Rev. 0.2 10/12 Copyright © 2012 by Silicon Laboratories Si7005USB-DONGLE
Si7005USB-DONGLE
EVALUATION DONGLE KIT FOR THE Si7005
TEMPERATURE AND HUMIDITY SENSOR
1. Introduction
The Si7005 is a re lat ive hu m idit y an d t em p er at ur e envir on m en tal sens or in a 4 mm x 4 mm QFN package. Access
to the sens or ou tp u t is via a standar d I2C digital interface. The Si7005 is a highly-integrated devic e in co rp o ra ting a
humidity sensor, temperature sensor, signal conditioning, an analog-to-digital converter, control logic, and an I2C
interface.
2. Evaluation Kit Description
This document describes the operation of the Silicon Laboratories Si7005USB-DONGLE Rev 1.0 evaluation kit.
The Si7005 evaluation kit and accompanying graphical user interface software allow the user quick and easy
access to the features and functions of the Si7005 sensor as well as enabling the evaluation of the sensor’s
performance. The evaluation kit includes the following:
Si7005USB-DONGLE evaluation board consisting of one Si7005 sensor
Windows graphical user inter face softwar e for complete control of the Si7005 sensor (Windows XP, VISTA,
or 7 required)
Figure 1. Si7005USB-DONGLE
Figure 2. Si7005-EVB (Ordered Separately)
Si7005 C8051F381
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3. Software Setup
It is important that the software be installed before connecting the USB dongle to the PC; this ensures that the
software drivers are correctly installed.
To set up the software, run the file, setup.exe, from the supplied softwa re installation disk.
The Si7005 demo platform was developed based on National Instruments LabView™ platform. To install it, you
must accept the National Instruments end-user license agreeme nt shown in Figure 3.
Figure 3. National Instruments Software License Agreement
Continue through the following screens, which track the Graphical User Interface installation.
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Figure 4. Start Installation Screen
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Figure 5. Installer Update Screen
After this screen, you will see the installer for the Si7005 device drivers.
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Figure 6. Device Drivers Installer Screen
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4. Hardware Setup and Software Operation
Once the GUI installation is complete, connect the Si7005 USB dongle to your PC. Your PC should automatically
recognize the USB dongle and use the newly-installed driver.
Next, find the icon for the Si7005 GUI, which should be easily found under recently-installed programs from the
start menu, under ProgramsSilicon LaboratoriesSi700x Evaluation Software or at C:\program files\Silicon
Laboratories\Si700x\.
With all the hardware plugged in and once your PC identifies the USB dongle, launch the GUI.
The GUI itself is simple to use. Figure 7 shows a screen shot of the GUI.
Figure 7. GUI Screen
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The USB dongle contains one Si7005 relative humidity and temperature sensor and can also support one
additional Si7005 sensor at conne ctor J2 by connecting a Si7005-EVB (ordered separately).
To start the evaluation, click the “INIT” button, the GUI will recognize how many sensors are connected.
Select temperature units by clicking on the “Select Te mperature Units” button, the button label will toggle between
“Deg C” and “Deg F” indicating the selection of either degrees Celsius or degrees Fahrenheit.
In the “Enter Sample Interval (seconds)” number box, the time interval between samples can be entered, a value
between 1 and 65535 seconds can be entered.
The Si7005 on-chip heater can be enabled/disabled using the “On-chip Heater” toggle button. The heaters of all
the connected sensors are controlled simultaneously.
The upper chart by default displays temperature; this can be changed to dew point b y clicking o n the selection box
located directly under the Silicon Labs logo. When logging data to file, the upper chart should be set to display
temperature since dew point is already automatically logged to file.
The default Y-axis range on each chart is from 0 to 100. To change this range, simply click on the upper or lower
value on the chart axis and type in an alternative value. The axis can also be configured to auto-range to the
displayed da ta by right-clicking on the chart a nd select ing “Autoscale Y”. The same configuration changes can be
made to the X-axis.
If a log of the data is desired, click “Create Log File?” button to “Yes”.
Click “START” to begin collecting data. If “Create Log File?” is enabled, a dialog box will appear requesting a file
name and save location. Note that the “Create Log File?” button must be set to “YES” before clicking on the “Start”
button in order to log dat a . The time base of the log file ca n be chosen to be absolute da te and tim e or relative time
in seconds.
To stop data collection, click “STOP”. To exit the GUI click “QUIT”.
The GUI automatically adjusts for the temperature and non-linearity effect of the RH-sensitive film of the Si7005
The data logged to file is saved in a tab delimited text file format, which can be easily opened in a spreadsheet
application such as Microsoft Excel, as shown in Figure 8.
Figure 8. Logged Data Displayed in Excel with Absolute Date and Time time Base
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Figure 9. Logged Data Displayed in Excel with Relative Time Base in Seconds
4.1. Calculation of Dew Point Value
The Si7005 measures both temperature (T) and relative humidity (RH). These two values can be used to
approximate the dew point (Td).
The calculation used is based on the August-Roche-Magnus approximation for the saturation vapour pressure of
water in air as a function of temperature, it is considered valid for:
0 °C < T < 60 °C
1% < RH < 100%
0°C < T
d < 50 °C
TdbT,RH
aT,RH–
-------------------------------
Where
T,RH
aT
bT+
-------------RH
100
----------
ln+=
=
a 17.625
b243.04
=
=
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5. Si7005 USB Dongle Description
The USB Dongle facilitates communication between the Si7005 and the PC. This function is enabled by the Silicon
Laboratories' C8051F381 microcontroller. The pin connections for connector J2 are shown in Figure 10. A full
circuit diagram of the bo ard is shown in Figure 11.
Figure 10. Ribbon Cable Pin Assignments
5.1. Si7005 USB Dongle Schematic
The Si7005USB-DONGLE is a simple board containing an Si7005 relative humidity and temperature sensor, a
C8051F381 USB microcontroller, a USB ty pe A connector, and an auxiliary connector for co nnection to a second
Si7005 sensor. Discrete component re qu ire m en ts are minim al, demo nst ra tin g th e ea se -o f- use of the Si70 05 .
VDD
CS
GND
SDA
PROG
SCL
1
2
3
4
5
61
2
3
4
5
6
Ribbon
Connector
USB Dongle
Ribbon
Connector
Si7005 EVB
Si7005USB-DONGLE
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GND C2CK C2D
RESETn
SCL2
SDA2
CS2
+3V3
C1
4.7uF
C4
0.1uF
R8 0
TP5
VDD
P1
USB TYPE A
+V 1
D- 2
D+ 3
GND 4
SH
5SH
6
R3
2K
R4
2K
U1
Si7005
DNC 13
DNC 14
SDA
4
DNC
6
SCL
3
DNC
5
DNC
2
GND
1
CS 15
DNC 16
DNC 17
DNC 18
DNC
12
GND
11
Cext
10
GND
8
VDD
9
GND 19
DNC 24
DNC 20
DNC 23
DNC 22
DNC 21
DNC
7EPAD 25
R6
332
R7 0
J2
FH12
1
12
23
34
45
56
6
R111K
TP2
GND
C3
4.7uF
C5
0.1uF
D1
SP0503BAHT
R10
10K
R5 0
R9 0
D2
AMBER
C2
0.1uF
U2
C8051F381
VDD 6
REGIN 7
GND
3
VBUS 8
D+
4D-
5
P0.0 2
P0.1 1
P0.2 32
P0.3 31
P0.4 30
P0.5 29
P0.6 28
P0.7 27
P1.0 26
P1.1 25
P1.2 24
P1.3 23
P1.4 22
P1.5 21
P1.6 20
P1.7 19
P2.0 18
P2.1 17
P2.2 16
P2.3 15
P2.4 14
P2.5 13
P2.6 12
P2.7 11
RST/C2CK
9
P3.0/C2D
10
TP3
SCL
J1
C6
4.7uF
TP4
SDA
R1
10K
C7
0.1uF
R2
10K
TP1
CS
Figure 11. USB Dongle Circuit Schematic
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5.2. Si7005 USB Dongle Board Layers
Figure 12. Si7005 Dongle Board Layout Top Layer
Figure 13. Si7005 Dongle Board Layout Bottom Layer
Note from Figures 1, 12, and 13, that there is no ground plane around the Si7005 and that there is a cutout in the
PCB between the Si7005 and other circuitry. While these are not requirements for successful operation of the
Si7005, they do (in the case of the dongle board) provide thermal isolation from heat sources, such as the host PC
and MCU circuitry. The intention of this evaluation board layout is to demonstrate the concept of thermal isolation
between the Si7005 and the system board. In many applications, the system designer will use the Si7005 to sense
the temperature of the air around it and not that of the system PCB.
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6. Si7005-EVB Description
6.1. Si7005 EVB Schematic
The evaluation board is a simple board containing just the Si7005 sensor, two capacitors and a ribbon connector
for connection to the USB dongle board. The circuit diagram and layout are shown in Figures 14, 15 and 16.
8
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'1&
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6&/
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'1&
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-
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Figure 14. Si7005 Evaluation Board Schematic
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6.2. Si7005 Evaluation Board Layers
Figure 15. Si7005 Evaluation Board Layout Top Layer
Figure 16. Si7005 Evaluation Board Layout Bottom Layer
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7. Additional Reference Resources
Si7005 data sheet
AN607: Si70xx Humidity Sensor Designer's Guide
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DOCUMENT CHANGE LIST
Revision 0.1 to Revision 0.2
Si7005USB-DONGLE
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