RTC controlled buoy

[geirandersen]

A problem with having scientific equipment on location over a period of time is the chance of it being stolen. This equipment can be very expensive (not my DIY stuff, but real quality loggers), a logger can easily cost in the range of several thousand dollars.  One way to avoid this would be to have the buoy hidden until it was time to retrieve the logger.

My first thought was to have some sort of sonar signal to trigger the buoy to surface. As this turned out to be a rater complicated system, I settled for the next best thing of having it time based.

At the heart of this system there is a small PCB with a DS1337S+ Real Time Clock. It has its own coin cell battery (on the bottom of the PCB) and a supporting MOSFET circuit to turn on/off the power.
There is no microcontroller, only the RTC. So the alarm is a one shot deal, but what we need for this purpose.

The second part is a CO2 bicycle pump. As the 16g CO2 cartridge only yields about 10 liter of volume we blow the whole cartridge every time.

The valve is opened by a geared down 6V motor at 60 RPM. As the valve only needs to be opened enough to let the CO2 flow the motor will only run for 1 second. There is no H-bridge to reverse the motor so it has to be turned back manually.
The power source for the motor is a 7.4V LiPo battery, and as it is only run for 1 second each time it can last a long time.

To set the alarm I’m working on a Windows application letting you select the date, time and ‘puls’ of the motor. This will work in conjunction with an Arduino to set the RTC over I2C.
(the time set in the video is hardcoded 3 minutes from now)

The second problem was how to mount the controls in a waterproof environment and what balloon/buoy to blow?
Then I came across something called a dry bag that is used by people involved in kayaking and canoeing. This fit my purpose very vel. Here I could blow the whole cartridge in the same environment that hosted the electronics. I would probably add an extra zip-lock bag around the electronics in the full scale test, but the principle is sound.

The system is a modern version of the ‘salt idea’ from Once Upon a Time in America

But this is probably a reference for the older members of LMR

https://www.youtube.com/watch?v=wT5rGP36kQk

[christhecarpenter]

Mr. Andersen…

You are the undesputed KING of pratical uses of robot-brains…

I can’t tell you how many times I have used your work as a reference when trying to explain to people what you can do with an Arduino and a few parts. --This one is just as awesome as the rest, my friend.

[lumi]

Very smart approach. Why do

Very smart approach. Why do you release all the CO2 and not close the valve when the buoy rises?

@OddBot: I believe that those cartridges are for one time usage. You can bring them back to re-fill them, but not doing it by yourselves.

[roman505]

If it were me, lumi, I would

If it were me, lumi, I would not risk loss of a scientific instrument through insufficient gas in an uncalibrated container, hence refill each time. Blowing the lot also may help to get it up if it is resting on the bottom with anything weighing or snagging on it.

This is only the second time I have seen your work, Geir. Love it. Interesting problems, simple solutions.

[leroy2007]

I don’t know in what

I don’t know in what timeframe you’re looking for to blow the cartridge. But when your sensor array is in changing enviromental conditions for weeks or months at a time, it might be worth considering the DS3231SN for its temperature compensated time-keeping.

A 1337 (and 1307) are prone to go out of sync very fast in changing enviromental conditions, leading to a premature or late activation of the cartridge.

You might want to look into a diver lift bag 

 

as your “balloon”. It is important to note tha from whatever depth you’re activating your cartridge, air expans rapidly on its way to the surface, blowing up a balloon if it isn’t fitted with an open end or pressure release valve of some sorts.

[geirandersen]

Thank you for your comment

Thank you for your comment Leroy. The timing is not all that crucial. If the buoy is released within +/- one hour then it is good enough for me.