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LDC1612EVM: Inductive sensor detecting hand

Kelvin Boateng
Prodigy 10 points
Part Number: LDC1612EVM
Other Parts Discussed in Thread: LDC1612

Hello!

I made a custom sensor for ch0 of the LDC1612EVM using some enameled magnet wire. The inductance of the coil is  67.35 μH with series resistance 1.2 Ω and the parallel capacitor is 22 pF.

Whenever I bring my hand near the sensor, the raw output code value drops comparably to the amount the raw output code value increases when a metal object is brought closer to the sensor. Is the hand capacitively coupling to the circuit and raising the capacitance (since the raw output codes are proportional to frequency, the C or L value is increasing which lowers the frequency I think)? Is this related to the low value of the capacitor used in the sensor LC tank?

When I do the same test with the included sensor, the magnitude of change in the raw output codes from the hand vs the metal object is not comparable in size. Thanks in advance for the help!

  • 0
    TI__Genius 10070 points

    Hello Kelvin,

    I would recommend using the Inductive Sensing Design Calculator Tool to make sure that your coil design is within the parameters of the LDC1612. From a quick look, it shows that your sensor amplitude may be too low (sensor amplitude should be in the range of 1.2 to 1.8 Vp). Additionally, the LDC Sensor Design application note covers what parameters should be considered when designing for a specific application.

    Best regards,

    Nicole

  • 0 in reply to Nicole Khoury
    Prodigy 10 points

    I checked the oscillation amplitude using an oscilloscope, and right now the pk-pk voltage is 3V with the lowest current drive setting. Do I need to use thinner wire to increase the DC resistance of the coil and drop the amplitude? Also this isn't a PCB coil, so I'm unsure if I can use the tool in that spreadsheet.

  • 0 in reply to Kelvin Boateng
    TI__Genius 10070 points

    Hello Kelvin,

    You can set the current drive to ensure the sensor amplitude is within the range of 1.2 to 1.8 Vp. You can individually set the current drive of each channel (between 16μA and 1.6 mA) by using the IDRIVEx register fields. Additionally, section 7.3.5 of the LDC1612 datasheet has further detail on sensor current drive control.

    Best regards,

    Nicole