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Questions about FDC2214PROXSEX-EVM

hideyuki sakai
Mastermind 6250 points
Other Parts Discussed in Thread: FDC2214PROXSEN-EVM, FDC2214

Dear, Sir.

My customer would like to detect around several cm to 50cm distance, so we

introduced FDC2214 & FDC2214PROXSEN-EVM for him.

Now, he is considering to purchase the EVM. Proximity Sesor will be utilize

the such range(distance) deteaction.

In advance, he is asking sevral questions about it. Please give your advice.

1. Range(distance) Detection around several cm.

a) Figure 5 on the user's guide show the distance vs. Cap change from baseline.

But it is Capacitive Touch Buttons. LC tank values is same as both Buttons &

Proximily.

Is it possible to detect around several cm range utilizing Proximity Sensor?

b) Looks like 1cm would be the limit of range detection utilizing Buttons.

I wonder the range limit could be expected same as Buttons when

utilizing Proximity Sensor?

Best Regards,

H. Sakai

  • 0
    TI__Expert 6480 points
    Hi H. Sakai,

    The sensing range will be based largely on your sensor size. Since the proximity sensor is larger, it will be able to detect a target within the tens of cm range. The button sensors are slightly smaller and so its sensing range will be smaller, maybe around 5cm - 10cm.

    We also have an app note online which further details how sensing range is related to the size of the sensor: www.ti.com/.../snoa940.pdf.

    Thanks,
    Rachel
  • 0 in reply to Rachel Liao
    Mastermind 6250 points

    Dear, Rachel-san. 

    Thank you so much for your valuable advice. 

    Sorry again, but I would like to double-confirm as followings. 

    I guess sensor size & minimum sensing range(distance) would be

    determined by the theory of capacitor(C = Dielectric constant of Air * 

    Sensor size / Distance) and Lowest resonant frequency on FDC. 

    So, the size become larger, Resonant frequency would be out of 

    control too lower due to larger C. 

    1. I wonder above my guess is correct? 

    2. Using FDC2214PROXSEN-EVM and utilizing the combination of

       Proximity & Touch Button, Does it mean that From 5cm - 10cm TO tens

       of cm will be undetectable range without any sensor size adjustment?

    Best Regards, 

    H. Sakai

  • 0 in reply to hideyuki sakai
    TI__Expert 6480 points

    Hi Sakai-san,

    1. The resonant frequency is mainly determined by the capacitance of the tank and any parasitic capacitance on the board. When combined, the total capacitance may be around the order of tens of pF. The capacitance coupling between the hand (at the threshold of detection) and the sensor will only be on the order of fF so the sensor size will not significantly affect the resonant frequency. 

    2. I'm not entirely sure what you mean by utilizing the combination of the proximity and touch button sensors? When only using the button sensor, the detection range may be around 5-10cm. When only using the proximity (bezel) sensor, the detection range may be around 15-20cm.

    Thanks,

    Rachel

  • 0 in reply to Rachel Liao
    Mastermind 6250 points

    Dear, Rachel-san. 

    Thank you for your correction for my miss-understanding and sorry again. 

    The Proximity(bezel)'s large size is to detect the small fF order capacitance

    over long range. 

    1. Does it mean the Proximity(bezel) could detect the closer range

        as 1cm? 

    2. I mentioned about "multiplexing operation". 

        Considering the trade-off between sampling rate & resolution, 

        Will multiplexing operation be more suitable to detect from long range to closer

        range as 1cm. 

    Best Regards, 

    H. Sakai

  • 0 in reply to hideyuki sakai
    TI__Expert 6480 points

    Hi Sakai-san,

    1. The proximity (bezel) sensor can definitely detect at a closer range such as 1cm. When I said the sensing range could go up to 15-20cm, I meant the maximum sensing range. All distances in between will also be detected.

    2. There is no need to multiplex the operation. You will only need to change the threshold so that the system will not detect proximity until the target is within the 1cm range you want.

    Thanks,

    Rachel

  • 0 in reply to Rachel Liao
    Mastermind 6250 points

    Dear, Rachel-san. 

    Thank you so much for all of your teachings & advice. 

    My questions have been cleared. Thanks a lot. 

    Best Regards, 

    H. Sakai

  • 0 in reply to hideyuki sakai
    TI__Expert 6480 points
    Hi Sakai-san,

    Not a problem!

    Thanks,
    Rachel