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FDC2214: FDC2214 for a connected sole

Alban Le Piver
Prodigy 10 points
Part Number: FDC2214


Tool/software:

Hello, 

I'm actually working on a design with the FDC2214. 
The project is a connected sole with capacitive sensors on it. The goal is to have a representation of the distribution of the weight of a foot on a sole. All the sensors are represented by a matrix of 11 lines and 8 columns. The same way as a keyboard for example. 

The sole includes  around 80 sensors. For each sensor 1 plate is connected to the FDC2214 using 1 of the 11 lines and the other plate is connected to ground using 1 one the 8 columns. 
To control the differents lines we are using 3 FDC2214 so we can control up to 12 channels (lines). And to control the columns we are using a multiplexer to connect the selected columns to ground. 

For example, selecting sensor n°32 is selecting the line 3 and columns 2. To do this we will activate the channel 3 of the FDC2214 n°1 and connect the columns 2 to ground. We will do this for each sensor to have a representation of a foot on the sole by comparing all the value measured. 

We choosed to used the FDC2214 in single ended with one plate to ground to minimize the number of cables and the complexity.

I wanted to have your feedback about this project on how we can use the FDC2214. Maybe there is a better way to do this ? Or maybe you had already a similar project ? 

Thanks in advance,

Alban Le Piver

  • 0
    TI__Mastermind 40295 points

    Alban,

    Thank you for considering our devices.

    This is the first time I have heard of this approach. It sounds like it has a lot of promise.

    Our inductive and Hall sensors might be made to work as well, but each would have some disadvantages compared to the capacitive sensor.
    An inductive sensor would need to have coils embedded in the sole, which may have some disadvantages compared to the simpler square sensors.
    It would also require require two conductors per sensor.
    Hall sensors would require the actual devices to be embedded in the sole, and magnets to be embedded in the insole, which would be tricky to say the least.

    Some factors to consider with capacitive sensing:

    1. The permittivity and conductivity of any layer between the sensors and the foot will need to be low so the layer does not act as a shield between the sensors and the foot.
    2. Consider the effects of moisture (sweat) build-up in the system. That could impact your capacitance/pressure estimates, especially over time.
    3. EMI can be a consideration in some capacitive sensing systems because of the antenna-like nature of the sensors.
      Since the system is footwear-based, the sensors will be between the ground and a human foot, and these would probably serve to attenuate EMI. 
      Please be sure to consider EMI in your design as you move forward because some of our customers have struggled to get to production with the FDC2x1y family of parts because of EMI.

    Regards,
    John