Evaluation Board User Guide
UG-079
One Technology Way • P. O . Box 9106 • Norwood, MA 02062-9106, U.S.A. • Tel : 781.329.4700 • Fax : 781.461.3113 • www.analog.com
Evaluation Board for the AD7781 20-Bit, Pin-Programmable,
Low Power, Sigma-Delta ADC
FEATURES
Full-featured evaluation board for the AD7781
Standalone USB interface
Various linking options
PC software for control of AD7781
GENERAL DESCRIPTION
This user guide describes the evaluation board for the AD7781,
which is a pin programmable, low power, 20-bit sigma-delta
(Σ-Δ) ADC. The AD7781 is a complete analog front end for
low frequency measurement applications such as bridge sensor
systems. It contains one differential input and includes a low
noise instrumentation amplifier. The output data rate can be
programmed to 10 Hz or 16.7 Hz. The AD7781 also has an
on-board clock, eliminating the need for an external clock. It
employs a Σ-Δ conversion technique to realize up to 20 bits
of no missing codes performance. The input signal is applied
to an analog modulator. The modulator output is processed by
an on-chip digital filter. The analog input channel of the
AD7781 accepts analog input signals of ±V
REF
or ±V
REF
/128.
With the update rate programmed to 10 Hz, the rms noise
is 44 nV when the gain is 128. Simultaneous 50 Hz/60 Hz
rejection is available at both output data rates.
Full data on the AD7781 is available in the AD7781 data sheet
available from Analog Devices, Inc., and should be consulted in
conjunction with this user guide when using the evaluation board.
The evaluation board interfaces to the USB port of an IBMcompatible PC. Software is available with the evaluation board
that allows users to easily communicate with the AD7781.
Note that the AD7781 evaluation board software should be
installed before connecting the AD7781 evaluation board
to the PC.
Another component on the AD7781 evaluation board is the
ADP3303 high precision, low power, 3.3 V output voltage
regulator, which is used to power the USB/SPI interface.
PLEASE SEE THE LAST PAGE FOR AN IMPORTANT
WARNING AND LEGAL TERMS AND CONDITIONS.
FUNCTIONAL BLOCK DIAGRAM
AVDD
LOADCELL
CONNECTOR
ANALOG
INPUTS
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AD7781
VOLTAGE
REGULATOR
SPI/USB
INTERFACE
Figure 1.
USB
CONNECTOR
PC AND
LabVIEW™
BASED
SOFTWARE
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TABLE OF CONTENTS
Features .............................................................................................. 1
General Description ......................................................................... 1
Functional Block Diagram .............................................................. 1
Revision History ............................................................................... 2
Evaluation Board Hardware ............................................................ 3
Power Supplies .............................................................................. 3
Links ............................................................................................... 3
Setup Conditions .......................................................................... 4
Sockets ........................................................................................... 4
Interfacing to the Evaluation Board ........................................... 5
REVISION HISTORY
2/10—Revision 0: Initial Version
Evaluation Board Software ...............................................................6
Software Description ....................................................................6
Installing the Software ..................................................................6
Using the Software ........................................................................6
Main Window ................................................................................7
Weighscale Demo Window ..........................................................8
Evaluation Board Schematic and Artwork .....................................9
Ordering Information .................................................................... 13
Bill of Materials ........................................................................... 13
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EVALUATION BOARD HARDWARE
POWER SUPPLIES
The AD7781 evaluation board is powered via the 5 V supply
from the USB connector, J1. This 5 V supply can be used to
power the AD7781 directly. A 3.3 V regulated voltage from the
on-board ADP3303 (a high precision, low power, 3.3 V output
voltage regulator) can also be used. Alternatively, the AD7781 can
be powered using an external 3 V or 5 V power supply via J2.
Table 1. Evaluation Board Link Settings
Link Default Description
LK1, LK2 In
LK3, LK4 In
LK5 3.3 V LK5 is used to select the power source for AVDD on the AD7781.
LK6 to LK11 In
LK12, LK13, LK14 In
LK15 10 Hz
LK16 128
These links are used to connect the AIN(+) and AIN(−) inputs to AV
analysis can be performed. With these links removed, an external voltage may be applied to AIN(+)/AIN(−)
using the SMB connectors.
With LK3 and LK4 in place, AV
REFIN(−) is connected to GND. To use another reference source, remove LK3 and LK4.
In Position A, LK5 selects an external power supply, supplied via J2.
In Position B, LK5 selects the 3.3 V regulated output from the on-board ADP3303 voltage regulator.
In Position C, LK5 selects the 5 V supply from the USB connector, J1.
These links connect the serial interface pins of the AD7781 to the SPI interface of the microcontroller. The
links should be in place to use the AD7781 evaluation board software. With these links removed, the AD7781
can be interfaced to an external microcontroller.
These links are used for the bridge power-down switch. With LK12 inserted, the bridge power-down switch is
connected to AV
should be open when LK12 is inserted.
LK13 and LK14 are used when a load cell is connected to Header J4. LK12 should be left open. With LK13
inserted, the bridge power-down switch is connected to Header J4. The low side of the load cell can be
connected to GND through the bridge power-down switch. With LK14 inserted, the low side of the load cell is
connected directly to GND. The terminal REFIN(−) should be shorted to the GND/PSW terminal on Header J4
to enable the previous functions.
LK15 is used to select the output data rate for the AD7781. With LK15 in Position 10 Hz, the output data rate is
set to 10 Hz. When LK15 is in Position 16.7 Hz, the output data rate is set to 16.7 Hz.
LK16 is used to select the gain of the AD7781. With LK16 in Position 1, the gain is set to 1. With LK16 in
Position 128, the gain of the AD7781 is set to 128.
through an LED. When the bridge power-down switch is closed, the LED turns on. LK13
DD
is used as the reference to the AD7781. REFIN(+) is connected to AVDD and
DD
LINKS
There are sixteen groups of link options that must be set for the
required operating setup before using the evaluation board. The
functions of these link options are outlined in Tab le 1.
/2. With this configuration, a noise
DD
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SETUP CONDITIONS
Take care before applying power and signals to the evaluation
board to ensure that all link positions are set per the required
operating mode. Tabl e 2 shows the position in which all the
links are initially set.
Table 2. Initial Links and Positions
Link No. Position Function
LK1, LK2 In AIN(+) and AIN(−) are shorted to AVDD/2.
LK3, LK4 In The reference voltage is set to 3.3 V (AVDD).
LK5 B The 3.3 V supply is used as AVDD for the AD7781.
LK6 to LK11 In The AD7781 is interfaced to the on-board microcontroller.
LK12 In The bridge power-down switch is connected to AVDD.
LK13 Out The bridge power-down switch is disconnected from Header J4.
LK14 In Terminal GND/PSW of Header J4 is connected to GND.
Table 3. Socket Functions
Socket Description
AIN+ Subminiature BNC (SMB) connector. The analog input signal for the AIN(+) input of the AD7781 is applied to this socket.
AIN− Subminiature BNC (SMB) connector. The analog input signal for the AIN(−) input of the AD7781 is applied to this socket.
REFIN+
REFIN−
J4 6-pin terminal block. This is used to connect an external load cell to the AD7781 evaluation board.
Subminiature BNC (SMB) connector. This socket is used in conjunction with REFIN− to apply an external reference to the AD7781.
The voltage for the REFIN(+) input of the AD7781 is applied to this socket.
Subminiature BNC (SMB) connector. This socket is used in conjunction with REFIN+ to apply an external reference to the AD7781.
The voltage for the REFIN(−) input of the AD7781 is applied to this socket.
SOCKETS
There are five sockets relevant to the operation of the AD7781
on this evaluation board. The functions of these sockets are
outlined in Tab l e 3.
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INTERFACING TO THE EVALUATION BOARD
Interface to the evaluation board is via a standard USB
connector, J1. J1 is used to connect the evaluation board
to the USB port of a PC. A standard USB connector cable
is included with the AD7781 evaluation board to allow the
evaluation board to interface with the USB port of the PC.
Because the board is powered via the USB connector, there
is no need for an external power supply, although if preferred,
one may be connected via J2.
Communication between the AD7781 and the PC is via the
USB/SPI interface. The on-board USB controller (U2) handles
this communication.
To set up the USB/SPI interface, use the following procedure:
1. Install the AD7781 evaluation board software using the
supplied AD7781 evaluation board CD before connecting
the board to the PC.
2. After the AD7781 evaluation board software is installed,
connect the board to the PC via J1 on the AD7781 evaluation
board and via the USB port on the PC using the supplied
USB connector cable. The PC automatically finds the new
USB device and identifies it as the AD779x Evaluation Board.
3. Follow the on-screen instructions that appear. During the
installation process if the Hardware Installation Wizard
appears as shown in Figure 2, click Continue Anyway
to successfully complete the installation of the AD7781
evaluation board.
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Figure 2. Hardware Installation Window
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EVALUATION BOARD SOFTWARE
SOFTWARE DESCRIPTION
The AD7781 evaluation board is shipped with a CD containing
software that can be installed onto a standard PC to control the
AD7781. The software communicates with the AD7781 through
the USB cable, which accompanies the board. The software allows
you to read conversion data from the AD7781. Data can be read
from the AD7781 and displayed or stored for later analysis. For
further information, see the AD7781 data sheet available from
Analog Devices.
INSTALLING THE SOFTWARE
Use the following steps to install the software:
1. Start Windows® and insert the CD.
2. The installation software should launch automatically. If it
does not, use Windows Explorer to locate the setup.exe file
on the CD. Double-click this file to start the installation
procedure.
3. At the prompt, select a destination directory, which is
C:\Program Files\Analog Devices\AD7781 by default.
Once the directory is selected, the installation procedure
copies the files into the relevant directories on the hard
drive. The installation program creates a program group
called Analog Devices with the subgroup AD7781 in the
Start menu of the taskbar.
4. Once the installation procedure is complete, double-click
on the AD7781 icon to start the program.
USING THE SOFTWARE
Figure 3 shows the main window that is displayed when the
program starts. The Main Window section briefly describes
the various menu and button options in the main window.
The data that has been read can be exported to other packages,
such as MathCAD™ or Microsoft® Excel, for further analysis.
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Figure 3. AD7781 Evaluation Software Main Window
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MAIN WINDOW
Menu Bar
File
The File menu allows you to read previously stored data for
display or analysis, write the current set of data to a file for
later use, and exit the program.
About
The About menu provides information on the revision of
software used.
Buttons
Reset
This button allows you to reset the AD7781 software.
Exit
This button allows you to exit the software. It serves the same
purpose as Quit in the File pull-down menu.
Sample
This button allows you to read a number of samples from
the AD7781. Noise analysis is then performed on the samples.
These samples can be stored for further analysis. The sample
size is entered in the Num Samples text box.
Continuous
This button allows you to read a number of samples continuously.
The software gathers a number of samples as specified by the
Num Samples text box, performs noise analysis on the samples,
and gathers the next group of samples.
Weig hs c ale D emo
This button allows you to access the weighscale demonstration
software.
Output Data Rate
This text box displays the output data rate of the AD7781.
Gain
This text box displays the gain of the AD7781.
Status Bits
This text box displays the status bits of the AD7781.
Wa ve f o r m
The gathered conversions are displayed in graph form.
Histogram
The gathered samples are used to generate a histogram.
Codes
The gathered samples can be displayed in codes or in voltage
format. When the Codes button is selected, the values are
displayed as code. The Codes button changes to Vo l t s . To
display the information in volts, click Vo lt s .
Reference
Enter the value of the external reference in the Reference (V)
text box.
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UG-079 Evaluation Board User Guide
WEIGHSCALE DEMO WINDOW
Click Wei ghs ca le D emo (in the main window) to access
the weighscale demo window (see Figure 4). The AD7781
evaluation board has a header, J3/J4, which allows you to
interface the ADC to a load cell. To connect a load cell to the
AD7781 evaluation board, LK1, LK2, LK3 and LK4 must be
removed. A 6-wire load cell can be connected to J3/J4. With
the load cell connected to the evaluation board, click the
RUN button (the button changes to a STOP button after
being clicked). The software then begins reading conversions
from the AD7781. The output data rate and gain are continuously monitored so you can change either the gain or output
data rate within the weighscale demo window. The output data
rate and gain being used by the AD7781 are reflected in the
Output Data Rate and Gain windows. The maximum weight
being applied to the load cell must be entered in the Full-Scale
Weig ht (Kg ) window. The Zero-Scale Calibration button
performs an offset calibration, which is useful to remove the
load cell TARE. With the full-scale weight placed on the load
cell, a full-scale calibration is performed by clicking the Full-
Scale Calibration button.
To stop conversions, click the STOP button. To exit the
Weig hs c ale De mo, click the BACK button.
Figure 4. AD7781 Evaluation Software Weighscale Demo Window
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EVALUATION BOARD SCHEMATIC AND ARTWORK
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Figure 5. AD7781 Evaluation Board Schematic
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Figure 6. AD7781 Evaluation Board—Solder Side View
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Figure 7. AD7781 Evaluation Board—Component Side View
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Figure 8. AD7781 Evaluation Board—Component Layout Diagram
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ORDERING INFORMATION
BILL OF MATERIALS
Table 4.
Qty Reference Designator Description Manufacturer, Part No.
Integrated Circuits
3 U1, U5, U6 24-bit Σ-Δ ADC Analog Devices, AD7781BRZ
1 U2 USB controller Cypress Semiconductor Corporation, CY7C68013A-56LFXC
1 U3 EEPROM Microchip Technology, Inc., 24LC64-I/SN
1 U4 3.3 V Regulator Analog Devices, ADP3303ARZ-3.3
1 Y1 24 MHz crystal AEL Crystals, X24M000000S244
2 D1, D2 Green LED Kingbright, Elec. Co., Ltd, KP-2012SGC
1 L1 Ferrite bead Meggitt Sigma, BMB2A0300AN1
1 D3 Diode Micro Commercial Components Corp., DL4001-TP
Capacitors
4 C1 to C4 Capacitors Not inserted
2 C5, C6 100 pF ceramic AVX Corporation, 06035A101JAT2A
15
3 C7, C10, C14, C21, C24 10 μF tantalum AVX Corporation, TAJA106M016R
2 C12, C13 1 μF ceramic Yageo Corporation, 2238 246 19863
1 C17 2.2 μF tantalum EPCOS AG, B45196E2225K109
2 C19, C20 12 pF ceramic Phycomp, 2238 867 15129
Resistors
7 R1 to R4, R9, R18 0 Ω resistor Phycomp, 232270296001
2 R5, R6 5 kΩ resistor Tyco Electronics, RN73C2A4K99BTG
4 R10 to R15 1 MΩ resistor Multicomp, MC 0.063W 0603 1% 1M
2 R16, R17 100 kΩ resistor Multicomp, MC 0.063W 0603 1% 100K
4 R19 10 kΩ resistor Multicomp, MC 0.063W 0603 1% 10K
1 R7, R20 1 kΩ resistor Multicomp, MC 0.063W 0603 1% 1K
2 R21, R22 2.2 kΩ resistor Multicomp, MC 0.063W 0603 1% 2K2
Links
13 LK1 to LK4, LK6 to LK14, (2 × 1 way) Pin headers Harwin Plc, M20-9990246
2 LK15, LK16 (3 × 1 way) Pin headers Harwin Plc, M20-9990246
1 LK5 (3 × 2 way) Pin headers Harwin Plc, M20-9980346
16 At LK1 to LK16 Shorting plugs Harwin Plc, M7566-05
Connectors
4 AIN+, AIN−, REFIN+, REFIN− SMB connector Not inserted
1 J1 USB Mini-B connector Molex, 565790576
2 J3, J4 3-way terminal block Phoenix, 1725672
1 J2 2-way terminal block Camden Electronics Ltd., CTB5000/2
C8, C9, C11, C15, C16, C18, C22, C23, C25
to C31
0.1 μF ± 10% ceramic AVX Corporation, CM105X7R104K16AT
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NOTES
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NOTES
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NOTES
ESD Caution
ESD (electrostatic discharge) sensitive device. Charged devices and circuit boards can discharge without detection. Although this product features patented or proprietary protection
circuitry, damage may occur on devices subjected to high energy ESD. Therefore, proper ESD precautions should be taken to avoid performance degradation or loss of functionality.
Legal Terms and Conditions
By using the evaluation board discussed herein (together with any tools, components documentation or support materials, the “Evaluation Board”), you are agreeing to be bound by the terms and conditions
set forth below (“Agreement”) unless you have purchased the Evaluation Board, in which case the Analog Devices Standard Terms and Conditions of Sale shall govern. Do not use the Evaluation Board until you
have read and agreed to the Agreement. Your use of the Evaluation Board shall signify your acceptance of the Agreement. This Agreement is made by and between you (“Customer”) and Analog Devices, Inc.
(“ADI”), with its principal place of business at One Technology Way, Norwood, MA 02062, USA. Subject to the terms and conditions of the Agreement, ADI hereby grants to Customer a free, limited, personal,
temporary, non-exclusive, non-sublicensable, non-transferable license to use the Evaluation Board FOR EVALUATION PURPOSES ONLY. Customer understands and agrees that the Evaluation Board is provided
for the sole and exclusive purpose referenced above, and agrees not to use the Evaluation Board for any other purpose. Furthermore, the license granted is expressly made subject to the following additional
limitations: Customer shall not (i) rent, lease, display, sell, transfer, assign, sublicense, or distribute the Evaluation Board; and (ii) permit any Third Party to access the Evaluation Board. As used herein, the term
“Third Party” includes any entity other than ADI, Customer, their employees, affiliates and in-house consultants. The Evaluation Board is NOT sold to Customer; all rights not expressly granted herein, including
ownership of the Evaluation Board, are reserved by ADI. CONFIDENTIALITY. This Agreement and the Evaluation Board shall all be considered the confidential and proprietary information of ADI. Customer may
not disclose or transfer any portion of the Evaluation Board to any other party for any reason. Upon discontinuation of use of the Evaluation Board or termination of this Agreement, Customer agrees to
promptly return the Evaluation Board to ADI. ADDITIONAL RESTRICTIONS. Customer may not disassemble, decompile or reverse engineer chips on the Evaluation Board. Customer shall inform ADI of any
occurred damages or any modifications or alterations it makes to the Evaluation Board, including but not limited to soldering or any other activity that affects the material content of the Evaluation Board.
Modifications to the Evaluation Board must comply with applicable law, including but not limited to the RoHS Directive. TERMINATION. ADI may terminate this Agreement at any time upon giving written notice
to Customer. Customer agrees to return to ADI the Evaluation Board at that time. LIMITATION OF LIABILITY. THE EVALUATION BOARD PROVIDED HEREUNDER IS PROVIDED “AS IS” AND ADI MAKES NO
WARRANTIES OR REPRESENTATIONS OF ANY KIND WITH RESPECT TO IT. ADI SPECIFICALLY DISCLAIMS ANY REPRESENTATIONS, ENDORSEMENTS, GUARANTEES, OR WARRANTIES, EXPRESS OR IMPLIED, RELATED
TO THE EVALUATION BOARD INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTY OF MERCHANTABILITY, TITLE, FITNESS FOR A PARTICULAR PURPOSE OR NONINFRINGEMENT OF INTELLECTUAL
PROPERTY RIGHTS. IN NO EVENT WILL ADI AND ITS LICENSORS BE LIABLE FOR ANY INCIDENTAL, SPECIAL, INDIRECT, OR CONSEQUENTIAL DAMAGES RESULTING FROM CUSTOMER’S POSSESSION OR USE OF
THE EVALUATION BOARD, INCLUDING BUT NOT LIMITED TO LOST PROFITS, DELAY COSTS, LABOR COSTS OR LOSS OF GOODWILL. ADI’S TOTAL LIABILITY FROM ANY AND ALL CAUSES SHALL BE LIMITED TO THE
AMOUNT OF ONE HUNDRED US DOLLARS ($100.00). EXPORT. Customer agrees that it will not directly or indirectly export the Evaluation Board to another country, and that it will comply with all applicable
United States federal laws and regulations relating to exports. GOVERNING LAW. This Agreement shall be governed by and construed in accordance with the substantive laws of the Commonwealth of
Massachusetts (excluding conflict of law rules). Any legal action regarding this Agreement will be heard in the state or federal courts having jurisdiction in Suffolk County, Massachusetts, and Customer hereby
submits to the pers onal jurisdiction and venu e of such courts. The United Nations Conventi on on Contracts for the Internation al Sale of Goods shall not apply to this Agreement and is expressly disclaimed.
©2010 Analog Devices, Inc. All rights reserved. Trademarks and
registered trademarks are the property of their respective owners.
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