graphite touch button (pencil drawn)

Projects General Guidance
1

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 :slight_smile:

2

There should be no delay, because there is no capacitor in the circuit.

The transistor is powered the wrong way, so can't work.
And it should not drive a low impedance (220ohm) load.

The transistor is not even needed if you have a >100Megohm Cmos port available.

A circuit like that could work two ways.
Conduction from your finger and/or mains hum pickup from your finger.

Hum from mains wiring will be your enemy with a pencil drawing on the wall.

Who needs a circuit like this if you have >100Megohm Arduino inputs available.
Leo..

3

graphite has high conductivity

No it hasn't.
You would be much better off using copper foil strips or Bare conducting paint to do this.

The main problem with graphite is that it doesn't stick very well to a surface and cracks soon stop any conduction paths.

4

Grumpy_Mike:
No it hasn't.
You would be much better off using copper foil strips or Bare conducting paint to do this.

The main problem with graphite is that it doesn't stick very well to a surface and cracks soon stop any conduction paths.

5

I just said that :confused: no point in just quoting my post and not making a comment.

Given your other posts I think you might be better off actually learning some electronics then you could act as your own filter for "imaginative" ramblings.

6

thanks for help. ive decided to use conductive ink

7

Grumpy_Mike:
No it hasn't.
You would be much better off using copper foil strips or Bare conducting paint to do this.

The main problem with graphite is that it doesn't stick very well to a surface and cracks soon stop any conduction paths.

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

8

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

Kitchen type aluminum foil?

Paul

9

Hi
Have you googled rolls of self adhesive copper ebay

or without ebay.

Tom.... :slight_smile:

10

TomGeorge:
Hi
Have you googled rolls of self adhesive copper ebay

or without ebay.

Tom.... :slight_smile:

thanks ,thatll work
copper tape ebay
maybe Ill stick it on my tshirt to work as buttons for music player app

11

It might work better if you didn't have such a low resistance load in the transistor collector. Try 10k.

edit: the transistor is only getting a base current of a few uA . It'd have to have gain of >1000 to pull down the 220 to ground.

despite that I concur with other posters that graphite isn't a very good idea.

regards

Allan