MSP430FR2632: Touch sensor IC suggestion

Hi Stephan,

The MSP430FR2632YQW (DSBGA) is perfect for this type of application.  It has 8 capacitive measurement channels and very impressive low power operation (typ 4-5uA) while still monitoring the on-head detection sensors and with the CPU completely in a low power state.  For proximity sensing, your 1.5cm is well within the 2-3cm possible with this device.

Don't forget to take a look at the Captivate Technology guide, and the Captivate Design Center GUI (free).  The Captivate Design Center makes it very simple to setup and configure your sensors, plus it generates 100% of the code needed to run all of your sensors.  You only need to add in the functionality for your application by using simple callback functions.  Here is a section in the Captivate Technology guide that shows you how to do this.

If you are looking for a starter kit or EVM to evaluate the MSP430FR2633 MCU, I would suggest the following:

https://www.ti.com/tool/CAPTIVATE-FR2633

CAPT-FR2633 MCU module

CAPT-PGMR programmer/debugger/HID serial communications bridge

CAPT-BSWP self capacitive touch HMI panel demonstrating a 8-button keypad, 4-element slider, 3-element wheel and 1-proximity sensor.

Hi Dennis,

thank you for your detailed reply! Now a further question regarding the MSP430FR2632/3 popped up:
For the proximity sensor (and possibly also for the slider) it would be beneficial to use a driven shield electrode. Is it possible to use an unused captivate measurement channel to drive the shield electrode?

If so, I would assume that for the slider this could be done by placing a 4 element slider in the CapTIvate Design Center and using the fourth electrode as the shield electrode. Is this correct?

If possible, how would this work for the proximity sensor?

Thanks!

Hi Stephan,

Yes, you will need a shield to prevent the unwanted affects from a nearby hand or if placing the headset on a table, etc.  You want to keep the on-head sensor focused in only the direction where it can 'see' the head, and not be influenced by things around the sensor.

Here is a document from our FDC capacitive sensing group that helps explain the use of shielding for interference and parasitics.

Technically you can, but the best shield is to use a hatched ground plane as the shield on the side of the sensor you don't want interference.  The problem with this is it dramatically increases the parasitic capacitance of the sensors (slider elements), but if you have the shield in between the sensors and the ground plane, you can recover most of the sensitivity while the ground plane provides excellent shielding.

Here is diagram from the above document showing how the shield works.

And here is how the shield is used to mitigate the parasitics caused by the ground plane.

Now, implementing the shield drive signal must occur at the same time when the slider elements are active.  Unfortunately, the GUI doesn't have the 'smarts' to implement this, so you will need a few of the HAL level functions to enable/disable a specific pin you wish to use as the drive channel.  Let me find some example code and I will share with you to give you an idea how this works.

Hi Stephan,

Here is my recommendation for a 3-element slider configuration using a driven shield.

Select one pin (any pin) from each of the four measurement blocks for the slider elements.  Note, RX0 is split and is on both left and ride sides.  This is the default slider implementation and what is supported by default in the Captivate library.  For information on using a alternative slider implementation see the Captivate tech guide.

Now for the shield you want to connect it as shown.  It must be connected to an unused block, choose any pin.  Somewhere early in code, say after the call to CAPT_appStart(), you want to enable the shield as shown below.  This doesn't activate the pin at this point, but allows this pin to participate when the other blocks are activated during the slider measurement scan.