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Introduction
The CCD (Charge Coupled Device) Array Interface is a general
purpose board which continually scans a one dimensional 128
element light sensitive array and produces a stream of digital output
codes corresponding to the measured light intensity at each pixel
element. The 8-bit output values represent the relative energy
absorbed at each pixel during the interval in which the last set of
data was sent. While these seems quite intuitive, the TC102-1
CCD array chip provides only a raw sensor array; built-in features
implemented in the hardware on the CCD Array Reader Board deliver
the easy-to-use digital data stream.
Automatic High-Speed Scanning
All timing operations are
generated on the board, which simplifies its usage, and allows the
array to be scanned at relatively high speed. The various
clock signals required by the TC102-1, A/D converter, analog
circuitry and the computer interface's handshake lines are all
created by digital circuitry on the CCD Array Reader Board. This
relievs the computer from the task of controlling the CCD Array and
associated circuitry so that it may acquire data more rapidly.
The CCD Array Reader Board includes
built in power supply circuits to generate a number of voltage levels
required by the various components; the user only need provide a
plus and minus sixteen volt power supply. Finally, a ten pin
connector and cable are provided so that the data may be read in by
a computer. Two special handshake signals are provided on this
interface connector which make to task of acquiring the data
relatively simple. Though the CCD Array Interface board is quite
complex, these features make its usage quite simple.
Automatic Offset Adjustment
The board features automatic self
calibrating offset adjustment, to compensate for the varying voltage
offset levels produced by the CCD Array component. This offset
correction technique results in pixels which receive virtually no light
producing a digital code of zero without requiring the adjustment of
calibration trim pots for different lighting conditions, scanning
speeds, ambient temperatures, or other varying conditions which
may change the actual voltage output levels produced by the CCD
Array component.
Automatic Gain Control
The board also features automatic sensitivity
control, which results in output codes of 255 (the maximum) for
pixels which are saturated (the maximum light intensity). The
combination of Automatic Offset Adjustment and Automatic Gain Control
assure that the output stream will represent the relative range of
intensities received by the CCD array using the full dynamic range
of the 8-bit data.
Full Saturation Detection
A light
emitting diode is provided on the board to indicate a fully saturated
condition in which the array has been exposed to so much light that
it is no longer functioning properly. If the TC102-1 is exposed to
too much total incident energy during a sampling period, its detectors
do not operate properly. This condition is detected by the CCD Array
Reader Board's circuitry.
Applications
The CCD Array Reader Board is intended to be a general purpose
device for use in applications where one dimentional imaging
of relative light intensity is required. It was the intention
of the OSU Physics Department to use a linear image detector of
this nature to acquire position data with time of objects on an
air track in ungraduate physics courses. Students would conduct
their classical physics lab experiments (with small lights mounted
to the objects) and obtain much more
data from this board than they would have collected otherwise.
The CCD Array Reader Board was demonstrated using a video camera
lens and a small light bulb mounted to a battery. Though it
performed very well sampling at relatively high speed, I doubt
it has seen any use in undergrad physics labs. In all likelyhood,
the board is sitting in the back of some physics storeroom on the OSU
campus. Oh well.
Of course, I passed the course with an 'A' and everyone was suprised and
impressed that it worked so well. Several others had tried to get
these damn TC102-1 chips to work with fairly unimpressive results.
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