Panthera Camera Trap 5/10/2012
Panthera Camera Trap
5/10/2012
Basics
The Panthera camera trap was designed specifically as a wildlife research tool combining low cost, ruggedness,
low weight, long battery life, and sufficient picture quality for individual animal identification, particularly
tigers. Imaging is digital but without the delays that are common with low cost digital cameras. Figure 1 shows
a front view of the camera trap. About the size of a typical paperback book, it is 18.5 cm high, 11 cm wide, 4.5
cm thick and weighs 530 grams when fully loaded with batteries. There are upper and lower sets of slots for
straps and a groove across the front face for cable mounting. The overhang above the camera window helps
keep the window dry in light rain and often suppresses morning dew formation as well. The camera itself is a
square module about 1cm on a side and can be seen in the center of the lower rectangular window. The dark
circular window above the camera module is a Fresnel lens used with the passive infrared motion sensor. The
rectangular window just above the center is the xenon flash. The power switch is on the bottom left, and next to
it is the USB port. These two weatherproof connections are the only user interface needed for normal operation.
Access to the interior battery and desiccant compartment is via a screw-on cover sealed with an o-ring.
Figure 1. A front view of the Panthera
camera trap.
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Hardware Description
Batteries
Figure 2 - Battery compartment.. The battery compartment is accessed by
removing the 6 screws on the back cover. The figure shows the three possible
battery configurations that can be used. The batteries are arranged as two sets
of 3 in parallel. The camera may be operated with 3 batteries in either of the two
configurations on the left or with a full set of 6 batteries as shown on the right
The lifetime of batteries varies with operating temperature, with low temperatures shortening the life,
especially for alkalines. As a rough guide, 3 alkalines will last about 23 days while 6 will provide
about 48 days. Low self discharge NIMH rechargeable cells last about 21 days for a set of 3 and 44
days for a set of 6. If operating in a cold climate (sub freezing temperatures) or if maximum battery
life is required, it’s best to use Lithium primary cells. In one test using a set of 6 Energizer Lithium
cells, the camera operated for 72 days.
The battery voltage is monitored by the processor and the camera will shut down when the combined
voltage of the cells falls below a specified value. A message regarding this is recorded in a log file
stored on the memory card (described below) along with the time and date so the period of inactivity of
the camera can be determined.
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Desiccant
Figure 3 – Desiccant compartment.
A rectangular opening above the
batteries is the desiccant
compartment which fits two 5 gram
desiccant bags.
Condensation of water on the inside of the camera reduces battery life due to electrical shorting on the
circuit card and can lead to corrosion which dramatically shortens the working life of the camera. The
camera seals are designed to prevent liquid water from entering the camera but water vapor in humid
air cannot be excluded so desiccant is required to keep the interior dry.
Field tests show that the two 5 gram bags of desiccant will be effective at preventing condensation for
two months in a warm humid environment. This exceeds the typical battery life so it is convenient to
just replace the desiccant each time the batteries are replaced.
Camera Module
A commercially available CMOS camera used in portable electronic devices like smart phones and
tablet computers provides all of the imaging function in a small, inexpensive, low power device. These
are available as a module with an integrated fixed focus lens that plugs into a socket soldered to the
main circuit board. These system-on-chip cameras include sophisticated image processing capability
including automatic exposure, color balance, and jpeg image compression that minimizes the need for
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data manipulation by the main processor. To meet the ultra low power requirements of the portable
electronics market, the device incorporates a standby mode which draws extremely low battery current.
Importantly, the delay from standby to full power image acquisition is only about 1/100th of a second
so fast moving animals will not be missed.
The main processor can issue high level programming commands that cause the camera module to
automatically set the photographic parameters such as exposure time, light sensor gains, and color
balance values based on real time conditions. Exposure and color balance involve proprietary
algorithms provided by the sensor manufacturer and are very effective. However, the processes are
iterative and require fairly long times to settle on the proper values, as much as several seconds in some
cases. This is too long to wait when capturing images so these adjustments cannot be performed with
each triggering event. The solution is to use a simple CdS light sensor (just to the right of the camera
module in Figure 1) to monitor general light levels and command the camera module to perform an
automatic exposure and color balance whenever the lighting changes by more than a preset amount.
The settings are saved and are ready for immediate use when a trigger occurs. This allows full use of
the excellent algorithms provided by the camera manufacturer which are much better than relying on
the general light sensor reading itself without adding any delay from trigger to capture. Of course,
captures cannot be obtained during the times when the camera module is busy, but with a reasonable
choice of lighting change condition, +/- 30% for example, the fractional dead time is typically only
1/1000.
A very important criterion for wildlife research, particularly for the tiger census work that motivated
the development of this camera trap, is the ability to identify individual animals by their markings.
This requires short exposure times to minimize motion blur so the exposure time adjustments made by
the camera module are restricted to allow only exposure times of 1/75 second or less. In the event that
proper exposure would require a longer time, the camera switches to flash mode. With the xenon flash,
exposure is just a few thousandths of a second so low light and night images are always crisp.
Good image quality also requires proper focus. The integrated lens in this camera is a fixed focus type
that gives sharp images from just a few feet out to infinity without requiring time consuming focus
adjustment.
Image resolution is important but need not be exceptionally high to meet the needs of wildlife research.
The megapixel count that is popular in marketing digital cameras is not a good metric for image quality
for several reasons. Perhaps the biggest reason is that high pixel counts in inexpensive sensors are
achieved via advances in lithographic reduction of the circuitry which cuts the pixel size but also cuts
the amount of light that gets captured within the tightly constrained exposure time that is available.
This trend has led to a reduction in the signal to noise ratio which manifests itself as noisy images
during low light conditions before switching to flash mode. Another reason to avoid stretching the
limits of high pixel count is that affordable lenses can’t focus sharply enough to take advantage of the
extremely small sensor sizes. Finally, high pixel count translates directly into large image file sizes
which reduces memory card capacity and increases data transfer times. The sensor in this camera
provides 3 megapixel images which strikes a reasonable balance among the various requirements. The
level of jpeg compression is adjustable to allow the user to trade off compressed image quality against
file size.
Motion Detector
A passive infrared sensor is used to detect when an animal passes in front of the camera. The
PYD1998 digital pyroelectric sensor from Perkin Elmer is sampled about 70 times per second. This
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high sample rate combined with the very short camera delay allows fast moving animals to be imaged
easily. However, a very short delay causes problems with slow moving animals since they need time to
reach the center of the frame. Therefore, a novel algorithm is applied to the sequence of sampled
sensor readings to trigger the camera module and capture an image when the animal is approximately
centered in the field of view regardless of the animal speed.
The motion detector includes a Fresnel lens to focus the infrared emission from a central area of the
field of view thereby extending the range of sensitivity to greater distances. The triggering sensitivity
can be adjusted by the user to suit the particular application.
Flash
A xenon flash is used for low light and night imaging. This provides brilliant color images with an
extremely short exposure time which completely eliminates motion blur. The flash circuit includes a
high energy capacitor that can be charged in about 15 seconds. It is kept fully charged while waiting
for motion so the flash can be fired without delay. With flash illumination, nearby objects appear much
brighter than those further away. This can lead to over exposed images for close animals and under
exposed images for those further away. To account for this, the user can choose among various
brightness settings that are appropriate for the expected target distance. In trail settings, this would be
the distance from the mounting tree to the center of the trail. The image brightness is adjusted using the
electronic gain of the camera module rather than changing the light emitted by the flash itself.
Microcontroller and Miscellaneous Electronics
The processor that controls high level camera trap functions is an Atmel microcontroller that features
an extremely low power mode of operation that is used while sampling the motion detector. Low
power while waiting for motion is critical to achieving long battery life. The Atmel device provides
several channels of analog to digital conversion along with digital input/output lines, and integrates a
variety of standard bus interfaces like the Multimedia Card Interface used for the Secure Digital (SD)
memory card, Universal Serial Bus for the external digital interface, Two Wire Interface for controlling
the camera module, real-time clock, and temperature sensor, and Image Sensor Interface for the image
data from the camera module. The real time clock chip provides date and time information that is
recorded with each image. It uses a coin cell battery to maintain timing when the main batteries are not
present. The digital temperature sensor chip records the internal camera temperature which is saved at
regular intervals in a log file as well as in each captured image. An inexpensive piezoelectric buzzer is
driven with a digital output line and provides an audible signal for various purposes such as indicating
a low battery condition on power up. There are 4 dual color LED indicator lights driven by the
microcontroller that are used to provide visual indications of various states of the camera as described
below.
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Figure 4. This shows a close up of the main
camera window. Each LED can be either red or
green or off.
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Camera Operation
LED Indicators
Power-On Sequence
The following power on sequence will be observed when starting with no USB device inserted.
All 4 LEDs will glow very dimly for about a second after the button is pushed. The microcontroller is
initializing during this time.
Next, the top two LEDs will glow bright red for 8 seconds. The microcontroller is performing tests and
checking for the presence of a USB device during this time. There will be an audible beep for the first
second as an indication that the processor has started.
After the top two LEDs turn off, a number of green LEDs will come on for about 1 second as an
indicator of remaining battery life.
4 LEDs on means there is >=80% remaining life.
3 LEDs on = 60-80%
2 LEDs on = 40-60%
1 LED on = 20-40%
0 LED on = <20%
There is an audible alarm indication of varying pitch lasting several seconds whenever the <20%
condition is detected. This serves as a reminder that the batteries need replacing soon.
Following the battery indication, the upper right LED glows red for about 2 seconds as the camera
performs an initial exposure adjustment.
Now the lower left LED will come on red (the other 3 are off). This indicates flash capacitor charging
and will last about 15 seconds. As the flash batteries get weak, this charge time gets longer. The red
LED will start to blink during the last few seconds of the charge up if the batteries need replacement.
After the charging LED turns off, there is a blank period of about 2 seconds followed by a brief green
flash of the upper left and lower right LEDs. This signals that the camera is ready to capture images
once motion is detected.
Auto Expose Sequence
Depending on lighting conditions, there may be another exposure adjustment required right away and
the upper right LED will glow red again for 2 seconds. Following this, the brief green flash of the
upper left and lower right LEDs will signal ready again. Throughout the day, as light levels change, the
camera exposure will be adjusted and the red LED will come on for a second followed by the green
flash to signal ready. Similarly, the flash capacitor needs to be "topped off" by a recharge operation
now and then. The lower left LED will glow red during this and the green flash will signal ready after
it completes.
Image Capture Sequence
When the camera detects motion and captures an image, both lower LEDs will flicker green for a short
period as the image data is written to the SD memory card. If capturing multiple images per trigger
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event, the time will increase accordingly. If the image was captured using the flash, the lower left LED
will turn red and the capacitor will be recharged. When all operations complete and the camera is
again ready, the upper left and lower right LEDs will briefly flash green. If the power switch is
depressed during the SD writing, the image in progress will be completed before the camera is shut
down.
Shut Down Sequence
After pressing the power button to turn off the camera, the LEDs will light up one-by-one in circular
sequence, first in green, then in red to indicate that power is turning off.
Storage, Configuration, and Features
SD Card
The internal memory card in the camera trap is a 2GB micro SD type. All images are stored on this
card. They are organized in folders that have a name corresponding to the date of capture of the images.
For example, all pictures captured on July 4th, 2011 will be in a folder named 070411. This card also
has a file named CAM4nnnn.log in the root folder that contains information about general operation
and any errors that may have been detected by the software. CAM4nnnn represents a camera ID which
has been assigned to each camera, and nnnn is a unique 4 digit number. This log file contains
important information for the developers and takes up very little memory; one year of camera operation
uses 0.03% of the SD card which is less than a typical image file. There’s no need to erase it.
SD Card Full
If the SD card fills to capacity during normal camera operation, the camera will automatically shut
down to conserve battery power. When the camera is turned on again, the left and right LEDs will
flicker on/off in an alternating red/green pattern. In order to return the camera to normal operation, files
need to be removed from the SD card.
SD Card Not Detected
If the SD card is not detected or cannot be initialized by the camera at power-on, the top-left and lowerright LEDs will flash red on/off repeatedly every couple of seconds. If the card is in there, turn the
camera off, make sure that it's properly seated in the card holder by taking it out and putting it back in
again, then power the camera on. If the card is not there, turn the camera off, insert the SD card, and
then turn the camera back on.
Camera Configuration
Due to the camera's minimalist design, there are no buttons or an LCD screen. Therefore, the camera's
configuration is set up using a computer file instead of buttons on the camera itself. The camera's
parameters are mirrored into a file named CamTrap.CTC, which is kept on the SD card's root folder
and also automatically copied to USB flash drives. Modifying the parameters in this file will cause the
parameters in the camera to update. The CamTrap.ctc file is modified using a computer application
called the Camera Trap File Manager.
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USB Operation
A USB Type A connector is located on the bottom of the camera next to the power switch. The camera
acts as a USB host for certain USB devices. The operations that can be performed using the camera's
USB port are as follows:
–
Use a USB flash drive to obtain copies of the .jpg files that are contained on the
camera's SD card.
–
Use a USB flash drive to update the camera trap configuration parameters
–
Use a USB flash drive to update the camera's firmware
–
Set the camera's clock and location using GPS satellite data by connecting a hand-held
GPS - receiver, or a GPS USB dongle.
In the future, the USB connector will also be able to be used to connect a smart phone or tablet
computer to the camera. This will enable the ability to view images, set the camera's parameters, and
update the camera's firmware from a smart phone or tablet device using a smart phone or tablet
software application.
Reading Image Files From The Camera
The images, a log file, and configuration file can all be accessed via the USB port so it is not necessary
to read data directly from the SD card. In the preferred mode of operation, called “incremental USB
backup”, all new images, the log file and the configuration file are automatically copied to the USB
drive when the camera is powered on with a USB storage device plugged into the port. The images that
are copied are tagged as archived on the SD card and will not be copied again as long as the USB
backup mode is incremental. This allows cameras to be periodically read out without having to transfer
all captured images every time. Using incremental backups ensures that the complete set of images is
preserved on the SD card in case something happens to the USB drive. At the end of a trial, when
cameras are returned from the field, the USB backup mode can be changed to “full + delete from SD
card” and the next USB transfer will copy all files from the SD card that are not already present on the
USB drive and delete all the files from the SD card. Thus, the SD card can be cleared without having to
open the card compartment. The reason for including a full copy with the delete is to provide a safety
mechanism so that images will not be erased mistakenly. If the same USB drive has been used all
along with a particular camera, it will already have copies of all of the images on that SD card and the
“full + delete” process will take very little time. If multiple USB drives were used or if images were
removed from the USB drive, copying the archived files for that camera onto the USB drive before
performing the “full + delete” operation will save time. Alternatively, the configuration option “Quick
SD Clean” can be used in conjunction with “incremental USB backup” to delete all image files on the
SD card that have been previously backup up to any USB drive. This mode should only be used if it is
known that all images files on the SD card have been safely archived to a PC.
Encrypting Images On The Camera
The camera can be configured to encrypt the image files that are stored on the camera's SD card. When
this feature is used, image data is encrypted using a password that is set in the camera's configuration.
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With encryption enabled, the camera encrypts the image data immediately upon capture and stores it in
a file that has the file extension .ENC. These files cannot be viewed until they are decrypted into .JPG
files using the Camera Trap File Manager's “Decrypt Image Files” tab. Thus, a poacher who steals a
camera will be unable to use the images stored on the camera to help locate animals. The stolen
camera will also be useless since the File Manager is needed to alter the configuration file to turn the
encryption setting off.
Encryption can be thought of as password protection of your images, and it works as follows. You
choose a password which gets stored on the computer on which you are running the File Manager
program, and transfer this same password to all of the cameras you are using. Images will only be able
to be decrypted using the computer that has the stored password. After the camera images are
decrypted, they become ordinary .JPG files that can be viewed on any computer.
Power Lock Button Feature
The camera configuration setting “Power Button Lock” is used to prevent the camera from being
inadvertently turned on during transit due to an object bumping against the push button. When the
camera has this setting enabled, it will automatically power itself down within seconds of when the
button is pressed. Once the camera is ready to be used, this setting must be cleared from the camera
configuration. To clear the “Power Button Lock”, insert a USB drive and turn it on. The camera will
quickly detect the presence of the USB device, clear the power button lock setting from the camera
configuration, and automatically shut down. It is now ready for normal operation.
Stealth LED Mode Feature
When this feature is enabled in the camera's configuration, the camera will only use LED indications
during the initial power-up sequence, and the first flash charge-up. After that, the LEDs will no longer
light up during camera operation.
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