The key to the success of this project was the sensor technology.
Various sensors were considered including pressure mats, ultrasonics,
microwave doppler radar and several optical methods. It was
decided to use a retro-reflective optical sensor.
This was easy to set up and verify its operation in the field.
It had the advantage over other optical methods of positive
operation resulting from the target breaking a light beam while
only requiring wiring to one side of the penguins path. It was
decided that this should be a commercially available part as
there was insufficient time to develop a reliable device. The
sensor finally selected proved to be very reliable on the test
bench and was extremely difficult to fool into false triggering.
It was encased in a small metal box and environmentally sealed
to IP67 (it being intended for wash-down in industrial applications).
It was decided to provide the sensor with a protective hood.
Although not strictly necessary this could provide extra protection
from the elements, shielding from ambient light and vandalism
from the penguins. The hood would also provide a method of fixing
the sensor on location and a means of adjusting the alignment.
Because the final location was to be on a cliff top it would
be subjected to salt spray, thus the whole assembly was designed
in stainless steel.
Design of the Counter
With the sensor issue resolved we started design of the main
counter. This was fairly straight forward and conventional.
Power was derived from a vehicle battery, provision was made
for either 12V or 24V operation. This battery supply was conditioned
to ensure its quality before being applied to the main counting
electronics or output to the sensor assembly. The counter electronics
was also provided with a back-up battery to protect the count
should the main battery be
accidentally disconnected. In fact, this back-up battery could
power the counter for several years operation providing the
sensors derived their own power from a separate supply.
The input from the sensor was buffered and conditioned to limit
the counter's speed of reaction. This was to minimize false
triggering while still being able to count the fastest penguins.
This buffering also protected against over voltage inputs in
excess of 50V.
During the design it became apparent that a two-channel unit
would add little to the cost of the manufacture, we offered
this to the customer as an option, which they subsequently took
All the electronics were designed to operate down to -10°C
and enclosed in a portable enclosure sealed to IP54. The external
connectors were rated to IP68 and provided with sealing caps
to protect them when not in use.
By this time Ian Strange had returned to the Falklands, so
we sent him information on the design and a preview of the finished
unit via the Internet. Once we were in agreement that the basic
design was as envisaged at the start of the project we proceeded