CN0216 Datasheet, PDF (4/5 Pages) Analog Devices – Devices Connected

CN-0216
Circuit Note
Figure 5. Measured Histogram for 500 Samples Showing
the Effects of Noise
COMMON VARIATIONS
Other ADCs and circuits suitable for weigh scale applications
are discussed in CN-0102 (AD7190), CN-0107 (AD7780), CN-
0108 (AD7781), CN-0118 (AD7191), CN-0119 (AD7192), and
CN-0155 (AD7195).
The AD7171 is a 16-bit sigma-delta ADC.
For a lower power consumption solution, use the ADA4051-2.
The ADA4051-2 is a dual micropower, zero-drift amplifier with
only 20 µA of supply current per amplifier.
CIRCUIT EVALUATION AND TEST
This circuit uses the EVAL-CN0216-SDPZ circuit board and
the EVAL-SDP-CB1Z system demonstration platform (SDP)
evaluation board. The two boards have 120-pin mating
connectors, allowing for the quick setup and evaluation of the
circuit’s performance. The EVAL-CN0216-SDPZ board contains
the circuit to be evaluated, as described in this note, and the
SDP evaluation board is used with the CN-0216 evaluation
software to capture the data from the EVAL-CN0216-SDPZ
circuit board.
Equipment Needed
• PC with a USB port and Windows XP or Windows Vista
(32-bit), or Windows 7 (32-bit)
• EVAL-CN0216-SDPZ circuit evaluation board
• EVAL-SDP-CB1Z SDP evaluation board
• CN0216 evaluation software
• Tedea-Huntleigh 505H-0002-F070 load cell or equivalent
• Power supply: +6 V, or +6 V “wall wart”
Getting Started
Load the evaluation software by placing the CN0216 Evaluation
Software disc in the CD drive of the PC. Using My Computer,
locate the drive that contains the evaluation software disc and
open the Readme file. Follow the instructions contained in the
Readme file for installing and using the evaluation software.
Functional Block Diagram
See Figure 1 of this circuit note for the circuit block diagram,
and the PDF file “EVAL-CN0216-SDPZ-SCH” for the circuit
schematics. This file is contained in the CN0216 Design
Support Package.
Setup
Connect the 120-pin connector on the EVAL-CN0216-SDPZ
circuit board to the connector marked “CON A” on the
EVAL-SDP-CB1Z evaluation (SDP) board. Nylon hardware
should be used to firmly secure the two boards, using the holes
provided at the ends of the 120-pin connectors. Connect the
load cell the EVAL-CN0216-SDPZ board.
With power to the supply off, connect a +6 V power supply to
the pins marked “+6 V” and “GND” on the board. If available, a
+6 V "wall wart" can be connected to the barrel jack connector
on the board and used in place of the +6 V power supply.
Connect the USB cable supplied with the SDP board to the USB
port on the PC. Note: Do not connect the USB cable to the mini
USB connector on the SDP board at this time.
Test
Apply power to the +6 V supply (or “wall wart”) connected to
EVAL-CN0216-SDPZ circuit board. Launch the evaluation
software and connect the USB cable from the PC to the USB
mini-connector on the SDP board. The software will be able to
communicate to the SDP board if the Analog Devices System
Development Platform driver is listed in the Device Manager.
Once USB communications are established, the SDP board can
now be used to send, receive, and capture serial data from the
EVAL-CN0216-SDPZ board.
Information and details regarding how to use the evaluation
software for data capture can be found in the CN0216
Evaluation Software Readme file.
Information regarding the SDP board can be found in the
SDP User Guide.
Analyzing the Data
At least 500 samples of the ADC output data should be taken.
Once the sample set is exported to a spreadsheet program, such
as Excel, the samples can be analyzed. The standard deviation of
the samples is approximately equal to the rms noise, assuming a
Gaussian noise distribution. The peak-to-peak noise is
approximately equal to the rms value multiplied by 6.6.
The peak-to-peak noise can also be taken directly from the
sample set by simply taking the difference between the largest
and smallest sample. In practice, the results obtained using this
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