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MSP430FR4133: Need sample code of capacitive touch for MSP430FR4133

Vipul Garg
Prodigy 20 points
Part Number: MSP430FR4133


Tool/software:

Hi Everyone

i have seen this MSP430FR4133 can drive Capacitive Touch Also, as written in the documents but i don't find and sample code and schematic to go ahead with. If any one can help me out with this I will be very greatfull.

I am struggling with capacitive touch in MSP430FR4133.

Thanks In advance.

  • 0
    TI__Guru 71216 points

    Hi Vipul,

    There is a section in the MSP430FR4xx_2xx user guide, section 9 - Capacitive Touch I/O, that describes how it works and the registers/bits you need to enable it.

    There isn't any SW written for this, so you will have to develop your own.  Reason is we only have SW support for another MSP430 family of capacitive touch MCUs, MSP430FR2676, MSP430FR2633.

  • 0 in reply to Dennis Lehman
    Prodigy 20 points

    Thanks Dennis for the prompt reply.

    there is one more thing i would like to ask, if there is any best practice to connect my touch pad with microcontroller. please help me out with this. like any circuit etc.

    Thanks  

  • 0 in reply to Vipul Garg
    TI__Guru 71216 points

    Hi Vipul,

    When you say "touchpad", do you mean a single "button" or electrode, or do you mean touchpad like you see on a laptop?  Reason is touchpad (aka trackpad) requires a different method of driving the electrodes (mutual capacitance) and the FR4133 does not do this.

    I suspect you mean a single button or touch point, I'll refer to it as the sensor.  In which case all you need to do is connect the sensor to one of the I/O pins that support capacitive touch.  You can see a diagram in the user's guide, pg339.  The cap in the diagram is the sensor.

    I'll copy here for convenience.

    Keep in mind that in addition to the sensor, any wire or PCB trace between the sensor and the MCU is also sensitive to changes in capacitance, so depending on the application and where the sensor is located relative to the MCU, you should consider shielding the trace with a ground.

    There is a lot of information related to this topic in the CapTIvate Technology Guide, Best practices section.

    Now if this only for prototyping and learning how to use capacitive touch, I wouldn't worry about it.  Just know that touching the wire is same as touching the sensor.  NOW, If this is for a product or something produced on a PCB, you want to be more careful and position the sensor where a finger/hand can touch, but the trace should be routed on the PCB that is not accessible to the touch.  Here is an example.  The RED the top side of the PCB (the side a user touches).  You can see the round buttons.  The BLUE is the backside or bottom side of the PCB.  Note that each button has a via between the top and bottom sides that the trace is connected to.  The trace is routed on the backside because it is further away from a potential finger touch.

    The BLUE hatch on the backside is a "ground" hatch, which is connected to ground for shielding from the backside.

    To provide better shielding for the traces, having a "ground" hatch on the top side shields the traces from any touch. See illustration below. However, IMPORTANT, the more ground you have around or under or near the sensor, the less sensitive the sensor will be.  So you may have to experiment a little.

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