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Tired of paying exorbitant amounts for a simple analog pressure sensor? Well here is an easy smeasy way to make an incredibly cheap analog pressure sensor. This pressure sensor won’t be terribly accurate in terms of measuring precise weight or things of this nature, though it can be calibrated somewhat and if you choose to coat it in something like Plasti Dip some of the variables such as humidity and the like can be minimized. However, what this analog pressure sensor is best for is for creating things like bumper sensors that can read variable levels of pressure and various other touch / pressure sensor applications. Find more interesting things like this in the How-to section of my website TodayIFoundOut.com
Materials:
- Any static dissipative foam (If you’ve ever ordered any IC chips, you probably have some lying around. IC’s are often set in this foam for shipping.) or if you don’t have any, you can pick it up from a variety of places, such as this
- Wire
- (optional) Plasti Dip Rubber Coating
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Step 1:
Cut the foam to the size you like. You can cut it quite small and still get a good range of resistance levels. The foam in this picture is cut to less than half an inch square and about 1/4 inch thick; once completed these two each produce a range of around 2.6K Ohms down to 400 Ohms when squished completely.
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In my hands, when I built a version that had the conductive foam sandwiched between sheets of aluminium (ie very good surface area), the resistance jumped around a lot, even when no force was applied or the same force was applied.
I am wondering whether there is much difference between different types of conductive foam?
Aren't they just graphite in polyurethane foam?
Any ideas to make the sensor more stable?
cheers
hmmm. ya i can't think of anything else here why this might be happening. it seems like even if you have the leads hooked up to the plates, it should give pretty steady values assuming good contact with the foam on both sides. If the contact between the foam and plates isn't very good that might cause a little jumping when it's just sitting there, but I expect it would steady out if pressed and be proportional to pressure from then on. Sorry I couldn't be more helpful.
I had good contact between croc clips, multimeter and aluminium.
I had very good contact between aluminium and foam.
I also had moderate pressure in the foam at all times due to my cable ties (see attached picture).
I just wonder if there are different grades of conductive foam. It is very strange, don't you think!
In Belgium, anti-static foam is apparently harder to find. I had some that had a silver shine to it and came wrapped around an usb pci card, but sadly it didn't conduct any electricity (how strange is that?).
Then found some active carbon foam on ebay (used in kitchen hoods), which comes in large black sheets. I soldered electrical wires to 2 pieces of 5 eurocents, put some carbon foam between them and sandwiched that between 2 squares of duct tape. Really sturdy and worked fine on my Arduino. Needs quite a bit of pressure (fingerwise), but you can always press on the edges, they're more sensitive there. Use it to modulate music parameters in Pure Data, Fruity Loops, etc... via Arduino (patch available in Pure Data). And when no pressure is applied, it doesn't conduct (although that might not be the case with large (A4 size) surfaces, I've recently discovered).
I'm thinking of making a Really Big Pessure Sensor (2 x 2 meters), hook it up to the Arduino and jump around on it, possibly combined with a homemade graphite paint to make it position sensitive, but that another story. Feel free to steal the idea and help me over the obstacles.
The reasoning was that this would form 4 variable voltage dividers: when pressure was applied to the aluminum foil and foam underneeth, a current would flow from the +5V aluminum foil through a variable lenght of the graphite paint, through the fixed resistor and to ground. The voltage messured over the fixed resistors would vary in function of the position of the pressure point. But messured values didn't make much sense, maybe because the paint was not homogeneous enough? Maybe the values of the fixed resistors were too low and drained the hell out of the voltage source (thus dropping it's voltage).
Anyway, I did something similar with only one axis on a strip of paper that was darkened to saturation with a pencil (took me half an hour of scribbling) and it worked well as a ribbon controller. I'd suggest you start scribbling on a small square of paper and go from there. Keep me updated on tas_wouter@hotmail.com.
What could work is the same setup with four electrodes in the four corners of our resistant paint sheet, attached to their respective resistor. Shame on me...
Some has got time to test this?
http://www.elexp.com/ant_2asf.htm
at $0.90 per 4" x 5" piece, how can you go wrong?
As you suggest, the errors decline with force.
Bend, crunch, snap, stretch, much better.
"Hulk Smash!!" not "Hulk Longitudinally compress!"
"Hulk will now attempt to exceed durability of the structural envelope.!"
HAH
Great instructable !!!
http://www.instructables.com/id/DIY-Force-Sensitive-Resistor-FSR/
Neat to see you don't need the copper board though. Good idea sealing it.
I'd bet it'd be even easier if you put two plates on either side to squash it. (ie foam sandwiched by two copper plates, with wires soldered to it. )