My concept...

[unixslave]

I would like to share an idea I have had in the workshop in the past few months...

There are those who are using Arduino for control...

I am currently making a pressure housing for my Galaxy S android.

I intend on using one of my bouyancy tubes to contain some of my other sensors to connect via
bluetooth, so I do not have as many bulkhead connectors.

It's got a nice little fluxgate compass, marginal metal detection, autofocus camera...
Makes a nice datalogger, and I am adapting some command and control features for semi autonomous
operation.

[PaulC]

I am not sure, but I thought that somewhere on the net I read that bluetooth doesn't work under water. I think it was something to the effect that the water scatters the signal too much for reliability, but I might be wrong.

[unixslave]

Correct. But I believe that's for total communications.

I am proposing for communication distances of about 6" - 7"...

[SoakedinVancouver]

Can you elaborate on the "marginal metal detection"?

[unixslave]

I figure, that by using the flux-gate windings on the compass, and the loop in the antenna, I should be able to detect
changes in resonance thus detecting the presence of metals very nearby.

I surely am not talking the sensitivity and/or discretion of a true M.A.D.

[SoakedinVancouver]

What make/model of flux gate compass?

It might work, would you have the micro controller analyze the sudden jerking of the compass and decide on the nature of the input?

[unixslave]

Well...
I was going to use an HMC5843, pretty much the standard in most Androids, and gasp Iprones....however,
Honeywell decided to keep up to pace with technology and provide a more advanced chip... the HMC5883L...

The spec sheets say that they have figured out the proper level filtering of the earth's magnetic field,
and thus is able to offer a better discriminator. That, and they will be utilizing a 12-Bit DAC......

So even with those two small improvements, will yield a much higher resolution.

HMC5883L 3-Axis Compass IC magnetic sensor in a
3.0x3.0x0.9mm surface-mount 16-pin leadless chip carrier (LCC). The HMC5883L includes Honeywell’s
state-of-the-art, high-resolution magneto-resistive sensors with automatic degaussing (demagnetizing) strap
drivers, offset cancellation and a 12-bit ADC for high resolution earth field sensing.

This should be rather easy.. the Linux kernel has support for the HMC5843 (kernel 2.6.34+). so the libraries
should be close, if not workable or hackable into the config I desire.


Don't think that I am hooked on HMC's ... I figure any device w/ <=1mv/gauss that supports the
standard 2 wire, I2C spec 2.1 should be just fine.

[SoakedinVancouver]

OK, 'looks like you have a good handle on the sensor, and the interfacing, what about the physical mounting? Its own pressure chamber way up front so that it is away from the thrusters (noisy DC motors that they are...)?

Thanks for the details so far, you have a different concept than what I was planning for my future ('still on V1.0) version of a practical ROV. I was planning to mount a "standard" metal detector loop at the front, driven by a "standard" circuit. And I am worried about the thrusters...

[unixslave]

(noisy DC motors that they are...)?

Now, I hope that this does not indicate a change in the topic...

But the beauty is the simplicity. There will not be 'motors' plural.

I am thinking of using a single well insulated / shielded motor, and instead of using motors and propellers...

It will drive a small pump to provide the pressure to a water stream and I plan on controlling it's axes
by small poly tubes in much the same manner as a LapBelt does for the stomach, then control them
with a linear shape memory alloy actuator, AKA Muscle Wire. ALA, no noise when in operation.

They provide about 1.5 to 1.8 pounds of direct pulling force, which I should be able to control it's mechanical advantage.
If that fails, they make rotary wire actuators, and I will use them to move small plastic gate valves sending the water stream in which
ever of 3 axes I wish...


edit: actually, I just received an email from a manufacturer that claims 5 lbs/ft on direct pull actuators....

[unixslave]

Nice.

Update.... Got an evaluation board and the chip...

Nice.. I think I can handle the 1/3 oz in total weight.

GUI interfacing is promising. Weak on aesthetics, but loaded with functionality.

Hmmm.. I wonder.. if I get enough of these... mebbe make a sort of echo locater base unit...

Plant that on the seabed. Using a little time domain reflectometry with echo ranging, and headings,
combined with some nice algebra, I should be able to make autonomous DR based 'seeker' units.

I can see 6 or more of these little guys scurrying about looking for what I want...