Larry,
My comments below...
> -----Original Message-----
> From: Larry Sanders [mailto:rhatman@earthlink.net]
> Sent: Friday, December 20, 2002 08:34 AM
> To: slug@nks.net
> Subject: Re: [SLUG] A Challenge....
>
>
> Chuck
> Remember the magic words: "all you gotta do" !
Yes like the "oh yea that is easy"
> Here are a few engineering questions.
> What are the dimensions (HxLxW) of the pinfish and pigfish?
These guys can range from 1X2.5X.5 to 3X7X1.5 inches
though we delivered one last night that was really big enough
to feed a person and leave them full.
> This is the area that will interrupt the IR beam.
> Does the IR detector signal on/off or an analog signal?
I can go either way with this one, I figure a ON/OFF is
probably the best way as it will not require a A/D conversion.
I have also thought about using bluegreen to blue LED's with
sensors optimized for that part of the spectrum because it
is water frendly.
> If it is an analog signal then how will you do a D/A converter?
> This is a key question if the spacing between the detectors is
> significantly less than the size of the fish.
Yes, from what I have seen of the Icelandic product as the fish
moves through the sensor it "images" the fish and then looks at
the "image" to figure out if it is a fish. Also it checks to see
if there is another fish "tailing" the first one just in case
the second one has pushed up beyond the tail of the first one.
> Is the sluice also pouring water or just allowing the fish to swim?
yes, the sluice is a "V" shape, it is inclined downward at a angle
such that the fish follow the flow of water into the sluice which
narrows down to the exit point which is where the sensor is located
This address is the web page where this counter is located
http://www.vaki.is/Forsida/Enska/Menu.htm
There are 4 images on the screen, the upper lefthand one of the fish
exiting the sluice is the one to click on, you can see more detail
on that page.
They also have a image system that counts fish in a tank but it is
for even more volume.
> If you are counting from a verticle view, then the sluice should be
> shallow and the detectors close togeather. Or if the detectors are
> horizontal then the sluice can be narrow and possibly deeper.
> It will be less complicated if the water flow is zero and the fish are
> swimming between the two tanks. Then you can get them to
> line up like a cattle gate.
The detectors would be vertical or on leg of the 'V' at the mouth
of the sluice.
> In one post you mentioned that you would like to be accurate
> within 5 fish. Five fish out of how many? What percentage?
I should have given percent, %98 would be a good target to shoot
for, I could probably get away with %95. We only get 25 cents/fish
so we can not give away many, and at the same time we do not want
to shore change the shops or they will go elsewhere.
> The problem of counting has been asked before in the field
> of industrial engineering. Significant time invested in a search
> for publishd papers and solutions will definately be worth it.
Most of the solutions are for fresh water fish, and use a
tube with a set of 3 metal rings inside the tube, as the fish
swim past the rings the water conductance changes registering
a count, these devices are not expensive running about $200-400.
The optical counter system which will handle salt water fish
is nother issue, at $5250/unit it is a bit steep for counting
pin fish.
>
> The key to this is the D/A converter and the corresponding
> signal processing. The sample rate should be 100 times the
> rate of the fish in order to recognize a pattern the typical
> pattern of expanding/decreasing shaddow to seperate two
> fish head to tail. If a fish swims by at 1 per second then a
> sample rate of 100/sec or 1 in 0.01 seconds is not to fast
> to process with today's cpu's. The software will ask at each
> sample: is this shadow getting bigger or smaller?
> All you gotta do is count the fish.
That is a very good sum of it, and now all I have to do is come
up with the software part, hardware I do not see trouble with.
I have both PIN diodes and photo transistors, there are also
linear arrays of these things that would do exactly what I
want to do on the hardware side. Now just to figure out how to
to it.
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