Graphite Touch Button: High Conductivity & Faster Response

[hackhard]

graphite has high conductivity , so i though of making a touch button out of a pencil drawn pattern on the wall.the pattern is shown below.
when not touched -resistance between ends of the pattern >200Mohm (exceeds dmm limit)
when fully pressed - resistance between ends of the pattern = 1.3 Mohm.
but Vout rises after delay or falls after delay of some 100 ms.due to high impedance
this pattern connects skin resistances in parallel
can someone suggest a better pattern ( of lower end to end resistance) ?
for faster response

 

[NascentOxygen]

Hi hackhard. You probably have the transistor drawn incorrectly on your schematic.

I like your experimental bent, but a problem with a graphite pattern is that it will sooner or later probably smudge and establish a bridge between the tracks.

In future please keep images to under about 1000 pixels across, otherwise the thread gets displayed in tiny sized print to accommodate the oversized image on our screen.

 

[Nidum]

Search : ' electroconductive ink pens '

 

[hackhard]

Search : ' electroconductive ink pens '

its very costly
mine is a cheaper solution

 

[davenn]

its very costly
mine is a cheaper solution

.
but not reliable ... cheapness come with disadvantages as @NascentOxygen said

 

[anorlunda]

Here is a very different approach to do what you are doing. Perhaps you could have fun with a project to do that.

Jonathan Coleman's research group at Trinity College Dublin discovered that Silly Putty "becomes an incredibly sensitive strain detector that can track blood pressure, heart rate, and even a spider's footsteps" when mixed with graphene.

Popular Science reports:That graduate student, Connor Boland -- who has since earned his doctorate -- made a batch of graphene in water and added the Silly Putty polymer. As he mixed them, the graphene sheets stuck to the polymer, creating a black goo the researchers dubbed "g-putty." When they ran an electrical current through the g-putty -- graphene-infused polymers can conduct electricity -- they discovered an extraordinary sensitivity. "If you touch it even with the slightest pressure or deformation, the electrical resistance will change significantly," Coleman says. "Even if you stretch or compress the Silly Putty by one percent of its normal size, the electrical resistance will change by a factor of five. And that's a huge change." That change makes g-putty about 500 times more sensitive than other deformation-detecting materials, which would respond to a similar compression with a mere one-percent change in electrical resistance. The results were published in the journal Science.

Graphene has been made with pencil lines and scotch tape. https://en.wikipedia.org/wiki/Graphene#History

 

[hackhard]

thanks for help. I've decided to use conductive ink

 

[hackhard]

conducting paint is too expensive.
are there any other alternatives to copper foil strips or Bare conducting paint

 

[hackhard]

i found this
http://www.ebay.com/bhp/copper-tape ebay

 

[BrockLee]

If you want resolution try making a lense to spread out a cheap dollar store solid state laser onto a inner reflective box frame and lining the inside parameter with a grid of cut mirror reflector's each precisely cut at width and angle's prime to each other and spaced at exact intervals, with incident angles toward two or more LDR(light dependent resistors) and coordinates of blocked pulse's like finger tips can be extracted easily though any serial adc.

 

[jim hardy]

Try increasing R2 to 220K and pulldown to 10 meg ?