This is totally random question, but for my arduino project i am hoping to measure linear displacement and record the voltage reading. I was thinking of using a linear potentiometer, the only problem is finding one that is long enough (i need it to travel about 5 or 6" ). Does anyone know where i can find one that long, or if there is any other component that could work?
Cheers
You might have to "gear down" the linear motion output in some manner (perhaps using a compound lever mechanism) in order to use a regular linear potentiometer.
Another option would be to use a multi-turn potentiometer (again, possibly with a gear down).
If you have the room, a regular potentiometer could be hooked to the linear travel part via a long lever, so that the travel causes the lever to move in a small arc.
You could also possibly measure distance using something like a Sharp IR sensor, or something like a Ping (ultrasonic) sensor.
A complex method might be to use a long linear CCD (like in a scanner), and measure the position of a light or a slit as it travels along it (by clocking the data out from the CCD and finding which element in the CCD is sensing the light/slit).
You could attach a linear gradient pattern to the linear portion, progressing from light to dark (or clear to opaque); such a pattern could be printed on a laser printer onto transparency plastic, or onto paper like for PCB etching and transfered via heat. Use a photodetector and light source of some kind to sense the level of light being reflected/transmitted by the pattern.
Similarly, you could print a binary pattern in a linear fashion and do the same thing with an appropriate sensor; look up "shaft encoders" to understand the idea; except instead of a "round" encoder, your encoder would be printed linearly. Note that depending on the precision needed (steps between measurements), your encoder may need a lot of bits (past about 10 bits, it is difficult to homebrew such an encoder - 10 bits would give you about 0.006 inches per step, though, over 6 inches of travel).
I don't know what your budget is but in the industrial automation world there are devices called "string potentiometers". For example:
You pull on a string and they tell you how far you've pulled. Not cheap, but is plug-and-play (or plug-and-pull?)
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RuggedCircuits >> That is perfect, exactly what i was looking for. Thanks everyone!
crosh: I was thinking of doing the same thing, only thing by using the levers i will lose some resolution, which is pretty important in this particular application.
I don't know what your budget is but in the industrial automation world there are devices called "string potentiometers".
Interesting, but they don't look like anything more than a retractable cord reel attached to a multi-turn potentiometer (perhaps with some extra-gearing on the long travel versions); you could probably homebrew one using a surplus multi-turn pot and a retractable keychain mechanism...
Perhaps mate one of these:
http://www.allelectronics.com/make-a-store/item/TRC-2/RETRACTABLE-CABLE-REEL/1.html
...with one of these:
http://www.allelectronics.com/make-a-store/item/RTP-200/200-OHM-MULTI-TURN-TRIM-POTENTIOMETER/1.html
;D
If one needs to go inexpensive for ~6" of travel, a "string potentiometer" could be from the plastic lid of a 32 oz citrucil jar (~4.5" dia.), a standard Radio Shack pot, and some other simple materials.
You might want to try to modify a Digital Calipers. Most of the have a serial digital output.
Check this out:
http://www.nerdkits.com/videos/digital_calipers_dro/
Arduino from the UK
www.skpang.co.uk/catalog
These will be spendy as they are industrial applications...
ETI Systems http://www.mouser.com/Search/Refine.aspx?Keyword=eti+systems+precision+linear