Touch Pad on Laptop - Make Me Smart

Wes Bucey

Quite Involved in Discussions
#1
So, today I was working with a drawing program and I had [what I thought was] a flash of inspiration:
Why not use a plastic stylus on my touch pad for finer control of the drawing line?

Some of you, of course, are already sneering at my naivete.

I was stunned to discover the cursor wouldn't move when I used the pointy stylus. Then I tried a blunter tool, thinking maybe more sensors on the pad had to be involved - still no cursor movement. then, I thought, "AHA! It has something to do with electrical ground." So I tried a rounded copper rod - still no cursor movement, but it works fine with my finger or my finger nail (finer edge than the stylus!)

So, geniuses of the modern world, please explain to a decrepit senior citizen what I'm not grasping - why does my finger or finger nail move the stylus, but an extension (plastic, wood, or metal) does not.
 
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Mikishots

Trusted Information Resource
#2
So, today I was working with a drawing program and I had [what I thought was] a flash of inspiration:
Why not use a plastic stylus on my touch pad for finer control of the drawing line?

Some of you, of course, are already sneering at my naivete.

I was stunned to discover the cursor wouldn't move when I used the pointy stylus. Then I tried a blunter tool, thinking maybe more sensors on the pad had to be involved - still no cursor movement. then, I thought, "AHA! It has something to do with electrical ground." So I tried a rounded copper rod - still no cursor movement, but it works fine with my finger or my finger nail (finer edge than the stylus!)

So, geniuses of the modern world, please explain to a decrepit senior citizen what I'm not grasping - why does my finger or finger nail move the stylus, but an extension (plastic, wood, or metal) does not.
A touchpad is constructed using a grid of conductors (two layers separated by an insulator). The top layer has conductors running at right angles to the bottom layer. A high frequency signal is continuously applied to the touchpad and a capacitance appears at each intersection. When your finger touches the pad, that intersection location allows a charge to leave that intersection and the capacitance changes.

Touchpads are “tuned” in terms of capacitance to only allow objects of similar density to the human body to trigger.

Wanna know how touchpads detect a tap?:rolleyes:
 
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Wes Bucey

Quite Involved in Discussions
#4
A touchpad is constructed using a grid of conductors (two layers separated by an insulator). The top layer has conductors running at right angles to the bottom layer. A high frequency signal is continuously applied to the touchpad and a capacitance appears at each intersection. When your finger touches the pad, that intersection location allows a charge to leave that intersection and the capacitance changes.

Touchpads are “tuned” in terms of capacitance to only allow objects of similar density to the human body to trigger.

Wanna know how touchpads detect a tap?:rolleyes:
Ok, so I'll bite - what substitute for the "density" of my human body will work? Why does my fingernail work? I'm so confused!:confused:

Wanna know how touchpads detect a tap?
Sure!
 

Wes Bucey

Quite Involved in Discussions
#6
Look for a "Capacitive Stylus", they are available for a couple dollars on Amazon.
Serendipitously, I received an email ad today from the Cell Phone Shop (I've been happy with discount batteries and chargers from them), so I looked up "capacitive stylus" and found http://search.cellphoneshop.com/search?asug=ca&w=capacitive+stylus

Now there are too many choices!

So, after looking up a WIKI and a few other sources, I realize my instinct was more correct about electrical conductance than "density," but I'm still not clear on EXACTLY the difference between a "capacitive stylus" and a copper rod - is the copper rod too conductive? I put a sheet of dry paper over the pad and it still works with my finger; two sheets and it doesn't.

This little question will be a "mindworm" (a word I use similar to an "earworm" NOT the comic book character "Mindworm") for me until I completely understand it.
 

Mikishots

Trusted Information Resource
#7
Ok, so I'll bite - what substitute for the "density" of my human body will work? Why does my fingernail work? I'm so confused!:confused:

Wanna know how touchpads detect a tap?
Sure!
Your nail is closely enough attached to your finger that it can take on that density. That being said, it does not work for me, but it does for my son. No idea why, but it doesn't seem to be consistent from person to person.

A metal rod does not have the same dielectric difference that a human finger provides. It won't work on a capacitive pad, only on a resistive pad.

Taps are detected on pads that not only measure the location of a touch, but also the frequency. Pads that allow multitouch are able to simultaneously register more than one point at a time, and gestures are simply sensed by an algorithm that detects speed and adjacent intersection activations to determine the direction and rate of the gesture.
 
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