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LDC0851EVM: Evaluation board does not seem to work.

Lars Wallden1
Prodigy 20 points
Part Number: LDC0851EVM

Hi, I received an LDC0851EVM board and when starting testing I could not get any indication for the presence of metal objects.

The board is just unpacked, powers through USB with the enclosed cable from TI.

I can measure 3V at the VDD test point as well as on the EN and OUT test points. There is no change to the out signal when a metal object is in the presence of the sensor part. The LED does not light up.

Speaking with chat support they advised me to open a case in the forum to establish if the device is faulty.

The product was bought through Mouser UK.

Regards,

Lars Wallden

  • 0
    TI__Expert 7589 points

    Hi Lars,

    Sorry to hear that you are unable to use the EVM. There can be a few points to look at. If you are able to measure the Out pin to be high that indicates that the Inductance of Ls is higher than the Lr. We do recommend that you do follow proper guidelines in handling EVMs with a standard ESD guidelines.

    What is the setting of the switch S2 ? Have you tried the USB and the Coin cell option ? 

    Can you please help us what kind of target is being used ? is it a conductor like copper ? How close was the target to the EVM ?

    There is a trim pot R5 that is adjustable that can be tweaked based on the distance. Have you looked at tweaking the pot to get the response you get ? 

  • 0 in reply to Arjun_Prakash
    Prodigy 20 points

    Hi Arjun,

    I connect the board USB to my PC. The S2 switch is in the position "USB".

    I can measure 3V between the GND and VDD test points.

    With no metal objects close, the board is on a glass table, 

    OUT test point is 3V.

    EN test point is 3V.

    The LED is OFF.

    The trim pot R5 is in the middle position.  Reset is done.

    If I move a metal object close there is no change. I try with coin, large pair of scissors, screwdriver and other tools very close, 1mm from the board sensor.

    If I drop the coin on the board so that it covers the whole sensor laying on the board the LED turns on and the OUT test point is o.3V.

    Lifting the coin 1 mm above the board and it turns off the LED.

    If I turn the R5 put to max sensitivity and use the reset button:

    The same functionality as above, only placing the large coin on the board so the sensor is fully covered gives a signal/turns on the LED.

    If I turn the R5 to min and use the reset button:

    The large coin triggers the sensor when it is half covering the sensor coil and 1 mm above, or fully covering the coil 2-3 mm above the coil.

    The large scissor triggers the sensor if it is 1 mm above the coil.

    The small screwdriver does not trigger the sensor in any way. A larger screwdriver did if it was within 1 mm of the sensor coil.

    My conclusion is that the sensor board works but is only triggered by a large metal object very close to the coil (1-2mm) that covers 50% or more of the coil. Looking more closely on the Youtube videos it seems as if this is the case. The metal object must be very close to the sense coil?

    Is there some way to improve the sensitivity of the sensor?

    Regards,

    Lars Wallden

  • 0 in reply to Lars Wallden1
    TI__Expert 7589 points

    Hi Lars,

    I am glad that you have the board working. Based on your experiments and use cases it does indicate you have a working EVM. 

    I high recommend reading through the FAQ Inductive sensing. Our Inductive sensing devices works on the principle of a highly conductive target when placed above the coil the eddy current generated on the conductor creates an opposing magnetic field when reduces the effective inductance on the coil and our LDC device is able to sense the change in inductance and provide a switched output. 

    The effect of inductance measurement changes with different metal objects, we highly recommend to use a highly conductive target such as copper. The change in inductance is very effective at the outer diameter of the coil not as much as the inner turn. Due to this reason we also recommend that the size of the target be comparable to the size of the coil and perhaps match the coil size. Section 2 of the users guides does explain this as well. 

    In regards to improving the sensitivity of the sensor the variables to change would be the coil design or the target shape. Here is an app note on LDC Coil design that explain the principles of coil design and also provides guidance on designing coil per application needs. 

    Let us know if this help.