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An Evaluation System for the TAOS Light-to-Frequency Converters
types of daughterboard windows – one for the TSL230RD daughterboard which does not utilize and
LED, and one for the other five daughterboards which utilize LEDs.
TSL230RD Daughterboard Window
The TSL230RD daughterboard window provides a graphical representation of the programmable
features of the TSL230RD device. The TSL230RD daughterboard window can be seen on the right in
Figure 2. Buttons are used to control the state of the sensitivity and output scaling input programming
lines on the evaluation device. The pattern of squares in the middle of the picture represents the
configuration of active photodiodes in the 100x, 10x, and 1x sensitivity modes. For more information
on the TSL230RD please refer to the TAOS TSL230RD Programmable Light-to-Frequency Converter
datasheet.
Integration Time
A slider provides adjustment of integration time between 0.01s and 3s for the frequency measurement
of the TSL230RD evaluation device. See the section "Measurement Mode" for more information on
frequency measurement.
Other Daughterboard Windows
The TSL235R, TSL237S, TSL237T, TSL245R, and TSL238D daughterboards share a common set of
features and therefore share a common window format. This daughterboard window format is shown
on the left in Figure 2. Controls are provided for LED brightness and sensor integration time, along
with several measurement options involving the use of the LED source.
LED Drive Duty Cycle
The EVM uses a pulse width modulation technique to control the brightness of the LED on the
daughterboard. Pulse width modulation varies the duty cycle, or percentage of time that the signal is
high, of the drive signal to the LED. This drive signal is then low-pass filtered to provide a continuous
DC signal. If the duty cycle is low, then the percentage of time that the LED is on is low (near 0%),
and the average power, and thus the brightness, is low. If the duty cycle is high (near 100%), then
the average power delivered to the LED is nearly maximum level. The duty cycle is controlled by an 8-
bit value (0-255) input using the LED Drive Duty Cycle slider.
Strobe
The Strobe option controls whether the LED is turned off after the frequency measurement is made. If
the Strobe check box is checked, then the LED will be turned on just before the measurement is
made, and turned off after making the measurement. When the LED is turned on, it will be set to the
brightness determined by the LED Drive Duty Cycle setting. Turning off the LED between
measurements will prevent the light from one daughterboard from affecting the measurements of an
adjacent daughterboard, and will minimize heating of the LED at high brightness levels.
Integration Time
A slider provides adjustment of integration time between 0.01s and 3s for the frequency measurement
of the TSL230RD evaluation device. See the section "Measurement Mode" for more information on
frequency measurement.
Measurement Options
There are two measurement options that may be activated when making measurements with the on-
board LED. The ambient subtraction option is activated when the Subtract Ambient check box is
checked. When this option is activated, each time the sensor is measured, and extra measurement is
made with the LED off. This value is stored and displayed as "Ambient". This value is then subtracted
from the actual frequency measurement and the subtracted value is displayed in the reading window.
The calculation used is as follows:
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