An Evaluation System for the TAOS Light-to-Frequency Converters
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Reading = ( Ambient) - Ambient
Ambient subtraction is useful in cases where measurements are being made using the LED in the
presence of significant ambient light. Ambient subtraction only works well in situations in which the
ambient light is steady or varying slowly. Flickering or rapidly varying ambient light will not be
properly subtracted since the measured value may change between the time that the ambient and
signal are measured.
Ratiometric measurements represent the measured value as a ratio between the most recent
measurement and a previous reference measurement. Making a ratiometric measurement is a two-
step process. First a reference value must be recorded. This is accomplished by setting up the desired
reference condition, then clicking the Reference button. This reference value is then stored and
displayed as “Reference”. This value is used as the standard for subsequent measurements. The
ratiometric measurement is calculated as follows:
Reading = Signal / Reference
Note that both measurement options can be used together. In this case, the following calculation is
used:
Reading = (Ambient – Ambient) / (Ref Ambient – Ambient)
Strip Chart
The Strip Chart window is invoked by selecting menu option View, Strip Chart. The Strip Chart is a
graphical representation of the EVM readings as time progressing from left to right. Each time a new
reading is taken, the plot moves to the right and the new reading is added at the left. The Strip Chart
is useful for visualizing slowly changing lighting conditions. The vertical scale may be set automatically
or manually. The vertical scale is set automatically when the Auto check box is checked. When Auto is
not checked, the vertical scale may be set using the Vertical Scale drop-down list. Note that if the
vertical scale is set too low the plot may not appear (it will be off the top of the chart).
Closing the Application
To close the host application select menu option File, Exit, press Ctrl + Q, or click the close button in
the main window control box.