Problems with capacity-based touchpads

[Reinhard Ruppelt]

Hello,
I am a bilateral amputee using two artificial limbs (myo-electric controlled hand prostheses) covered with PVC-gloves. With these hands it is not possible for me to use capacity-based touchpads /-screens (like the ones used with many laptops) because those kinds of touchpads can't be controlled by the artificial fingers. Do you know any work-around for input? My idea is to find a special purpose (electrical?) pen which allows input instead of using fingers. I didn't succeed yet.
Thank you very much in advance for support.
R.

[Dale Herzog]

Hi,

Here are a couple different solutions for you.

1. The first and easiest solution is to buy a bit of conductive thread and have a couple loops sewn into the pad of
whatever fingers you would like to use on touch screens.
a. This process has been discussed around the web for those wearing gloves and the fix would work for you as
well: http://www.crunchgear.com/2009/11/25/winter-is-coming-modify-your-g...
b. Small amounts of conductive thread (10 ft.) can be bought from lots of DIY electronics shops like Sparkfun.com
(note there are lots of other suppliers, but all I found are just reselling the Sparkfun spool.
i. http://www.sparkfun.com/commerce/product_info.php?products_id=9384
c. Disadvantage:
i. Creates puncture point in glove through which electricity and possibly water may flow.

2. A second solution would be to buy a bottle of liquid tool handle coating plastic, mix it with a conductive powder,
and paint a little bit onto the tips of the PVC glove.
a. Both the handle coating plastic and a conductive powder (like graphite) can be found at your average hardware
store.
b. This solution also has the advantage of
i. Keeping the glove unpunctured.
ii. Preserves whatever electrically isolative property the glove provides to the underlying components.
iii. Easier to dye to match skin tone.

c. Disadvantages:
i. Most of the coatings you will find (i.e. trade name “Plasti Dip: http://www.plastidip.com/”) I believe are vinyl not
PVC so you may want to do a test with an old glove.
1. Check for:
a. Adhesion of the conductive coating to the finger when the finger tip is flexed.
b. Change to the underlying PVC finger. and that coating the glove does not cause the PVC base finger tip to
become brittle.

3. Contact the manufacturer of the PVC glove and have them send you a sample of the glove resin and try the second method using it instead. I would guess that the glove manufacturer purchases the PVC from another company, so if you can find that name, you should be able to reach a person who will be able to give you a better idea of what to do

4. Find a robot geek. (I.E. Me.) I’m a robotics student with some background in working with polymers so feel free to drop me an email any time.

Cheers,
Dale

[Reinhard Ruppelt]

Hi Dale,
thank you very much for your detailed message.
As I have unsuccessfully tried various solutions I think that there is an unintended improper assumption in your proposed solutions.
I suppose the reason is that in my case there is a relatively big distance of isolated material (prosthesis) between the conductive touching material and the skin of my arm stump skin.
If you try your solution with your (normal) hand there is a sufficiently short distance between your skin and the conductive material so that your solution works.
I tried some settings with different conductive materials but couldn't move the curser. Can you verify your solution using absolutely isolating material between your hand and the conductive part?
Otherwise, what explanation do you have?
Cheers,
Reinhard

[Dale Herzog]

Ahhh. Ok, I've got a few ideas, but I'm going to have to chew on this one for a bit. Is there a non-identifying model number for the prostheses that you might be able to post so I can get a better idea of what the structure under the glove looks like?

Cheers,
Dale

[Reinhard Ruppelt]

Hi Dale,
thanks again for your effort.
In parallel I addressed my inquiry to Cirque Corporation Technical Support still awaiting their recommendations.
I use 2 myo-electrical prostheses from Otto Bock. They have two gloves: One inner glove protecting the mechanics/electronic components and one outer glove which serves for cosmetic purposes. I guess all in all this builds a highly isolating barrier.
Cheers, R.

[Dale Herzog]

Hey Reinhard,
I got back to thinking about this issue and I was wondering if you had ever thought of trying a circuit with a watch battery hooked up to a coil of wire (basically an inductor). You will probably have to add a resistor to adjust the power flow (or a contact switch to run at full power when you touch something flat,) but with enough juice I think that circuit would allow for the capacitive coupling that I understand the capacitive touch screens to work off of.

The nice thing is that you can make the inductor out of thin wire and a soft core so that it can be stored between the two glove layers and act as a flexible circuit. You might have a bump around the watch battery but, assuming the cosmetic glove isn't to thick, I think this would do the trick.

I suppose the catch is that I don't know how much transfer the human body produces nor how much resistance the outer glove provides. I suppose the thing to would be to wrap an inductor in the glove and hook it up to a power supply and see how much juice it takes to get through to a touch pad. (Sorry, I don’t have the gear for that part.)

References:
http://en.wikipedia.org/wiki/Touchpad
http://en.wikipedia.org/wiki/Capacitive_sensing
http://en.wikipedia.org/wiki/Capacitive_coupling

[Reinhard Ruppelt]

Hi Dale,
first, I'd like to thank you very much for your insistent efforts!
Yes, I think I agree, your proposal (inductor) could work. But all I need is a pen-like implementation. Self-integration into the glove doesn't make much sense as I have to replace them very often. And I need the functionality only from time to time. (Actually Bock Industries should enhance their gloves...)
Let me see if I can find someone to build such a small device. I'll let you know.
Thanks also for the references. They are helpful. (I looked only for german wiki sides and couldn't find much information).
Best regards, Reinhard (Berlin)

[Wolf Schweitzer]

http://www.freepatentsonline.com/y2004/0164065.html

I have no idea who builds that. But you are legally entitled to using the instructions of that patent as long as you just use the result for yourself and don't sell it as far as I have understood patent law.


Other than that, I wear self-made gloves on Otto Bock hands and not just 'cosmetic looking' ones, so it would be a possibility to make your own glove, maybe based on a similar strategy:

http://www.swisswuff.ch/tech/?p=224


Did you contact HP or Dell already? They sell machines like that, I'd assume they may have an idea.

Regards, Wolf.

[Reinhard Ruppelt]

Hello Wolf,
thank you very much for your hints.
At first glance it seemed you had found the solution I was looking for. When I took a closer look at the patent I found in principle the same device structure as in the embodiments I have evaluated (something conductive with a flat surface at least 8 mm wide that makes contact with the touchpad, a stick with a metal tip). The major difference is the heating element. Don't know for what use the heating is intended.
It seems that the inventor didn't let evaluate his solution by an amputee with artificial limb (myo-electric controlled hand prostheses) covered with PVC-gloves.
Best regards,
Reinhard
PS
I addressed an inquiry to the technical support of Cirque Corporation, a manufacturer of touchpads, still awaiting their recommendations.

[Jon Kuniholm]

There's an instructable that discusses the conductive thread option in detail here.

Jon

[Reinhard Ruppelt]

Thanks, Jon.
The problem with such a solution is that it requires a human hand inside the glove...
Reinhard

[Nick Hockings]

Hi Reinhard,
I just came across your question, so you may already have found a solution. I did a few experiments, and found a solution that seems simple and practical.

I tried putting small coins on the touchpad and pushing them around with a pencil. The smallest one (Argentine 5 Pesos) is about 10mm in diameter and works fairly well at moving the cursor around. Larger ones tend to be interpreted as a two finger touch - which means scroll on my macbook.

What seems to be needed is a flat conductive surface of the right area to form a capacitor plate. A final fix could be a pen/pencil with a lump of wax on the end shaped to provide two flat faces (single finger and double finger touch) and covered in foil.

You could of course have the whole thing cast in alloy for durability once you have the ideal shape.

I hope this helps,
Nick

[Reinhard Ruppelt]

Hi Nick,
thank you very much for your support.
No, I haven't found yet a solution that works for all the diverse capacitive based input devices (notbook touchpads, smartphones and the spreading ATMs for all kinds of purposes.
Even the smartphone pencils are specific to the corresponding product and generally do not work with ATM input screens and laptop touchpads for example.
But, I'll try coins in the way you described. It would be a practical work around standing in front of an ATM and misusing the nose...
Cheers, Reinhard