• State TI Thinks Resolved
  • Locked Locked
  • Replies 1 reply
  • Answers 1 answer
  • Subscribers 79 subscribers
  • Views 348 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

CAPTIVATE-FR2633: Detecting smaller objects (like grapes)

Albert
Prodigy 80 points

Part Number: CAPTIVATE-FR2633

Tool/software:

Hello,

We're using a CAPTIVATE-FR2633 with FR2633_CAPTIVATE_BSWP and other custom projects (like just one proximity sensor connected).

We've been trying to get a different approach at detecting smaller objects such as grapes by using a cylindrical coil with a cylindrical ground plane with unconsistent results.

We're able to detect the grape sometimes (tied to a non-conductive string such as a thread, but within the same day, or even within the same period of 5 minutes of testing, we don't get consistent results and we haven't been able to do so.

The main value we modify is conversion count, as it's the one that increases the sensibility the most.

Is it a reasonable thing to approach for to be able to detect, or is it physically not possible? We are also considering to aim for even smaller objects, hence the grape detection is the first approach that we would need to pass.

Thanks in advance

Greetings,

Albert

  • 0
    TI__Guru 71216 points

    Hi Albert,

    Keep in mind that the grape, or any object as a matter of fact, must have a strong capacitive coupling to ground in order to cause a change in the sensor's capacitance.  This is true for both self and mutual capacitive sensors.  So in your setup, the grape does contain lots of water and if placed properly such that a portion of the grape is on the coil and a portion is on the ground plane, that should work.  I don't know the relative size of the grape to the size of your sensor, or your layout.  Is this something you could share?  If you don't want to expose this information you can send me a friendship request and share this information confidentially.

    Now, as it turns out, if you use a mutual capacitive sensor and set it up such that when the grape passes between the RX and TX electrode, the grape will change the dielectric constant, causing a change in counts, but in the opposite direction (lower counts instead of higher counts).

    I have attached a pdf showing some experiments I did with a self and mutual capacitive sensor to see if it was possible to detect the presence of a pill (like an aspirin).  You will see from the data the mutual is very sensitive to the pill due to it's effects on the dielectric between the TX and RX electrodes, as compared to self cap mode.

    pill detection with captivate.pdf

**Attention** This is a public forum