Issue
162 January 2004
Remote
Observation Station
by
Richard Dreher
Richard’s
Remote Observation Station is a nature lover’s dream.
It allows you to watch wildlife on a TV from more
than a mile away. At the heart of this inexpensive
solar-powered system is an HC08-based photovoltaic
charge controller.
Start
•
PVCC
Control Board
• Firmware
• Configuration
Software
• Future
Enhancements •
Sources
and PDF
When
my wife and I visit my in-laws, who live in northern
Wisconsin, we often hear tales about the wildlife on
their mostly wooded, 300-acre hobby farm. Stories of
black bears with cubs, timber wolves, and rare albino
whitetail deer are often told. Yet, try as I might,
I had never seen any of the animals for myself, except
at extreme distances. Because simply walking into the
woods to get a better look would scare the animals away,
I needed a way to remotely obtain a close-up view of
them. So, I went in search of a solution that would
either provide my wife and me with great views of the
indigenous wildlife or prove that the stories were of
the fish variety. My solution was the Remote Observation
Station (see Photo 1).
|
(Click
here to enlarge)
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Photo
1—I completed the first test station in late summer.
The solar panel is fixed facing due south. The panel’s
angle at this time of year is approximately equal
to the station’s latitude. |
The
station needed to be relatively inexpensive, easy to
use, and easy to maintain. It couldn’t rely on utility
power (it would be in the woods after all), and it couldn’t
require frequent trips to retrieve the battery for recharging.
Solar power seemed like a logical solution. Given that
it would be solar-powered, the power supply components
would have to handle the wide voltage swings possible
in solar-powered systems. I wanted a charge controller
to prevent overcharging the battery. I also wanted an
easy way to see if the battery was recharging successfully
without having to make a trip to the remote station.
It was this last requirement that led me to design a
custom piece of hardware instead of buying an existing
battery charge controller.
To
come to the point, I wanted a system that would need
as little maintenance as possible, and would alert me
when trouble was ahead. Finally, I wanted to be able
to turn on a TV to watch the wildlife without any other
special receiving equipment, except possibly a high-gain
antenna.
The
station’s control board, which is called the photovoltaic
charge controller (PVCC), prevents the battery from
becoming overcharged and over-discharged. It also provides
feedback about the battery’s state. Anticipating that
the station would be miles away and already transmitting
NTSC video, it seemed natural to simply overlay system
performance information on the video signal that shows
up as characters at the bottom of the TV screen. In
other words, an on-screen display (OSD).
To
meet my objectives, I chose a microcontroller-based
design, which significantly increased flexibility without
adding to the overall hardware complexity. To further
reduce the cost of the project, I decided to forego
a traditional user interface made of buttons, switches,
and LCDs. Instead, I wrote a configuration program for
Windows that configures the PVCC behavior via a serial
connection. Any change to the configuration data is
stored through power cycles in a 64-byte block of the
program flash memory. The microcontroller also allows
me to fine-tune features with little or no change to
the product’s basic hardware design.
SYSTEM
OVERVIEW
The
Remote Observation Station integrates six main components:
a CCD video camera, a PV solar panel, a rechargeable
battery, a temperature sensor, an RF video transmitter,
and the PVCC (see Figure 1). The control board, which
is based on Motorola’s MC68HC908QY4 microcontroller,
sits at the center of the system; it provides a charge
controller, high-efficiency power regulators, a video
sync separator, and an RS-232 serial interface. Photo
2 shows the heart of the Remote Observation Station
enclosed in an aluminum box.
|
(Click
here to enlarge)
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Photo
2—For outdoor projects, I found this watertight,
power-coated aluminum case by Rolec to be excellent. |
The
PVCC board provides a simple on/off battery charger
using the PV solar panel as a power source. The control
board adds battery state information in the form of
a text overlay to the video signal generated by the
camera. A PC can be connected to the control board via
DB9 connector J1 (see Figure 2).
|
(Click
here to enlarge)
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Figure
2—Port pin PTA0/ADx serves a dual purpose; it is
used as the serial I/O port in Configuration mode
and the daylight sensor in Charge mode. |
The
video transmitter operates in the 433-MHz amateur television
(ATV) 70-cm band. The transmitter is a Video-Lynx Model
Z70A designed by Ravi Goonasekeram (sign KA3NNJ); it
has a rated output of 50 to 100 mW while using approximately
300 mA at 10 V. I chose this transmitter because it
provides a clean, stable signal, and it operates on
a frequency that corresponds to a specific channel on
a cable-ready TV set. Actually, one of four stations
can be selected with a DIP switch. You can also send
a test pattern directly from the transmitter to aid
in the initial setup.
Currently,
the station is located 1.5 miles from the receiver.
It transmits through a quarter mile of trees. In order
to span that distance with such low power, I needed
a high-gain antenna. I built a 15-element Quagi, designed
by Wayne Overbeck (sign N6NB), for the 70-cm band. This
antenna provides a gain of approximately 15 dBd. Fortunately,
the antenna is made mostly of wood, so it was inexpensive
to build.
A
12-V valve-regulated lead acid (VRLA) battery powers
the system. The HC08 microcontroller’s integrated 8-bit
A/D converter monitors the battery to determine the
charge state. The battery’s temperature is monitored
using a Dallas DS1820 1-Wire temperature sensor, which
is interfaced to the microcontroller through a single
I/O pin and some software bit banging to instruct the
microcontroller to behave as a 1-Wire master.
