MSP430FR2512: Touch through metal with brass possible?

Hello Jesse,

Yes.  Brass is a conductive metal so it will work the same as other common materials used for metal touch, such as stainless steel, aluminum, etc.

For programming and debugging the MSP430FR2512, the CAPT-PGMR is recommended.  It's around $20.  You can use other programmers but you won't be able to communicate with the CapTIvate Design Center which is used for generating your starter project and tuning your sensors.

Does this answer your question?

Yes, that answers my question. Thank you.

If I want to design the spacer into the PCB like in figure 17 of http://www.ti.com/lit/an/slaa811a/slaa811a.pdf

What do I have to say to my PCB manufacturer? If I tell them to 'grow the prepreg' like mentioned in the PDF, would they understand? Is there a better way to specify it?

Hi Jesse,

I would recommend reaching out to the PCB manufacturer on how to specify this, but basically yes, you are essentially asking for an additional laminated layer on the electrode layer.  Keep in mind you also need an adhesive between the PCB and metal overlay.  Do not use double sided bonding tape like 3M 486/487 as these will not form a rigid bond.

The method we use to assemble our metal touch demo board uses a thin thermal bonding film, such as a 3M 583, to form the spacer and bond the two pieces together.  The idea here is you need a very solid bond between the PCB and the metal overlay to prevent any movement when pressing on the metal, so the thermal bonding film provides the adhesive as well as the spacing.  The film is 2mil (.05mm) thick and when cured it is rigid (won't compress or move).  Note this method does require heat and pressure to ensure the appropriate bonding, so it's not a simple process to do in manufacturing.

What would be the preferred way to make the cut-outs in the film? Lasercutting?

Is adhesive still necessary if the PCB is bolted to the metal overlay in multiple places?

Also:

Would it be possible to use the EVM430-CAPMINI to evaluate this application?

So I would try to apply the film and brass front to the EVM, reprogram the MCU and get an idea of how it works.

Hi Jesse,

Regarding making the cut-outs in the film, yes, that is probably the preferred method for mass production.  The vendor that builds our CAPT-METAL demo panel uses a die cutter, but the quantities are only a few hundred and they already use the die cutter for other things they build.

Interesting thought about using the EVM430-CAPMINI.  However, if you mean to cover all the buttons with one large piece of brass, that won't work.  You need to remember that when you press on the brass over one button, the brass should not move over any other button.  Else all the buttons will go into detect.  This is the reason for the spacer - to hold the metal flat and only allow the metal to bend in the region of the spacer with a hole directly over the electrode.  And if you are referring to using the 3M 583 film, you will need some way to apply pressure and heat to active the adhesive properties and cause it to cure solid.  Doing so would warp the EVM430-CAPMINI plastic overlay.  And also, don't forget the brass needs to be grounded as well.

I know this sounds like it is difficult, and it is.  We have worked with several customers who originally wanted metal touch but they realized the effort and changed their mind. That's why there aren't more products that use metal touch.

BTW, what is your application?  Why do you want to use metal?

Hi Dennis,

Apologies for the radio silence.

The customer wants to have a brass panel as input for a retro-look audio system.

Most of my questions are answered, I think I can figure out the rest by reading datasheets.

Thanks