. I'm good with that. If I need something more reliable (like for grippers), I'll just shell out the bucks for a commercial FSR.