underwater fish detector

[fedi_makni]

I would like to create an underwater fish detector - completely operating underwater (personal project)
The enclosure will be a waterproof hollow cylinder (possible material to use are: acrylic, Polycarbonate or PVC), a PCB will be sealed inside that enclosure containing the sensor (the sensor of choice should not be waterproof because it will be inside a waterproof enclosure).
The fish can pass through that hollow and will be detected while passing. the inner diameter of the enclosure will be in the centimeter range to allow one fish to pass at a time.
Note:
I am not dealing with precise measurements or long range (no need for those expensive high precision sensor)
I cannot use big or expensive sensors due to budget related reasons and size constrain
max operating voltage of the PCB is 12V (preferably 5V or 3.3V)
Here's a link to picture that illustrate the idea for better understanding
http s://drive.google.com/file/d/13LIXOK5Zvt1R61uHieQIGLCPWyVfH69t/view?usp=drive_link (removespace)
I am using 2 sensors so i can make sure i detect that it passes through
optional receivers can be implemented if the sensor i use is just a transmitter and not transducer

Here comes the challenging part, the sensor choice, i will list some i thought about and i hope i can get some ideas from you that can help me.
- Ultrasonic sensor (i saw some people successfully did it but nothing is documented with low cost sensors):
Challenges:
Blind distance of ultrasonic sensor for small measurements.
I don't know if the acoustic wave can pass through acrylic hit the fish and be detected
- Optical sensor (such as VL53L1 or any other choice)
Challenges:
Require clear water
water can scatter the light but i am using it for short distance so i don't know if it will work or not
require transparent enclosure
- ESP32 camera (image recognition algorithm)
Challenges:
Require complex algorithm
Require clear water

I would like to hear if you have any other idea or if i can improve one of the suggested ideas to successfully achieve the project.
Thank you very much.

 

[barry]

without a dimension, that drawing is meaningless. what’s the diameter 10cm? 2 km??

 

[fedi_makni]

without a dimension, that drawing is meaningless. what’s the diameter 10cm? 2 km??

If you actually read the question, you will see that i mentioned:
the inner diameter of the enclosure will be in the centimeter range to allow one fish to pass at a time.
but i think you didn't focus about the post itself. thank you anyway.

 

[KlausST]

With this response ... I´m frigthened to post anything "wrong" that does not suit your mood.
Sadly I´m a human that makes mistakes. Be glad that you are perfect.

Klaus

 

[fedi_makni]

@KlausST
I didn't say that, but if someone is just saying "that drawing is meaningless" without actually reading the post and he just respond like that, do you think that's a good practice? And in reality i didn't say anything, i just said i mentioned the information you asked about in the post, that just means he didn't read it and directly prejudge the entire post and write a comment without checking. I don't think my response was offensive compared to his response.

 

[danadakk]

There is always the possibility of using a capacitive approach,
fish becomes dielectric change. Google this.

But because of various possible water changes, PH, contaminants, I would
start with adaptive optical post using three light sensitive elements, one
for reference out side tube, two inside for direction. Use reference to
adjust decision from two interior ones.


Regards, Dana.

 

[fedi_makni]

There is always the possibility of using a capacitive approach,
fish becomes dielectric change. Google this.

But because of various possible water changes, PH, contaminants, I would
start with adaptive optical post using three light sensitive elements, one
for reference out side tube, two inside for direction. Use reference to
adjust decision from two interior ones.


Regards, Dana.

Thanks for the response.
I was thinking about the capacitance approach but i couldn't figure out how to do it, should two plates be exposed to the sea water and then measure the capacitance between them?
Could the salt affect that overtime?
If the fish pass too fast, will the capacitance change be noticeable?
What do you think?

 

[danadakk]

Fish velocity is so low relative to computing detection methods I think would not be
of concern.

Fish would change the dielectric, so yes two plates they swim between. Or two split
cylinders. I still think you need a reference capacitor where no fish involved, just
a detection of the water chemistry, pollution.

Electrical properties salt water, take a look at this :

Understanding and optimizing fish counting techniques based on electrical impedance measurements - PMC

Sustainable aquatic resources management requires reliable methods for fish detection in various environmental conditions. Herein, we study fundamental mechanisms underlying the application of electrical impedance measurements in this regard. We ...

www.ncbi.nlm.nih.gov

Regards, Dana.

 

[D.A.(Tony)Stewart]

Thanks for the response.
I was thinking about the capacitance approach but i couldn't figure out how to do it, should two plates be exposed to the sea water and then measure the capacitance between them?
Could the salt affect that overtime?
If the fish pass too fast, will the capacitance change be noticeable?
What do you think?

Capacitance detection will not be detectable for fish in a tube of water. The capacitance would be very low with only water and the same with fish in the water. This is because fish also have high dielectric constant and extremely low sensitivity well below noise and tolerance levels.

An array of optical interruption emitter/detectors is the lowest cost method to consider for reliable detection somewhat like golf ball detectors in simulators.


Here is an example of Dk directly on fish. (b) is much the same as water (80). Here they used various UHF frequencies with expensive methods of dielectric constant measurement.

But before you consider any method, you must make a list of many questions and answers to define what you expect and can tolerate.

e.g.

1. What size? in maximum diameter or weight, determines the maximum spacing of an array emitter/detectors in the radial direction (R)
2. How fast? This determines the maximum spacing of detectors in the Longitudinal direction (L) to avoid multiple counts and validate potential false triggers.
3. How reliable? Error rate for False positives? and True Negatives?
4. How is much data to collect? how often, how to collect? User Interface?
5. What budget for prototypes? materials? tools? R&D time? or shopping time?
6. Describe the purpose and consequences you expect?
7. How convenient is your intended location?
8. What assistance is available to you?
9. What is your DIY skill level?
10. How do you force a tiny and big fish to go thru the same detectors one at a time without going back over and over? (V-trough ? )
11. How often do you intend to clean it from getting clogged by sludge, twigs, organic material
12. Is this an existing pipe?