LITTLE BUOYS, LITTLE
RADIOS
As part of the summer lake studies
of the LTER at Trout Lake, smaller buoys are put out on the water
in various lakes, each with a specialized sensor unit, and one CR10X
data logger.
Routinely these deployments require
someone to launch a boat every time it was desirable to fetch the
data - at least weekly - and go out to retrieve a memory module,
replace it with an empty one, and come ashore. This in turn required
usually two people driving the vehicle and handling the power boat
launches and recoveries. Here is a typical 'small buoy' before launching.
In the week before my trip to the
Trout Lake Station, Paul Hanson and his student assistants had successfully
experimented with using a pair of FreeWave DRG115 data radios. One
was placed in the instrument box of the small buoy, connected to
the serial port of the CR10X data logger, and the other was operated
from a laptop computer on shore. The data from the one small buoy
was fetched satisfactorily.
But it became instantly clear that
it would require one $1,250 FreeWave radio for each deployed buoy,
and one one shore, and perhaps one spare. For four buoys on the
water at once, that would amount to at least $7,500. A stiff price
for radios that were only needed to move data at 9,600 baud, though
they were capable of 115 Kbps, across up to one half mile of water,
while the Freewaves could reach many miles. And being 1 watt radios
they needed up to 500 milliamps from the battery on the buoy.
So I was asked whether there was
a cheaper solution. I was ready with a pair of World Wireless Microhoppers,
that cost, in OEM configuration, only $300 apiece, could operate
at 19.2Kbps, and only used 100 milliwatts for communications.
These were the same radios I tested
in the Luquillo Rain Forest, Puerto Rican LTER, going 600 meters
through jungle vegetation.
Here is a pair of them, with a small
12 volt battery which can operate them for a time, sitting on top
of a Wi-Lan Hopper Radio Case that does the same thing.
As time was running short on our
visit, we bench tested them using a small buoy that was being readied
for deployment on one of the lakes.
In this case one must run World
Wireless Microhopper software on a laptop under Windows to see whether
you have a signal and how strong it is. There are no status lights
on the radio itself - to save power.
We put one radio in the case, took
off 12volts from the data logger battery, got a connection, and,
by running PC208 software on the PC, were able to access the data
coming out of the logger. Hanson and his assistant were pleased.
I promised to get him 6 such radios, with custom cases, so he could
try them out on 4 separate small buoys.
Here is Matt Van de Borgert holding
the small Microhopper that is connecting to a like radio and computer
across the lab.
This type radio ALSO might be a
partial solution to the problem of multiple radios on data loggers,
and only one radio on shore, running PC208W Campbell software. In
the configuration choices for the Microhoppers, the software can
instruct the Microhopper to be one of over 100 'Code' sets. A series
of 5, 10, 100 data loggers, connected to a Microhopper, could each
be configured with a separate Code number - one to each radio. Then,
when the data collector person on the shore wants to access a specific
logger, he sets his OWN Microhopper to the Code of the radio/data
logger he wishes to access, and the radio will only talk to that
one radio, and thus to only one - the target - data logger.
This requires manual changes for
each access, but, because the small buoys are deployed on more distant
lakes - up to 20, 30 miles away from the Trout Lake Station, they
need to be visited anyway by car or truck, to the nearest shore.
So switching the radios is an easy task.
We found, as we had learned about
in bench tests at World Wireless near Seattle, that we had to put
in 150 milliseconds of delay into the PC208W software, to maintain
a reliable connection. With no delays (default software condition),
or 50ms, resulted in intermittent connectivity.
They would easily reach across the
water a half mile. They needed to be put in small watersealed cases,
but it sounded like the ideal solution that WOULD scale across many
buoys.
These Microhoppers, by this experiment,
have now proven useful, scalable, and economic for the multiple
buoy problem in Wisconsin, and the light sensor problem in Puerto
Rico. We have a hunch they will also work in Alaska to connect up
multiple data loggers. The only question is how much effective range
can we get out of them, using larger external antennas.
