capacitive touch sense switch

[philipe]

Hello, im working on a project in Eagle PCB and I decided to add capacitive touch switches to it. my only issue is I have no idea how to add custom capacitive touch sense switches. Does anyone here know how to do this? if so could you write me a easy to follow tutorial on how to do so?

 

[barry]

If they are CUSTOM switches, how would anyone besides you know ANYTHING about them???

 

[BradtheRad]

I have touched my finger to the input pin of transistors or logic gates, and then saw 60 cycle pulses at the output. My body picks up mains hum (from everywhere in the room), and carries it to the input.

When I remove my finger the pulses usually stop. However they may continue if a length of wire is attached to the input pin. The wire (or my body) is like an antenna picking up mains hum.

This isn't exactly capacitive sensing, and I doubt that touchpads operate on this principle. Nevertheless it's easy to experiment with.

A pullup/down resistor may be needed at the input to make operation reliable. Say 1 or 10 Mohm.

 

[KlausST]

Hi,

I really don't know what you are asking for.
PCB layout for touch sensors? What size? Round? Square?

Electronics? Semiconductors? ICs? Schematics?

Klaus

 

[d123]

Hi,

Not sure if this is what you mean (if not it might be of use to someone else in the future) :

How to Use Autodesk EAGLE to Design Custom Components

Creating Components in Eagle (Almost) Frustration-Free

Library Basics Part 3: Creating Your First Device in Autodesk EAGLE

Eagle Tutorial 4/4 – Creating new schematic symbols and custom footprints in EAGLE CAD

 

[betwixt]

This isn't exactly capacitive sensing, and I doubt that touchpads operate on this principle.

They don't normally work by sensing stray fields because it would fail on battery powered equipment or anywhere electrically quiet.

The principle is to use a small but constant current to charge the sense pad and see how long it takes to reach a threshold voltage. When it reaches it, the charge is changed to a discharge instead. Basically it works like an RC oscillator but with a fixed charge current of a few uA. Because the current is low the frequency of oscillation depends largely on the value 'seen' as the capacitor. A change of only a few pF will shift the frequency far enough for it to be detected. This allows the sense pad (the capacitor) to be well insulated for safety, for example being a pad on the reverse side of a PCB with the touch area on the front surface.

Brian.

 

[philipe]

Capacitive touch sense switch

Hi, this is a correction to an earlier thread post. I didn't give enough information as to what I needed help with hopefully this increases my chances of finding a resolution to my problem.

Im working on a project and decided that I would like to use capacitive touch sense switches instead of regular buttons. I'm using eagle and I have no idea how to create them from scratch I will need..

1 30mm x 18mm rectangle

4 28mm x 16mm rectangles

and..

16 32mm x 32mm squares

..for my capacitive touch sense switches. hopefully this helps. I was wondering if someone with experience could write me a brief and easy to understand tutorial on how to create capacitive touch sense switches with these measurements using eagle.

Thanks an advance,

Phil

 

[KlausST]

Hi,

How I would do it:

https://lmgtfy.com/?q=capacitive+sensor+design+guide

There are documents, examples, even videos....

Klaus