Specifications

2
Some of these constrains were that the stations should be capable of operating both during the
day and the night, that the stations should be mobile, and that the station should be weather
resistant and capable of running across a wide range of temperatures. Furthermore, we focused
on making the production process scalable; thus, we used only commonly available parts that
could be easily assembled with minimal work where possible. We also have focused on a
modular approach that utilizes components that are easily swappable to allow for easy repair or
replacement.
2.2 Prototype Design
Given that no known consumer–grade solution is available for recording one week of video, we
relied upon the use of a general purpose computer. To minimize power constraints, we needed a
computer that was designed for minimal power consumption. While using a laptop was a
possibility, laptops are relatively expensive, not sufficiently customizable, and include features
not necessarily relevant to the current application. Therefore we went with a specialized
motherboard and central processing unit (CPU) designed for low-power embedded applications.
The motherboard comes with a high-efficiency DC to DC converter designed to regulate voltage
and current supplied to the motherboard when powered by a 12-volt battery, as is typical in
automotive applications. The CPU and power supply are both fanless and do not require active
venting.
While the majority of embedded systems available today utilize specialized architectures, this
motherboard and CPU are compatible with the x86 architecture. This minimizes the amount of
specialized software required for development of applications using this hardware and enables
the use of the open-source operating system Linux. Linux is highly customizable and can be
configured to run in a low power consumption mode. While some specialized software was
written in C to manage the video capture, memory buffering, and file writing operations, the
video capture card drivers were open source.
In order to record one week of video with a reasonable video compression rate, a 250 gigabyte
hard drive is required. A standard desktop computer hard drive was selected in combination with
a swappable hard drive system such that the digital video could easily be removed from the
recording station and inserted into another computer for data analysis. Although a laptop hard
drive is designed to consume less power than a desktop hard drive, the cost is significantly
greater. The operating system software can be customized to minimize the power consumption
of the hard drive by caching video in memory and spinning down the hard drive in between
writes from memory. The hard drive has all software preloaded such that the computer boots
from the hard drive and immediately begins recording video.
Analog, rather than digital, cameras were chosen as the most appropriate solution to capture
video. They are low power, low cost, ruggedized, and the camera that we selected is pre-
equipped with infrared light-emitting diodes for active illumination of the scene at night. An
analog to digital video capture card is required for use of this camera. The capture card converts
the video into a MPEG compressed format using a specialized digital signal processor, thus
minimizing the processing load and power consumption of the CPU.