If i put one SMiRF into a plastic waterproof box, and put it in water, does the other SMiRF (on ground surface) will be able to communicate with the one in the box, under water??? (assume at a depth of 30ft)
OK, short answer: no.
Long answer: most likely no. Water is a great blocker of radio waves. The longer the wavelength, the more likely the radio will penetrate it. There is a chance that the SMiRF will work in water, maybe even to 30 ft, but I can’t say without being an RF engineer. My gut feeling is “only a few feet in clean water”. Distilled water in theory won’t block the radio waves, but no water in practice is or remains that clean.
Now, if this water has any dissolved chemicals or salt in it, forget about it. The higher conductivity of the water makes it an even more effective blocker. Radio above the Kilohertz range will not penetrate at all. And most of the systems that do penetrate are quite powerful because of the loss associated with penetrating water.
… any one can suggest me any wireless control under water?
I have to build a robot to go underwater as a course project…
it will be mounted with a camera, and hopefully a wireless system
I am currently thinking to build a bug (with 6 or 8 feet) that could go both underwater and on ground…
Good question. As mentioned in the other reply, 2.4GHz radio is clearly not in this list. So you need an extra underwater interface, with probably a special protocol since 1Mbps is not attainable.
Options:
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LF radio communications (carrier < 8kHz, only up to 1 kbaud)
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Acoustic waves, read http://www.edn.com/contents/images/60930.pdf
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Visible light communication, read http://www.araa.asn.au/acra/acra2004/papers/schill.pdf
I think the last options takes less time, and the components are cheapest and simplest, and the expected data rate is the highest.
Components for IrDA are commercially available for simple interfacing (free samples via maxim-ic.com): www.maxim-ic.com, look for IrDA (MAX31xx series)
Limitation is that the remote control must be within a certain angle above your ‘bug’, because for large incident angles the air/water surface is reflective. To avoid that, you might want to immerse the rc.
If you are good at preamplifier electronics, I think you can improve on the ‘standard’ maxim receiver circuit in terms of both range and data rate. But building such an improved optical interface is a project in itself.
Does this help?
Marco
Many Thanx to Marco for the detailed documentation and to SOI_Sentinel for the explaination.
Actually, my teacher end up changes the project to a robotic arm, which is more related to the course topic (Industrial Automation).
Thanx a lot, this actually sparks my interest for underwater projects