Society of Robots - Robot Forum
Electronics => Electronics => Topic started by: voyager2 on August 30, 2010, 07:45:22 AM
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Hi All
First thing, this is for my fish (I bet you guessed that anyway)
I need a for my fish to communicate with my computer 2-4 meters away.
The fish end needs to be as small as possible, 2cm3 is probably max size.
The computer end doesn't really matter, so long as it is either USB or serial, and works with Hyper-Terminal.
And it can't be really expensive either...
Apparently water blocks radio waves, but how does a remote control sub work then ???
Voyager2
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Water slows down the propagation of EM waves. A toy sub at a low enough RF frequency will work for a meter or two before the effect kills the signal. 2.4Ghz will hardly go a few inches. You can try to find very low frequency radios, but it would be 100x easier to just use a tether.
The proper underwater robots i use at work (I work for the Navy) have acoustic modems to communicate underwater.
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Rc subs use the low frequency range which can work in shallow depths, its the high freq stuff that gets blocked very easily.
I would recommend just using a tether system, it is just so much easier to do so. If youve seen some robot fish in research, they start out tethered which makes it easier to focus on more important problems, not annoying things like batteries and recovery
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How about ir leds? It would be limited to line of sight, but its cheap.
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Im going to say tether it with ethernet cable or something similar.
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How about ir leds? It would be limited to line of sight, but its cheap.
Careful with that one, because unless the IR leds are underwater, you will limited to a line of Refracted sight ;)
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How about ir leds? It would be limited to line of sight, but its cheap.
Your not going to get much out of that either. Red light is rather weak, IR even weaker. It will absorbed by the water rather quickly.
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If there's such a thing a Infra Blue, I might try it out, non of you ever read one of these optics books?
Well Blue and Greens travel well through water, that's way the oceans blue-green.
Red and yellow is quickly absorbed due to its short wavelength!
I don't mind tethered, but since part of the fish is likely to be above water it might be possible to have a link...
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I was thinking though, is it possible to use long-wave?
Blue light has long waves...
Or should i make a 555 timer transmitter (I've heard its possible) that transmits at 64 Hz?
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If there's such a thing a Infra Blue, I might try it out, non of you ever read one of these optics books?
Well Blue and Greens travel well through water, that's way the oceans blue-green.
Red and yellow is quickly absorbed due to its short wavelength!
http://en.wikipedia.org/wiki/Visible_spectrum (http://en.wikipedia.org/wiki/Visible_spectrum)
Red has a longer wavelength than say blue or violet.
Infra-blue would be ... cyan I guess ? I think that's not what you meant :)
Higher frequency is ultra-violet. UV LEDs do exist, but I doubt it will solve your problem.
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If there's such a thing a Infra Blue, I might try it out, non of you ever read one of these optics books?
Well Blue and Greens travel well through water, thats way the oceans blue-green.
Red and yellow is quickly absorbed due to its short wavelength!
Infra-blue, interesting. Based on the latin meaning for the term 'infra', which is "below", (because Infrared has a Lower frequency than red) wouldn't "infrablue" then just work out to be a green?
Perhaps some ultraviolet data communication system might work. That way you could wirelessly communicate with your fish, AND possibly disinfect your fishes aquatic environment at the same time!!! ;D :D
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what about something like a 100mw green laser? have one on each end and a system that aligns it and with sensors to receive the data as pulses?
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Since part of the fish is likely to be above water in the early stages of development, IR might do...
I've got some IR leds and a photo resistors, but my guess is that a photo resistor doesn't react fast enough...
I think i have some photo transistors, from a computer mouse, they might be fast enough, i'll have to test them.
Also two way would be nice...
@Chelmi
http://en.wikipedia.org/wiki/Visible_spectrum#Spectral_colors (http://en.wikipedia.org/wiki/Visible_spectrum#Spectral_colors)
Top right, wavelength is measured in nm (nano-meter)
@Blackbeard a system like that could work for 100s of meters, however it would be large and cumbersome, however it would be useful for larger systems.
It would be limited by the horizon and refraction (and line of sight).
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@Chelmi
http://en.wikipedia.org/wiki/Visible_spectrum#Spectral_colors (http://en.wikipedia.org/wiki/Visible_spectrum#Spectral_colors)
Top right, wavelength is measured in nm (nano-meter)
Yes, I know that. Your sentence "Red and yellow is quickly absorbed due to its short wavelength!" did not really make sense since blue has a shorter wavelength and is less absorbed.
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I did a google search on "absorption of light in water" and found these articles that seem to be more on subject.
http://www.d-a-instruments.com/light_absorption.html (http://www.d-a-instruments.com/light_absorption.html)
http://oceanworld.tamu.edu/resources/ocng_textbook/chapter06/chapter06_10.htm (http://oceanworld.tamu.edu/resources/ocng_textbook/chapter06/chapter06_10.htm)
As to a link to the 'fish bot', low frequency radio does work. One can easily receive AM broadcast stations (550-1550kHz) several meters or more under water. Here is a link on this subject:
http://www.qsl.net/vk5br/UwaterComms.htm (http://www.qsl.net/vk5br/UwaterComms.htm)
This would restrict the data rate but for simple commands this should be a problem
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Low frequency radio, seems like a good challenge to make one myself...
All the fish is sending is light levels, and in the future battery level info, it's not like it's sending live feed video.
Could I use a 27MHz toy car transmitter? I've got 2, and there pretty small.
I'll see what else i can do...
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Low frequency radio, seems like a good challenge to make one myself...
All the fish is sending is light levels, and in the future battery level info, it's not like it's sending live feed video.
Could I use a 27MHz toy car transmitter? I've got 2, and there pretty small.
I'll see what else i can do...
you can try but AM is much better since it operates at a much lower frequency. AM is an absolute pain in the ass so expect as much though.
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I think I'll try the IR LED approach, it's not like I'll be using a bootloader to program...
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Sounds good. I would first try using a tether for communications, and then go for IR. You could probably get away with quite small gauge wire for the tether also, as the water would probably dissipate any heat pretty quickly.
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I have some ultra thin wire from a PS2 controller cable, I can tell that IR is not going to be good for bootloading