FDC2214: Why does capacitance decreases when the human hand approaches?

Jiho Noh

Part Number: FDC2214

I made a custom board with FDC2214 implemented to detect proximity distance between my sensor and the human hand.

One flat plate is connected to Ch2 INA and another plate is connected to Ch2 INB, which means I am using two plates to detect mutual capacitance.

When I used an LCR meter(a bulky device that can measure capacitance), the capacitance decreases when the human hand approaches the sensor.

However, when I use FDC2214, the capacitance increases when the human hand approaches.

Why does capacitance decreases when I use FDC2214?

Is it something to do with me using a single-ended measuring method?

If I set the firmware inside the board to use the differential measuring method, would the capacitance decrease when the human hand approaches?

over 5 years ago

0 Kristin Jones93 over 5 years ago

TI__Genius 17440 points

Hello Jiho,

The sensor capacitance will always increase when a hand approaches. For capacitive sensing, human targets are comparable to grounded bags of water. When any grounded object approaches the sensor, the capacitance will increase because the voltage stays constant and the target distance decreases.

I do not recommend using an LCR meter for this measurement. You have to specify a specific frequency, but both the capacitance and the inductance of the LC tank sensor change across frequency. The capacitance should be measured at the resonant frequency of the LC tank, which will change as the hand approaches the sensor. If you have access to an impedance analyzer or a network analyzer, these would be better options.

Best Regards,

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FDC2214: Why does capacitance decreases when the human hand approaches?