[PSUBS-MAILIST] Compass Choice

[Jon Wallace]

Hi Alan,

I'm not aware of any Plug'n'Play modules like that.  The closest thing would be the unit that Cliff Redus uses in his sub.  Once you have the framework in place you can add sensors that "plug in" and communicate with the main processor all using the same protocol.  However, I don't know if there are sensors for everything that a cert authority would require and it's a relatively expensive setup compared to combinations of sensors from other manufacturers.

For any modern PC or MAC you would need to have serial communication for all devices which you could then display via a custom Java app or VisualBasic or even a perl script that displayed info via HTML using custom graphics.  The problem is most small individual sensors such as temp, pressure, etc use either an ADC or a protocol like I2C or SPI to communicate with the processor.  Even most O2 and CO2 sensors use these methods although more expensive models do have a serial option.  However, getting every sensor you need to output in serial is probably not going to happen.

Then you have the issue of condensation and other water infiltration destroying the electronic components, hence Alec's route of simplifying his next sub with analog vs electronic.  Replacing a notebook or laptop is still going to be a multi-hundred dollar event.  Replacing a small microprocessor is going to be about $30 (US).  So you don't get the fancy graphics with a microprocessor but you get adequate information display with cheap replacement costs.

My current project takes a pseudo-PNP approach in that it is comprised of individual sensor modules that plug into the microprocessor.  If any sensor fails you disconnect it from the processor module and replace only that sensor.  If the processor fails, disconnect all the sensors, replace the microprocessor module, and plug all the sensors back in.  Display is on 7-segment LED and character cell LCD, so is not fancy, but is functional.  I will also be able to log all sensor data to an SD card for post dive analysis which can of course be as graphical fancy as I choose.  And of course MATILDA will provide voice alarm capability.

As with everything, compromise reigns.  I started out looking for a PNP PC based solution but eventually gravitated to a microprocessor due to cost, availability, and convenience.  A certified sub budget will get you a PNP solution, but my recreational budget won't get me there.

We can likely come up with a microprocessor solution that complies with GL or ABS although my personal project won't comply with it, limited to water pressure (and depth), vertical rate of movement (feet per minute), water temp, cabin temp, cabin pressure, cabin humidity, O2, CO2, and various MATILDA voice alarms.  However, it's merely a matter of identifying the required sensors that have the capability to satisfy the cert authority's specifications.

Jon


-------- Original Message --------
Subject:	Re: [PSUBS-MAILIST] Compass Choice
Date:	Tue, 14 Jan 2014 16:03:01 -0800 (PST)
From:	Alan James <alanlindsayjames at yahoo.com>
Reply-To:	Personal Submersibles General Discussion <personal_submersibles at psubs.org>
To:	Personal Submersibles General Discussion <personal_submersibles at psubs.org>

Hi Jon,
it doesn't look like it does what I thought it did.
The software provided seems to be just a demo.
I was hoping it was something I could plug in & voila, I had graphics
of a compass on a screen.
G.L. seems to require a duplication of a lot of the monitoring equipment
as well as alarms for everything, so I'll continue going through the manual 
till I know exactly what I need, then look at my options.
Perhaps we could develop a G.L. & ABS compliant module as a Psubs
 group project???
It could monitor battery levels & amp draw, ballast levels, control & monitor 
the O2 delivery system & CO2 levels, incorporate the digital compass &
display cabin pressure etc.
Alan