User guide

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SenseCam v2.3 User Guide Page 18 of 31 10/03/2009

5. Tighten the lens using the set screw and allen key. Take care not to over-tighten; this

might result in permanent damage to the camera.

Steps 2, 5 and 6 above may also be used to fine-tune the focus of the SenseCam with the

lens as supplied. It is suggested that the unit be focussed using a visual target of high

contrast at a distance of between 1 and 2 metres from the camera for general-purpose use.

Special applications may require the camera to be focussed closer to or further from the

camera.

4.6. Internal flash memory

All the sensor and image data is stored on an SD card inside the SenseCam. The VGA

resolution images recorded by SenseCam are stored as compressed JPEG files with a typical

size of around 30k bytes. This allows for over 30 thousand images to be stored on the

standard 1GB SD card.

The SD card is not designed to be removed by the end user, and can only be accessed by

taking the back off the SenseCam and removing the PCB assembly. This operation is not

recommended, but would allow the card to be replaced if necessary. The SenseCam has only

been tested with 1GB and 2GB SD cards. The new 4GB SD cards will not work.

4.7. Battery lifetime and charging

The 980mAh lithium-ion battery in the SenseCam should give around 36 hours of

continuous operation, although this will depend on how frequently images are taken since

the VGA camera module and SD card are quite power-hungry. Very frequent image capture

may reduce battery life to around 12 hours. Turning the SenseCam „off‟ by pressing the

power button simply causes the SenseCam circuitry to enter a non-operational, very low

power sleep mode. In this mode the real-time clock, which is needed to time-stamp images

and sensor data when the camera is next switched on, is left running. The camera draws just

152uA in low power mode, so it will run for up to 9 months before the battery is completely

drained.

The battery charge can be „topped up‟ at any time by connecting the SenseCam to a power

source (either a USB host, USB hub or the supplied USB mains charger). It is strongly

recommended that you switch the SenseCam „on‟ before connecting it,

because this is the

only way to ensure that the red/green „charging‟ LED correctly reflects the state of the

device (see Section 4.3). The lithium-ion battery should be pretty immune to the „memory

effect‟ associated with other rechargeable battery chemistries, so „topping up‟ should not

affect the capacity of the battery.

If the battery charge becomes low during operation of the SenseCam, the green „power‟

LED will flash intermittently as a warning to the user (see Section 4.3). Eventually, the

charge will become so low that the SenseCam microcontroller will automatically switch the

device off. Trying to switch the unit back on in this condition will result in a low pitched

warble (see Section 4.4 above). Obviously in this case the SenseCam must be connected to a

power source with the unit still switched „off‟. After around 15 minutes of charging,

disconnect the SenseCam and switch it on (the battery should have enough charge to do

Even though the SenseCam will promptly switch itself off as soon as the connection is detected.