Construction
1. Camera
For the purposes
of the FTACS, a digital camera was clearly the best option
due to storage convenience, relatively low cost, and feasibility
of internal modifications. Due to the nature of the circuitry
on the controlling board, a camera with a sliding on/off switch
was preferred over a momentary action switch. This requirement
limited the options available, but a suitable candidate was
easily found – the Panasonic Lumix LS3 (Fig. 4). It
features 8MP resolution, and had the added benefit of being
simple to disassemble (Fig. 5), which aided the modification
process. A 16GB SD card was installed in the camera, which
should hold 8000 photos at 5MP resolution.
Figure 4 - The brand
new Panasonic Lumix
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Figure 5 - The gutted
camera
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The locations of
the on/off switch and AF/Shutter switches were identified,
and thin gauge enamel wire was soldered onto the respective
copper pads (Fig. 6).
Figure 6- Soldering
onto the existing switches
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Figure 5 - The box
and fan
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The camera was
mounted in an IP65 rated waterproof enclosure (Fig. 7) with
a transparent lid to allow incoming light to the shutter.
As the installation site has little protection from solar
radiation, it frequently experiences temperatures above 35C.
As such, it was necessary to install an 80mm computer fan
(rated IP55) inside the box to provide cooling and ventilation.
Ventilation holes
were drilled into the back of the housing, along with mounting
brackets secured with pop rivets (Fig. 8). An 8 pin DIN socket
was also installed on the box (Fig. 9) to allow communication
between the camera and the controller board, which was to
be external.
Figure 8- Mounting
brackets
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Figure 9- The box in
its semi-completed state
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Fig. 10 shows the
semi-complete housing with wires from the modified camera
connected to the DIN socket. The completed camera box is shown
in Fig. 11, with an elastic band merely to hold the two halves
in place prior to installation of a waterproofing rubber gasket.
Figure 10 - Mounting
the camera inside
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Figure 11- The completed
camera and box
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2. Enclosure
The camera box itself was not deemed satisfactory protection,
as the ventilation holes meant that some water ingress would
be permitted during heavy rain, and thus the camera would
be subject to the elements. With this consideration in mind,
a heavy duty enclosure was designed both to reduce the internal
temperature and prevent water ingress. This enclosure was
developed from a humble looking waste paper bin from Bunnings
Warehouse. An opening slot for the camera shutter was cut
out of the plastic (Fig. 12), and right angle brackets were
fixed at all four corners of the base (Fig. 13).
Figure 12 - A humble
waste paper bin
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Figure 13- The bin
being slaughtered
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Brackets were also
fixed on both sides of the open slot (Fig. 14) in order to
mount a “roof” to further protect against heavy
rainfall. The “roof” was constructed using a rectangular
slab of 5mm fibre cement and was mounted at a slight slant
to prevent water inundation (Fig. 15).
Figure 14 - Stabilisation
and roof brackets
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Figure 15 - Sloping
fibre cement roof
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Finally, the entire
enclosure was wrapped in reflective aluminium roof foil to
protect the plastic enclosure from the damaging effects of
UV radiation. This foil was secured in place with heavy duty
aluminium tape (Fig. 16).
Figure 16- The completed
enclosure
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3. Controller
Board
The full circuit
diagram of the control board is shown in Fig. 17. The board
consists (from left to right) of a 555 timer configured to
operate at a frequency that will close the shutter every 15
minutes, a J/K flip flop IC which enables/disables the auto-focus
(AF), a NOR gate which selects the appropriate time to trigger
the shutter, and finally two relays with their respective
BC548 driving transistors and protection diodes. This is the
same circuit (and board) used in my time
lapse photography system.
Figure 17 - Schematic
diagram for the controller board
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The 555 timer IC
is wired in the regular astable mode, with the values of components
chosen such that the frequency is close to 1 per 7.5 min (or
~0.0022 Hz). The AF relay is toggled on and off via the flip
flop configured in toggle mode which operates on the rising
pulse. Some straightforward logic via the NOR gate ensures
that the shutter is operated only when the camera is focused
– that is, on the falling edge of the clock signal.
The associated timing diagram is provided in Fig. 18.
Figure 18- The associated
relay activation timing diagram
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The completed board
was constructed on strip board (Fig. 19) after initial testing
on a breadboard was successful. The relays chosen had a maximum
contact current rating of 3A, which proved to be huge overkill
for the switching of such small signals. As such, they drew
a lot more current when operational than would be necessary
otherwise. However their relatively low cost was an advantage,
and should prove to be fairly robust in the field.
Figure 19 - The completed
controller board
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Figure 20 - Voltage
regulator slave board
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The voltage regulator
supplies 5.1V to the camera DC input, thereby bypassing the
camera’s internal battery but at the same time keeping
it charged so that the date and time settings inside the camera
would be preserved. This was constructed using an LD1117V
low dropout regulator; although a standard LM317 variable
voltage regulator would have sufficed. This part of the circuit
was also constructed on strip board (Fig. 20).
Circuitry for the
water sensor was mounted on the same board as the two circuits
above (Fig. 21). This was built from a modified “kit”;
the design consists simply of two water probes which trigger
a DPDT relay via a Darlington transistor. The rest of the
circuitry on the board is wired through this relay such that
no components will be powered when the ground is dry.
Figure 21 - Completed
board with water sensor unit
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Figure 22 - Battery
to be used in the field
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Power for the FTACS
is sourced from a 12V, 17.2Ah battery (Fig. 22). The 9V battery
is for an indication of scale only, and is not present in
the final installation.
4. Water
probes
A crucial element
of the FTACS involves the actual sensing of the water level
itself. In essence, the entire system needs to be switched
on only when the water level rises above ground. To do this,
the circuitry described previously was employed. The probes
itself, however, need to be mounted at ground level rather
than at the observation box (which is about 6m above ground
level) with the other components of the system.
The probes themselves were constructed out of two stainless
steel rivets which were each secured in a watertight cable
grommet and connected to a naked strip terminal at the other
end (Fig. 23). These grommets were then mounted in an IP65
rated ABS box, and connected to a 15m length of twin-core
power cable (Fig. 24).
Figure 23 - SS rivets
used as water probes
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Figure 24 - The water
probe box with lid off
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The cable was threaded
through a third cable grommet and waterproofed by adding a
couple of layers of heat shrink tubing (Fig. 25). The probe
box was completed after inserting the waterproofing rubber
gasket. The completed probe box (Fig. 26) is capable of withstanding
long term submersion underwater.
Figure 25 - Watertight
cable relief
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Figure 26 - Completed
water probe box
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