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 up.

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 to production.