Capacitive Switches

[Winsu]

Hi All,

I would like to use a capacitive switch for an application. The reason is that we don't want to make any holes on the housing for IP reasons but we need a switch for a specific feature. I have though about capacitive switches and if they could still work behind a metallic plank. The idea is that the capacitive switch is touching the housing from inside and the user can touch the area with his finger from outside the housing where the capacitive switch. Would that trigger the switch even though there is a layer of metal between the user and the capacitive switch?

Anyone has done something similar or have any experience on this?

Thanks in Advance,
Winsu.

 

[KlausST]

Hi,

It can´t work if the metal is one sheet.
It may be possible if you have many small metal pieces. But I guess this is not what you want.

Metal "shields" the AC electric field, so it can´t reach your finger.

Klaus

 

[FvM]

A piezo switch might work.

 

[BradtheRad]

Build a microphone circuit that detects your finger tapping on the enclosure. Consider making it respond to two quick taps (similar to the commercial product 'Smart Clapper').

Or if the metal rings at a certain frequency, then make your microphone circuit respond to that frequency.

 

[KlausST]

Hi,

What IP level do you need? What are other requiremens?

I think about a membrane keypad with the flexible connector going underneath the keypad into the case, so it's sealed by surrounding adhesive.

Klaus

 

[Winsu]

Hi Klaus,

Actually the IP is not the main reason. The main reason is that they don't want to make holes to not to increase the price of the housing. Therefore the solution has to be cheaper than the increase in cost when making a hole in a housing.

 

[KlausST]

Hi,

we don't want to make any holes on the housing for IP reasons

I just took your words seriously...

Now it´s "cost".
There are several ways to "put holes in a housing". Milling/drilling is one solution but surely for high volume there may be more economic solutions. But I guess you don´t want to talk about this.

So I just can say: in usual case a "metal layer" will kill your idea about capacitive switches. Maybe you have a special case, we don´t know. Or you have to use a different technique.
Acoustic, magnet, optic, ... ... (while "magetic" may not work with bare fingers)

Klaus

 

[Winsu]

Hi,

I just took your words seriously...

Now it´s "cost".
There are several ways to "put holes in a housing". Milling/drilling is one solution but surely for high volume there may be more economic solutions. But I guess you don´t want to talk about this.

So I just can say: in usual case a "metal layer" will kill your idea about capacitive switches. Maybe you have a special case, we don´t know. Or you have to use a different technique.
Acoustic, magnet, optic, ... ... (while "magetic" may not work with bare fingers)

Klaus

Hi Klaus, there is another product that is identical but hasn't got a switch ( the switch is to prove that a certain functionality works). The reason is that we would like to use the same housing for both products ( with switch and without switch ). If the new way to fit use without making holes is more expensive than making a hole it is not cost effective, therefore it would be better to make a hole.

If the metal sheet stops the AC field I dont think we can find any other cheap solution. Thinking on other solution like microphone would be more expensive than making the hole.

 

[mtwieg]

If there has to be a continuous sheet over the button, then another option is to use an inductance switch. See concept below. TI makes a bunch of chips for this purpose. One important thing to keep in mind is that it depends on deformation in the metal panel, so you have to be careful with mechanical design. Otherwise you can register false presses when you squeeze or shock the enclosure in other places.