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I have two terminals which I will measure resistivity between. I will be manually touching the terminal pair to different value resistors.

The terminal pair might look something like a 9v battery plug: enter image description here

I don't want to be precise about where I touch the resistor (lining up the terminals with the resistor wires).

Is there some kind of "pad resistor" (the size of a small coin) in which I can just touch two terminals anywhere on the surface and have the same effect as if i were using set resistors?

Note: the reason I am using resistors is so I can have a series of pads with unique signature based on resistance over the terminals. If there is some other solution in which I can have unique "pads" be recognised by a microcontroller as different without using resistors, this will work also.

Thanks!

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    \$\begingroup\$ it is difficult to visualize what you are talking about .... please post a picture \$\endgroup\$ – jsotola Jan 28 at 3:48
  • \$\begingroup\$ oops, i failed to realize that you are the OP that asked about the thumb contacts on your previous post \$\endgroup\$ – jsotola Jan 28 at 4:08
  • \$\begingroup\$ Haha you are uniquely positioned to answer then. Thanks again for the other post. \$\endgroup\$ – SirPattalot Jan 28 at 4:51
  • \$\begingroup\$ here is something similar ... maestroglove.com \$\endgroup\$ – jsotola Jan 28 at 5:02
  • \$\begingroup\$ Ahh I’ve seen similar products. I’m not a fan of the whole glove design. I’m playing around with alternatives. Thanks though! \$\endgroup\$ – SirPattalot Jan 28 at 5:12
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different conductive materials have a different bulk resistivity. so you could use them in this. eg get thimbles mage from or coated with conductive rubber in 4 different formulations (or the same formulation in different thicknesses) but the readings you get will to some extent be pressure dependent.

a better solution is probably to instead make a pad with many terminals that are all fed to a single resistor via a diode network, that way even if each of the contacts bridges multipler terminals you can still read the single resistor

schematic

simulate this circuit – Schematic created using CircuitLab

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  • \$\begingroup\$ Assuming four of these thimbles, do you think the formulations or thicknesses could be so that there is no overlap between their resistive value range, regardless of pressure variation? \$\endgroup\$ – SirPattalot Jan 28 at 4:49
  • \$\begingroup\$ probably not... see my second suggestion. \$\endgroup\$ – Jasen Jan 28 at 5:02
  • \$\begingroup\$ Interesting idea! As I mentioned I’m a bit inexperienced with circuits. Is there anything off the shelf that would match this criteria? And if not, do you think such a design could be implemented on a 10x10mm medium? \$\endgroup\$ – SirPattalot Jan 28 at 5:06
  • \$\begingroup\$ Also back to the first solution, could I use completely different materials? Rubber, wood, copper, etc. would these work and have resistive differences big enough to avoid overlap? \$\endgroup\$ – SirPattalot Jan 28 at 6:15
  • \$\begingroup\$ rubber and wood will look similar to air electrically, all metals will looks similar. so no. probably won't work. \$\endgroup\$ – Jasen Jan 28 at 7:54
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Alternative solution:

Use RFID keyfobs (example) and your reader is an RFID reader. You might be able to adjust the reader's signal strength so that it won't read the fob until the fob is actually touching the reader. (or just put something in front of it to weaken the signal)

If these are too big for you, you may be able to crack open the plastic, re-arrange the coil into a smaller coil, and mold them into your own plastic.

Each keyfob has a unique ID number which the reader can see.

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Alternative solution:

Find a material with a measurable resistance in-between "none" and "lots". (i.e. not a conductor, not an insulator either). A grid of pencil lines on paper might work for a prototype.

Make a pad of this material. Measure the resistance you get, with the terminals in different positions and with different amounts of pressure.

See if you can make several different pads, with different amounts of conductive material, so the resistances don't overlap. Maybe different pencils, or different metal sheets (if you can measure low resistances), or different metal mesh, or something like graphite (in different thicknesses).

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  • \$\begingroup\$ Great solution! I will try this and see how it compares to the solution I'm currently employing. You've been a great help \$\endgroup\$ – SirPattalot Mar 6 at 12:21

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