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Topic starter
2021-12-20 1:46 pm
Hey everyone, new guy here and to Arduino. Super excited to jump in and learn electronics.
For my fist real project I wanted to make "simple" depth recorder and water temperature monitor for my kayak. For those not familiar with fishing, these units are generally large with transducers that mount under the water line on a boat or kayak and provide sonar readings of depth and most now provide some visual indication of the underwater structure and possible fish presence. Oh and water temperature...
I fish out of a kayak in fairly shallow water (8-10 max, most times under 3 feet) and I wanted to build a super basic version that displays water depth and temp in numerical format only on a small lcd display.
I ended up here after watching Bill's video on the A02YYUW, which I ordered before watching his video. He noted that while waterproof the readings are not accurate for determining distance in water. So now I am wondering:
1. Is there a calculation I can perform on the results returned from the sensor to get the correct(ish) (+- 2 inches) distance in water? Bill mentioned it was due to the speed of sound being different through water vs through air.
2. Is there another transducer I should be using?
3. Would a LiDar module be a better way to go?
I should note that I could also attempt to use a transducer from a fishfinder manufacturer, but I am unclear if it would work on an Arduino or it is encapsulated in some proprietary encoding/encryption, plus they are fairly expensive, $60+.
Thanks everyone excited to be here!
Mark Bolton reacted
2021-12-20 6:41 pm
@gulfstreamoutdoors
Just some random thinking about your project ...
There seems to be a lot of variations in the estimates of the velocity of sound in air, fresh water and salt water. However, using the figures from Wikipedia at
https://en.wikipedia.org/wiki/Speed_of_sound
V(air) = 343 m/s
V(fresh) = 1481 m/s
V(salt) = 1500 m/s
If the sensor read distance is called D, then you would need to rescale the (air based) distances as follows
D(water) = D(measured)*1481/343 = 4.318 * D(measured) for fresh water
D(salt) = D(measured)*1500/343 = 4.373 * D(measured) for salt water
But remember that the sensor’s minimum distance also needs to be scaled up (in order to allow the sound time the “ping” is issued until the receiver is prepared to receive the return signal).
Also, the error must be scaled up, so if the sensor error in air was 1 cm (less than half an inch) the error in water will be 4.317 cm (almost 2 inches which is already your “worst case” desired range).
Also, this analysis doesn’t account for temperature differences (which will be significant) nor thermoclines (although they’re somewhat unlikely in only 3 metres of water).
Hope this helps you get started.
Anything seems possible when you don't know what you're talking about.
Topic starter
2021-12-21 2:49 am
@will Thanks for the reply, super helpful! Glad to hear I was at least thinking along the right path. Really appreciate the formulas. I can live with +-6 inches even so I am going to give this a go and see where it leads. I wonder how the "pros" handle all those variables 🤔
2021-12-21 2:56 am
As a follow-up, since you're planning on including a temp sensor as well, here's an URL where you can find a table of velocity corrections for sound in water at various temperatures.
https://www.engineeringtoolbox.com/sound-speed-water-d_598.html
Anything seems possible when you don't know what you're talking about.
GulfstreamOutdoors reacted
2021-12-21 3:11 pm
Hi @gulfstreamoutdoors, As @Will has described, the accuracy of your calculations will depend on several variables.. the density of the medium (water in this case) whether it is fresh or salty, and temperature.
As density increases, the speed of sound will decrease, but as temperature increases, the density will decrease, thus this needs to be considered to get any true correlation of density and temperature to the speed of sound. Looking forward to seeing how your project progresses..
regards,
LouisR
GulfstreamOutdoors reacted