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DRV2605EVM-CT: Clicky Mechanical Tactile Feel Using LRA

Myron Richard Dennison
Prodigy 50 points
Part Number: DRV2605EVM-CT
Other Parts Discussed in Thread: DRV2605, USB2ANY, DRV2625EVM-CT, DRV2625

Hi, 

I am very new to haptic and I am currently working on a project where the tactile feel when you press a virtual button, needs to be like that of a clicky mechanical switch. 

I am playing around with the default modes of DRV2605 Haptics EVM, while waiting for the USB2ANY, but there's nothing there that is comparable with mechanical click.

So, I am wondering if that can be achieved using an LRA. 

Appreciate any inputs.

  • 0
    TI__Expert 8711 points
    Myron,

    The best waveforms to achieve this will be waveform 1 or 4. The quality of the click is more dependent on the LRA than the driver. The LRAs on the EVM are not the best, so I recommend finding a higher quality LRA. Also, I would suggest trying the DRV2625EVM-CT (doesn't need USB2ANY). This IC is newer and has better features to support very short clicks.
    You will not get fast enough rise/fall time with an ERM.
  • 0 in reply to Kelly Griffin
    Prodigy 50 points

    Hi Kelly,

    Can you recommend a specific LRA that I can purchase to achieve this?

  • 0 in reply to Myron Richard Dennison
    TI__Expert 8711 points

    There are a few vendors that can provide high quality LRAs to achieve this effect. We have vendors listed here.

  • 0 in reply to Kelly Griffin
    Prodigy 50 points
    Is there a particular spec (frequency, amplitude, etc) that I need to be looking at? I have tried 10 different LRAs using the HCC and I can't find any combinations close to a mechanical click so far.
  • 0 in reply to Myron Richard Dennison
    TI__Expert 8711 points
    Hi Mryon,

    Due to the rise and fall time of the LRA, you will not achieve exact mechanical clicks. The mechanical clicks we have measured in the past are ~5ms long. The quickest LRAs I have tested have a rise time of ~8ms; that is just the rise time. If you can get the entire click to happen under 20ms, it should feel very crisp to the user, similar to a mechanical click.
    Using the DRV2625, I suggest using max VDD voltage of 5.5V, setting the OD_Clamp to 0xFF, drive the actuator in open-loop mode, and enable AUTO_BRK_OL. This will drive the actuator with more energy at the beginning of the waveform because it is in open-loop (make sure you set the frequency). The closed-loop braking will insure a quick fall time. You cannot do this with the DRV2605, because it does not have the auto-brake feature out of open-loop. You can try just using the open-loop feature of the DRV2605 though..

    If you want to truly achieve this effect, you will have to use piezo haptics.
  • 0 in reply to Kelly Griffin
    TI__Expert 8711 points
    Hi Myron,

    Let us know if you have additional questions.