Looking for Proximity/Touch Sensor Components that works through fabric

Hi folks!

This is my first post here, and english is not my native tongue; so I'll try to keep it short and concise. :)

I spend some of my spare time working on cosplay/semi-professional costumes, and develop applications for a living - so I do have a rough understanding of electronics, but I'm still pretty much a rookie when it comes to the basics.

Currently I'm working on a costume which will have various LEDs embedded into it, like color-changing ones in the eyes, and additional ones for certain markings. Installing and controlling those with an Arduino is all peachy - but I'd like to go a step further, and allow the wearer to control/interact with the program.

What I'd like to do is use the gloves of the costume and have a way to detect if (and which) of the 4 fingers is pressed against the palm (or thumb would work too!), so that I can respond to this programatically.

Attaching conductive plates to the fingertips and to the thumb/palm would be the easiest way... but that'd be fairly ugly, so I'm looking for a smarter way to do it.

If I were to pull 5 wires to the glove, have one go to the thumb/palm, one to each fingertip, are there any components I could use to figure out which one (or, and that'd be the most awesome case - which ONES) close(s) the "circuit"? Components should be as small & flat as possible, and must work despite being hidden under the cloth/material of the glove - which could be up to 2-3mm of fabric.

If you need further info, let me know; and thank you in advance for any replies and nudges in the right direction.

Regards,

~Luchs

Any capacitive system will work through fabric unless the fabric is actually conductive.

You can sandwich a conductive fabric under the palm, with another insulating layer of fabric underneath this against the skin, then have just wire woven through the fingers.

Each wire is driven with a pulse sequence from the Arduino and the palm pad will pick it up (may need some amplification with an op-amp) when a wire comes close. As the Arduino generates the pulses, it will determine which wire (or combination) it was.

Note - the Arduino must be in the cuff of the glove so the wires are short, and you will need some grounded shielding (like coaxial cable) on the wires between the Arduino and the fingers and palm, as well as a degree of grounding of the Arduino to the hand itself (with more conductive fabric).

Wow - thank you for that swift response! I think I can follow the concept, but I’m not entirely sure I could pull that off.

The smaller issue I see, besides that I’d have to spend some time reading myself into it, would be the proper isolation & grounding. Such costumes usually aren’t very light, and after wearing it for 2 hours the inner glove will be soaking wet already, which would make pretty much everything conductive there.

The bigger issue I see however would be this:

Paul__B:
Note - the Arduino must be in the cuff of the glove so the wires are short, and you will need some grounded shielding (like coaxial cable) on the wires between the Arduino and the fingers and palm, as well as a degree of grounding of the Arduino to the hand itself (with more conductive fabric).

I simply don’t think that’s feasible. I can easily run a cable along the arm and have small components on the palm or at the fingertips, but I couldn’t fit an Arduino board there, as the base of this is skin-tight, elastic fabric.

I did spend some further time thinking about it; and another solution (not perfect, but probably easy and cheap to implement) could be small using tip switches (like those) in the finger tips, and a pressure pad (like this) on the palm. Of course it’s not a 100% clean approach, as this would also fire if you’d firmly grasp something, but I think it’d be very easy for readout.

~Luchs

There's conductive and there's conductive. A sweat-soaked fabric is not conductive enough to upset a capacative sensor.

I would think that a row of switches just under the first layer of fabric in the palm will be sufficient. The row should not be straight because your fingertips don't make a straight line.

What about using a conductive paste?

MorganS:
There’s conductive and there’s conductive. A sweat-soaked fabric is not conductive enough to upset a capacative sensor.

I would think that a row of switches just under the first layer of fabric in the palm will be sufficient. The row should not be straight because your fingertips don’t make a straight line.

That’d be another option, yes; I do like the pressure pad on the palm, tho, so that there won’t be any presses registered just by resting your hand somewhere or grabbing something lightly. Having the switch only register when the pressure on the palm is also present will make this a bit more stable, imho.

HazardsMind:
What about using a conductive paste?

I’m not entirely sure where that would get applied. This is a fantasy themed costume, the ‘gloves’ will have both fake fur and fake leather pads on palm and finger tips; it’s essential that the solution must be completely invisible.

If you’re recommending to apply conductive paste to the pads on palm/fingertips - I’m not sure how well that’d play. There’s a lot of motion in that fabric when it’s being worn; anything that coats those surfaces would break or be ‘worn off’ after a short amount of time.

Have a look through the SparkFun flex/force sensor range

I think the following options might help:

  • Flex sensor on the back of the glove fingers - sense when a finger is bent
  • Force sensitive resistor in the fingertip to sense when a fingertip is pressing something
  • Membrane potentiometer in the palm to sense when there's pressure on the palm - can also be used to sense where the pressure is along the length of the membrane.

Combine any two of the above and you might have a solution.

Luchs: I simply don't think that's feasible. I can easily run a cable along the arm and have small components on the palm or at the fingertips, but I couldn't fit an Arduino board there, as the base of this is skin-tight, elastic fabric.

I sure hope you don't think an "Arduino" means a UNO.

Have you seen this?

Or perhaps this?