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CS1500558: PGA SD ADC and FFT resonant frequency of the measured signal by piezo sensor

Dan Richter
Prodigy 40 points

I was inspired by the Non-Intrusive Tank-Filling Sensor Based on Sound Resonance article.

In my case, I would like to measure whether I will have to empty a full plastic septic tank of about 5 m3 volume by tapping a solenoid on the outside of the septic tank placed in the ground, measuring the response using a piezoelectric sensor and calculating the resonance frequency of the septic tank filling volume using an FFT.

I will then send the measured value using the ATSAMR34 I have to the LoRaWAN network.

I have already ordered the solenoid and the piezo sensor (I can use just the piezo element if necessary).

What chip would you recommend for PGA and Sigma Delta ADC? Is there any chip on the market that would directly process the captured data using FFT and the output would be the frequency of the given volume of the tank that I would just pass to ATSAMR34? I don't need to continuously measure the actual filling volume of the tank, I only want to reliably identify its maximum filling once a day.

Mayabe you can advice me too on simmilar product as the SAMR34 XPLAINED PRO EVALUATION KIT (Microchip) made by Texas Instruments (e.g with DMA for data transfer from PGA SD ADC) which can possible make all required mesurement and LoRaWAN transmission with a few separate chips only.

Your kind advice in this matter would be highly appreciated.

  • 0
    TI__Mastermind 23045 points

    Hello Dan,

    Thanks for posting to the sensing forum! Interesting article thanks for sharing, in your case since you are only interested in identifying if it has reached its maximum fill I believe a more simple solution would be to use ultrasonic technology to identify the level of the tank.

    This is also a non-intrusive way of measuring your tank by using the principle of ToF and should be easier to implement in comparison to the method described in the article. I have attached an image below of how ToF works. Using this method avoids using FFTs and simply uses the time it takes from the signal to be generated and to echo back from the top of the water to determine the level. 

    Here is a document with some more information on how to achieve liquid level sensing using ultrasound: https://www.ti.com/lit/an/snaa220a/snaa220a.pdf

    Unfortunately I am not able to help you with all your questions since I am more familiar with our sensor portfolio and not the other devices mentioned. As far as analog front ends for the knock system and ADC recommendations it might be beneficial to start a new thread regarding an ADC specifically so that your question is reviewed by an engineer from the ADC team that is far more familiar with the portfolio and recommendations based on your application. I know they offer some ADC's with integrated PGA's and some other functionality (possibly FFT?). 

    Same thing would go for the SAMR34 replacement, I believe our microprocessors team would be able to provide a more clear answer on these.

    I hope this helps, let me know if you have any questions!

    Best,

    Isaac

  • +1 in reply to Isaac Lara
    Prodigy 40 points

    Hi Isaac,

    Many thanks for your nice idea. I will think about it.

    Have a nice day,

    Dan