I need a to build a sensor which should be a 30cm plate used to detect location of metal piece I will be dragging on its surface.
I know I could build it with graphite but this thing should be something robust.
Plate should be 30x3cm and I will hand-drag 1cm metal stick over it and I expect detecting value of location on analog pin.
Any suggestions?
You could wind some varnished wire around a flat torus. Creating a ring doughnut kind of affair. Glue it down (or possibly embed in epoxy to barely cover it. Then sand down the surface to expose the bare wire, but not so much as to short out individual turns. Put a connection to your wand and use it as a conventional potentiometer.
the piece is heavy? or can scratch the surface? perhaps a resistive touch panel can do the job with a good protection film over it.
If it not fit the other solution can be edge infrared crossing matrix solution but it's more complex and after you have image recognition with camera.
what is the position precision you need?
Thank you both for replies!
@Genesis92 Yes, it is heavy and should be able to withstand a lot of wear and tear. I am hoping I can place strips of that on wall or floor so it should be thin. Position precision at least 20 levels but the higher the better.
@KenF since it has to be rather flat the winding flat torus might not be ideal. It also would not stand enough use before wire is worn.
I don't know if I could find large and cheap graphite plates and if these would act same as "pencil resistors" on the paper. Any experience with those?
They'd also be softer than copper
What resolution do you want? Would a set of discrete steps (such as from 0.1" stripboard)
be plausible for this? Discrete resistors between each trace...
Hmm, @MarkT that is pretty good idea! I will keep it as backup.
What do you guys think about sheet of carbon fiber. I don't have anything made of it to test but I was hoping that would have desired electrical properties and also be extremely durable?
Some of these are comparable in size, they are very rugged and actually work on the same principle.
Adjustable Wirewound Vitreous Resistors
EDIT:
You could remove the adjuster clamp, then on end of your metal piece attach a carbon brush like is used on variac or powerstat controls.
dlloyd:
Some of these are comparable in size, they are very rugged and actually work on the same principle.Adjustable Wirewound Vitreous Resistors
EDIT:
You could remove the adjuster clamp, then on end of your metal piece attach a carbon brush like is used on variac or powerstat controls.
This is exactly what I had in mind. BUT you could just build your own using some stout resistance wire. and make it flat and round 
If you get a conventional joystick control for a model aircraft it contains a couple of pots operated by a single actuator. One pot measures the x axis position and the other the y axis position. You connect the pots to a pair of analogue inputs on the arduino and then compute the position on the plate from the two inputs.
Whilst movement is possibly restricted to about +- 2cm in all directions, you could rig up some form of gear or lever reduction system so that movement over your 30cm range equates to the movement of the joystick.
The sensor wand or whatever then moves the joystock via the lever reduction system.
Another approach would be to use a digital scale yanked out of a pair of chinese-made digital calipers (surprisingly cheap). These will be way more accurate.
For a bunch more information, Google for: chinese caliper scale arduino
Hi, what you are looking for is a linear position sensor am I right?
What is the application, can you post a picture of what you want to monitor the position of.
What does the metal stick draging over the metal plate do?
Does it need to be conductive?
Tom......
Yes, linear position sensor which will be used as part of sound installation where visitors will be able to play sounds with different metallic objects.
I will need several of these outputting raw values to PC.
I think it needs to be conductive. So far I am thinking most about carbon fiber as it should have a lot of resistance or I will go around home depot and hobby shops with ohmmeter testing resistance of everything I see. I have just read that many polymers are conductive so maybe I could find something there.
@DrAzzy I thougt calipers have sensor similar in computer mouse and you need to reset it at 0, but visitor should be able to place object anywhere on sensor instead of dragging it
Conductive Plastics
http://www.boedeker.com/esdmatls.htm
Semiconductive Coatings
http://staha.vtt.fi/stahayhdistys/atex%20tr/Semiconductive-conductive.pdf
Semiconductive Tape
http://multimedia.3m.com/mws/media/41134O/scotch-13-electrical-semi-conducting-tape.pdf
yes it's a good option too Dlloyd with good soft wiper
jakovn:
Yes, linear position sensor which will be used as part of sound installation where visitors will be able to play sounds with different metallic objects.
Sounds like you want a fairly standard capacitive touch screen assembly.
If you were using direct contact, the objects would need (as indeed they would anyway in a public setting) to be tethered. With a capacitive touch screen, different objects could be sensed by a digital code sent to the respective tethers.
Thank you all! I have now good starting point with a few of these things to try