TCS230 Datasheet, PDF (6/8 Pages) List of Unclassifed Manufacturers – PROGRAMMABLE COLOR LIGHTTOFREQUENCY CONVERTER

TCS230
PROGRAMMABLE
COLOR LIGHTĆTOĆFREQUENCY CONVERTER
TAOS046 – JANUARY 2003
APPLICATION INFORMATION
Power supply considerations
Power-supply lines must be decoupled by a 0.01-µF to 0.1-µF capacitor with short leads mounted close to the
device package.
Input interface
A low-impedance electrical connection between the device OE pin and the device GND pin is required for
improved noise immunity.
Output interface
The output of the device is designed to drive a standard TTL or CMOS logic input over short distances. If lines
greater than 12 inches are used on the output, a buffer or line driver is recommended.
Photodiode type (color) selection
The type of photodiode (blue, green, red, or clear) used by the device is controlled by two logic inputs, S2 and
S3 (see Table 1).
Output frequency scaling
Output-frequency scaling is controlled by two logic inputs, S0 and S1. The internal light-to-frequency converter
generates a fixed-pulsewidth pulse train. Scaling is accomplished by internally connecting the pulse-train output
of the converter to a series of frequency dividers. Divided outputs are 50%-duty cycle square waves with relative
frequency values of 100%, 20%, and 2%. Because division of the output frequency is accomplished by counting
pulses of the principal internal frequency, the final-output period represents an average of the multiple periods
of the principle frequency.
The output-scaling counter registers are cleared upon the next pulse of the principal frequency after any
transition of the S0, S1, S2, S3, and OE lines. The output goes high upon the next subsequent pulse of the
principal frequency, beginning a new valid period. This minimizes the time delay between a change on the input
lines and the resulting new output period. The response time to an input programming change or to an irradiance
step change is one period of new frequency plus 1 µS. The scaled output changes both the full–scale frequency
and the dark frequency by the selected scale factor.
The frequency-scaling function allows the output range to be optimized for a variety of measurement
techniques. The scaled-down outputs may be used where only a slower frequency counter is available, such
as low-cost microcontroller, or where period measurement techniques are used.
Measuring the frequency
The choice of interface and measurement technique depends on the desired resolution and data acquisition
rate. For maximum data-acquisition rate, period-measurement techniques are used.
Output data can be collected at a rate of twice the output frequency or one data point every microsecond for
full-scale output. Period measurement requires the use of a fast reference clock with available resolution directly
related to reference clock rate. Output scaling can be used to increase the resolution for a given clock rate or
to maximize resolution as the light input changes. Period measurement is used to measure rapidly varying light
levels or to make a very fast measurement of a constant light source.
Maximum resolution and accuracy may be obtained using frequency-measurement, pulse-accumulation, or
integration techniques. Frequency measurements provide the added benefit of averaging out random- or
high-frequency variations (jitter) resulting from noise in the light signal. Resolution is limited mainly by available
counter registers and allowable measurement time. Frequency measurement is well suited for slowly varying
or constant light levels and for reading average light levels over short periods of time. Integration (the
accumulation of pulses over a very long period of time) can be used to measure exposure, the amount of light
present in an area over a given time period.
Copyright E 2003, TAOS Inc.
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The LUMENOLOGYr Company
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