Rev 1.2
Light-to-Frequency EVM
User’s Guide
L
IGHT
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TO
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ONVERTER
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VALUATION
M
ODULE
O
VERVIEW
The Light-to-Frequency Converter Evaluation Module facilitates evaluation of the TAOS family of light-
to-frequency converter optical sensors through the use of a motherboard and a set of device-specific
daughterboards. The EVM is designed to interface via a USB port to a host PC running the Windows-
compatible host software application. Several of the daughterboards also feature light-emitting diode
(LED) light sources which can be controlled from the host software to allow evaluation of the sensors
in a variety of physical sensing arrangements.
G
ETTING
S
TARTED
On most PCs, installation will automatically start when the CD-ROM is inserted into the drive. If the
installation does not begin:
Click
Start
Click
Run
Type
D:\setup
and press
Enter.
IMPORTANT: Use the appropriate drive letter in the above
command to install the software. CD-ROMs are commonly
D:
The installation program will guide you through the product installation
Refer to the ReadMe file on CD for the latest installation instructions.
USB EVM H
ARDWARE AND
D
RIVER
D
ESCRIPTION
The specification and system requirements for the hardware portion of the Light-to-Frequency (LTF)
EVM USB module follow:
System Requirements:
Notebook or Desktop PC running Windows 98, 2000, NT4.0, XP
Host Connection:
USB v2.0 using A-type connector
EVM Connection:
Mini B-type connector
Software Installation:
CD-ROM
The Light-to-Frequency Converter EVM comes assembled and consists of three main parts:
1. A
motherboard
2.
Set of Six Daughterboards,
each with a different light-to-frequency converter sensor
3. A
USB cable
NOTE:
Please leave the LTF EVM installation CD-ROM inserted in the drive. This will simplify
the USB Driver Installation steps. The LTF EVM USB driver is located in the D:\FTDI directory
on the CD-ROM. This directory can be specified if it is necessary to manually install the driver
from a specific location.
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An Evaluation System for the TAOS Light-to-Frequency Converters
Using the enclosed USB cable, plug the mini-B connector into the EVM module. Using the other end
of the cable, plug the USB A-connector into a USB port on the computer. A Wizard should appear
instructing the user to load a USB driver. See the "Light-to-Frequency EVM Quick Installation" for
instructions on loading the USB driver.
See Appendix for schematic diagrams of the LTF EVM motherboard and daughterboards.
Figure 1 - EVM Motherboard
Motherboard
The Light-to-Frequency Converter EVM motherboard consists primarily of an integrated BASIC Stamp
BS2pe microcontroller, two Atmel ATTiny13 microcontrollers used as coprocessors, and a USB
interface. Two sockets, referred to as socket A (J4) and socket B (J7) (see Figure 1) accept any of the
six sensor daughterboards. There is a coprocessor associated with each daughterboard, and these are
labeled “A” and “B” on the motherboard. Frequency measurements, period measurements and PWM
control of the daugherboard LEDs are performed by either the BASIC Stamp or the coprocessors
under BASIC Stamp control. The EVM is shipped with an application programmed into the BASIC
Stamp which controls the communication between the BASIC Stamp, the sensor coprocessors, and the
host PC software application.
The EVM daughterboards are hot-pluggable, that is, they may be installed and removed while the EVM
and host application is running. The host application will recognize the installed daughterboard(s) and
invoke the appropriate daughterboard window(s).
Daughterboards
Six daughterboards are included with the Light-to-Frequency Converter EVM supporting the evaluation
of the following devices: TSL230RD, TSL235R, TSL237S, TSL237T, TSL245R, and TSL238D. Some of
the daughterboards contain LEDs in either transmissive or reflective configurations. The
daughterboard configurations are summarized below in Table 1.
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An Evaluation System for the TAOS Light-to-Frequency Converters
Table 1 - Daugherboard Configuration and Sensing Geometry
Device
TSL230RD
TSL235R
TSL237S
TSL237T
TSL245R
TSL238D
LED
N/A
Red
Red
Infrared
Infrared
Infrared
Configuration
N/A
Transmissive
Transmissive
Reflective
Reflective
Reflective
Geometry
Vertical
Horizontal
Horizontal
Vertical
Horizontal
Vertical
Any of the six daughterboards may be installed in either of the sockets A or B. To install a
daughterboard, align the connector on the bottom of the daughterboard with either of the sockets A
or B. Note that the connector is polarized and the daughterboard should be inserted such that the two
mounting holes in the corners opposite the side with the connector align over the threaded standoffs
on the motherboard. Press firmly over the connector to make sure that the daughterboard is seated
firmly in the socket. As explained earlier, the PC host application will recognize which daughterboards
are installed and invoke the appropriate windows inside the main application window. Optionally the
daughterboards may be held in place with 3/16” 4-40 machine screws inserted through the two
mounting holes into the threaded standoffs.
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An Evaluation System for the TAOS Light-to-Frequency Converters
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EVM A
PPLICATION
S
OFTWARE
Software Execution
To start the LTF EVM host application, click:
Start -> Programs -> TAOS Light-to-Frequency Converter EVM -> Light-to-Frequency
Converter EVM
After the EVM application is executed, a Main dialog window (see below) will appear.
Graphical User Interface (GUI)
The LTF EVM demo application consists of a main window with a control section on the left-hand side,
and up to two daughterboard windows depending upon how many daughterboards are installed.
Additionally a Strip Chart recorder window can be invoked which displays the data in a graphical
representation. Each window is explained in more detail in the following sections.
Figure 2 - Light-to-Frequency EVM Main Window
Control Window
The control window appears at the far left of the main application window. It provides control over
measurement mode and measurement update rate of both daughterboard windows. Each section is
explained in detail below.
Measurement Mode
The Measurement section allows selection of measurement mode of the sensor output frequency.
Available options are: Frequency, Period, and Long Period
Frequency measurement
uses the technique of counting pulses, or transitions (low-to-high) on the
sensor output pin. The counting takes place over a specified measurement time interval, or integration
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An Evaluation System for the TAOS Light-to-Frequency Converters
time. This integration time is controlled independently for each daughterboard. The frequency is then
determined by dividing the count value by the integration time to get units of Hz (cycles per second).
Since the number of counts obtained during the integration time interval determines the measurement
resolution, resolution can be improved by using longer integration times. The maximum count value
that can be obtained is 65535 (16-bit), so integration time must be chosen so that this maximum
count value is not exceeded.
Period measurement
uses the technique of measuring the time between pulses (i.e. low-to-high
transitions) on the sensor output pin. The EVM uses an internal hardware-based timer to measure this
time interval. The measurement resolution is 2µs with a maximum count value of 65535, therefore the
maximum time interval (period) that can be measured is 0.131s.
Long period measurement
uses a software loop to measure the time interval rather than a
hardware-based timer. After establishing an initial condition (such as a high-to-low or low-to-high
transition) this technique samples the output state from the sensor and increments a value used as a
counter. This process repeats until the state changes from the initial condition. The period is then
proportional to the number of counts obtained. Actual time is calculated by multiplying the count
value by the time it takes to execute a single pass through the loop. On the BS2pe used on the EVM,
this loop time is 0.00119s, or 1.19ms, and the maximum count value is 65535. Therefore the
maximum time interval (period) that can be measured is about 78s.
Each of the above three measurement techniques can give different resolution for a given frequency.
In general, for high frequencies it is best to use the Frequency measurement mode since this gives a
relatively high count value in a reasonable amount of time (integration time). For lower frequencies, a
longer integration time is required to get a high count value (high resolution). In this case Period
measurement mode can be used, which will result in a higher count value in a shorter amount of time,
since only the measurement of one period, or cycle, is required. For very low frequencies (less than
about 8Hz, or 1/0.131s), the maximum count of the Period measurement mode can be exceeded. In
this case the Long Period measurement mode can be used, allowing periods up to 78s (about 0.01Hz)
to be measured, although measurement times of this length are not practical in most cases.
Measurement mode can be selected independently for the daughterboards in sockets A and B.
Update Readings
The host software application periodically polls the EVM automatically and requests a measurement.
This polling, or update, interval can be adjusted in several steps between 0.1s and 10s using the Rate
slider. Note that this update rate is independent of the integration time used to measure frequency.
Therefore if the selected integration time exceeds the selected update rate, the update rate will be
decreased to allow the frequency measurement to be made. Additionally, if two daughterboards are
installed and measuring frequency, both integration times must be accommodated. Therefore the
actual update rate may be much slower than the rate selected. The actual update interval is shown
below the Rate slider. Automatic measurement update can be disabled and enabled using the Auto
Update check box.
Strip Chart Data Source
A strip chart may be invoked which provides a visual representation of the measurement data (for
more information on the Strip Chart see the section entitled Strip Chart). Option buttons select the
source of the data for the strip chart from either Socket A or Socket B.
Daughterboard Windows
Daughterboard windows provide control and display measurement results for each daughterboard
installed in the EVM motherboard. Although there are six different daughterboards, there are only two
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