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LDC1000 newbie

LPs
Prodigy 40 points

Hi all,

  I'm trying to make a LDC1000 working to do a rotation sensor.

The communication is wworking well, but data is strange.

I set up as follow:

- TBCLK = 7,1 MHz connected to a PWM output of my uP

- This is the init of registers

LCD1000_writeSingleReg(LDC1000_CMD_RPMAX, 0x14);
LCD1000_writeSingleReg(LDC1000_CMD_RPMIN, 0x3B);
LCD1000_writeSingleReg(LDC1000_CMD_SENSORFREQ, 0x53);
LCD1000_writeSingleReg(LDC1000_CMD_LDCCONFIG, 0x12);
LCD1000_writeSingleReg(LDC1000_CMD_CLKCONFIG, 0x00);
LCD1000_writeSingleReg(LDC1000_CMD_INTCONFIG, 0x04);

LCD1000_writeSingleReg(LDC1000_CMD_THRESHILSB, 0xFF);
LCD1000_writeSingleReg(LDC1000_CMD_THRESHIMSB, 0xFF);
LCD1000_writeSingleReg(LDC1000_CMD_THRESLOLSB, 0x00);
LCD1000_writeSingleReg(LDC1000_CMD_THRESLOMSB, 0x00);

LCD1000_writeSingleReg(LDC1000_CMD_PWRCONFIG, 0x01);

What I saw is that proximity data is not so stable: Rp value vary at the second decimal digit, amd sometimes more.

The ODR is always the near the same values: it vay from 119 to 124 digital value read from registers.

Is it a usual behaviour or is there something I'm doing wrong?

Regards

  • 0
    TI__Expert 4890 points

    Hi,

    Just like ADC, there is some noise in LDC1000 output, and the noise change with system condition,  such as coils, approach. You can use a inductor to check if it is work well, Or give more description and data to help us check the problem.

    Thank you!

    Sunny.

  • 0 in reply to Sunny Qin
    Prodigy 40 points

    Thank you for your fast reply.

    I'm thinking that is not the application I need, because of is not accurate enough to do absolute encoder with a precision of 0,1°.

    Otherwise is it correct that ODR register moves around the same values? 119-124?

  • 0 in reply to LPs
    Prodigy 40 points

    Ok,  I changed parameters, using:

    fsensor = 6.250.000 Hz

    Amplitude 4V

    Response time 6144

    I can see ODR values vary from 3340 to 4000, with a 180° rotation.

    The goal is very far: 0,1° means to have a variation pf 1800 instead of 500 that I can see now.

    Is my conclusion correct? Is this device not applicable for an absolute encoeder or are there some technics to improve tghe resolution of ODR?

  • 0 in reply to LPs
    TI__Expert 4890 points

    Hi,

    You can use Inductance to measure rather than Rp, then use 100 piont or more moving average filter to get down the noise,  I think you can achieve your goal.

    Thank you!

    Sunny.

  • 0 in reply to Sunny Qin
    Prodigy 40 points

    Hi Sunny,

       I don't understand what you mean with Inductance: is not inductance derivede from ODR register?

    What I trying now is to use raw data of proximity register, that give me a number that vary from 4K to 25K, but seems to be too noisy. I'm trying with different average techics to se if I can reduce the noise....

  • 0 in reply to LPs
    TI__Expert 4890 points

    Hi,

    Yes, ODR register is just the indutance data, you can use large inductance and high Q coil, then we may get more counts. Or you can use moving average filter after you get the data.

    Thank you!