Numeric Data on Hog Island

Readers of these diaries may have noticed something missing from the Oyster LTER diaries: although we have provided connectivity for laptop PC's, webcams, and even videoconferencing capability, there were no examples of gathering traditional numeric data from in-situ sensors as had been modeled over the previous several years by PI Dave Hughes. This trip was made to correct that omission.

We decided to connect a meteorological ("met") site near Machipongo
Station at the north end of Hog Island. Click on this link for a quicktime panoramic view of the site (prior to our modifications).

Campbell Versus Orinoco

Since Hog Island has an 802.11b network, we sought an alternative to
the Campbell NL-100, the Ethernet-to-CSIO converter which we had used for bridging between the Internet and the wireless networks in Alaska and Wisconsin. (CSIO is Campbell's proprietary variation on an RS232 serial port, allowing Campbell to do some neat tricks such as sharing power with other modules.) Had we used the NL-100 on Hog Island we would still need a separate radio, resulting in high costs. Our aim this time was to convert a CSIO (serial) connection directly to
802.11b radio at the met station.

Most "solutions" to serial-over-802.11b are kludges, consisting of a
single port terminal server (which converts serial to Ethernet)
connected to a separate Ethernet-to-802.11b converter, selling for
the combined cost of the two modules plus an extra 50% for the "added value." Orinoco, on the other hand, offered a single unit (the
EC-S that combines both functions, and at a significantly
lower cost than the competition. The EC-S has a DCE serial
connection, meaning it is designed to connect to a PC or laptop (or
other DTE equipment) using a straight-through DB9 serial cable.
Although not important to this application, the EC-S also sports an
Ethernet jack.

We have recently learned that 3com sells a similar (or possibly
identical) unit to the Orinoco EC-S, called the "Ethernet Client
Bridge." It may be available at a lower price. For
serial-to-802.11b connections, either one is a bargain.

The EC-S, like many 802.11b devices, is shipped without a
radio. The radio -- a standard PCMCIA 802.11b card like you would put
into a laptop computer -- is bought separately. The reason for this
is either to allow the user to pick the quality/security/power options
appropriate for the job, or perhaps it is just to make the price look
lower; take your pick. In any event, we chose the Lucent Silver
card, which cost a bit less than $100 at this writing, to go into the
$300 EC-S, for a total cost of $400.

We connected the EC-S to a Campbell data logger via Campbell's SC929 cable, which is designed to provide a direct connection between a laptop or other PC and a Campbell CSIO port. Since the SC929's PC end has DCE wiring (to connect to the PC's DTE serial port), we put a Null Modem adaptor between the serial end of the Campbell cable and the Orinoco EC-S unit.

Connector diagram for CSIO-to-EC-S link. M and F denote
DB-9 connector genders.

We used a 14 dBi Comtelco panel antenna, about 8" square. We
connected it to the EC-S using an Orinoco-to-type-N "pigtail" adaptor
plus about a 2 meter length of LMR-400 cable. (For such a short run,
LMR-240 would have worked fine as well.) That antenna, with clear
line of sight, had reached 10 kilometers from Machipongo Station to
Broadwater Tower. In this case we were punching through a thicket to
reach Machipongo, but the distance was short (less than 1 km), and
still provided a reliable link.

Power-related setback

As will be discussed in the next diary, power consumption and
conversion is a major issue.

In an effort to conserve power, we tried DC-to-DC conversion. This
was initially a little intimidating because the EC-S power supply
converts 120 volts AC to 5.2 volts DC. It's pretty easy to find a
12-to-6 volt converter, same for 12-to-4.5 volt; but 12-5.2 volt was
not to be found at the local Radio Shack. A call to the ECS's
manufacturer was encouraging: they told us that the unit could run on
either 6 volts or 4.5. We went with a 6 volt adaptor, in the hope
that higher voltage and lower current draw would be the most
efficient.

Although it worked fine in the lab, it would not work in the field.
The power light glowed red, indicating power problems.

We took the unit back to Machipongo Station and tried several
variations, including substitution of a 4.5 volt DC-to-DC power supply
for the 6 volt one. The use of a 6 volt power supply was questionable
in retrospect, as real batteries in the field often run at over 13
volts, pushing that adaptor's output to 6.5 or even 6.7 volts, which
is a bit farther from 5.2 than we liked.

Back in Machipongo Station the unit functioned normally until we
connected the Campbell SC929 cable, at which point the EC-S power LED went red. The only power source that worked with the Campbell cable was the original 120 volt AC-to-5.2 volt DC adaptor, which required the use of an inverter.

With the new inverter-plus-power-supply arrangement, the installation
was successful. From anywhere on the Internet, it was now possible to
access the Machipongo meteorological station. The weapon of choice
for that activity has been Campbell's PC208W software which, though
designed for use with an NL-100, worked fine with the EC-S.

Screen Shot of PC208W Software Viewing Hog Island Met Station

-Tom Williams
Special Assistant
NSF Wireless Field Tests

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