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Table of Contents
EVAL-CN0429-EBZ Overview
Boards Used
Features
Documents Needed
Equipment Required
Test Setup Functional Block
Diagram
Hardware Setup
Connecting the
Electrochemical Gas Sensor
Temperature & Humidity
Sensor
Connector P1
Switch Configurations
Software Setup
Setting up the Serial
Terminal Software to
Communicate with the
Boards
Example of System Setup
Programming the CN0429
IDE Setup
Command Line Interface (CLI)
Getting Started
CLI Command Set
Select the Sensor
Sensor Configuration
Reading Sensor Data
Sensor Diagnostics
Schematic, PCB Layout, Bill of
Materials
Software
This version (06 Dec 2018 15:29) was approved by MRaninec.
The Previously approved version (03 Dec 2018 17:33) is available.
EVAL-CN0429-EBZ Overview
Gas detection instruments are used in a wide range of applications ranging from home air quality
measurement devices to industrial solutions for detecting toxic gases. Many of these instruments use
electrochemical gas sensors. This sensor technology requires specialized front-end circuitry for
biasing and measurement.
By utilizing built-in diagnostics features (such as impedance spectroscopy or bias voltage pulsing and
ramping) it is possible to inspect sensor health, compensate for accuracy drift due to aging or
temperature, and estimate the remaining lifetime of the sensor right at the edge of the sensor network
without user intervention. This functionality allows smart, accurate sensor replacement at the
individual edge nodes. An integrated, ultra low power microcontroller directly biases the
electrochemical gas sensor and runs onboard diagnostic algorithms.
The CN0429 circuit shows how an electrochemical gas sensor is connected to the potentiostat
circuit and how it is biased and measured. Common 2-lead, 3-lead, and 4-lead electrochemical gas
sensors can be used interchangeably. The integration of this signal chain dramatically reduces cost,
size, complexity, and power consumption at the sensor node.
Boards Used
Following are the boards used:
EVAL-M355-ARDZ-INT Arduino Shield Board
EVAL-ADICUP3029 Board
EVAL-CN0429-EBZ Gas Sensor Daughter Board
Features
Capable of measuring any electrochemical gas sensor in a suitable package
Up to 4 sensor boards can be connected for measurements simultaneously
Gas sensor daughter boards includes temperature & humidity sensor
Electrochemical Impedance Spectroscopy and Bias Voltage Pulse Test capabilities
Documents Needed
ADuCM355 Data Sheet
CN0429 Circuit Note
EVAL–ADICUP3029 User Guide
Equipment Required
Hardware
EVAL-CN0429-EBZ Gas Sensor Daughter Board
EVAL-ADICUP3029 Base Board
EVAL-M355-ARDZ-INT Interposer Board
Micro USB Cable
Electrochemical Gas Sensor in a suitable form factor
Software
PC with a USB port and Windows 7 (32-bit) or higher
Serial Terminal Software (Putty/TeraTerm or similar)
3-Terminal or 4-Terminal Electrochemical Gas Sensor
Test Setup Functional Block Diagram
To set up the circuit for evaluation, consider the following steps:
1. The EVAL-CN0429-EBZ ( CN0429 Shield board) connects to EVAL-M355-ARDZ-INT interposer board
2. That combination setup above, plugs directly into the EVAL-ADICUP3029 base board
3. Connect the system to the PC using USB cable
4. Connect the sensors to the dedicated connectors on the EVAL-CN0429-EBZ
Hardware Setup
Connecting the Electrochemical Gas Sensor
The CN0429 is compatible with electrochemical gas sensors in “4-series” form factor. 2-, 3- and 4-electrode sensors are supported. See the
drawing below for form factor dimensions.
Examples of sensors supported by this reference design:
CiTicel® 4CF+
Alphasense CO-A4
DD Scientific GS+4CO
Temperature & Humidity Sensor
The CN0429 gas sensor daughter board includes IDT HS3002 temperature & humidity sensor. This sensor is connected to a virtual I2C bus of
the ADuCM355 microcontroller. Temperature and humidity values could be used to implement compensation techniques for an electrochemical
gas sensors. For more information about how to obtain sensor data, please refer to the Software section.
add link to Software section here
Connector P1
Connector P1 is used for interfacing with the CN0429 board. It is used to provide power to the board and also to communicate with it using I2C,
SPI or UART interfaces. There is also one GPIO available, which can be used as an interrupt input to wake-up the ADuCM355 or provide any
other interrupt function.
P1 connector pinout
The connector used on the CN0429 board is Samtec SFM-107-02-L-D. The mating connector for it is either TFM-107-02-L-D (surface mount)
or TFM-107-01-L-D (through hole).
Switch Configurations
Switch Configuration for EVAL-M355–ARDZ–INT Arduino Shield Board
There as two switches present on the EVAL-M355–ARDZ–INT board, namely switches S1 and S2.
Switch S1 selects which channel on the EVAL-M355-ARDZ-INT that is currently programmable. THis is only needed/used when flashing
custom firmware onto the EVAL-CN0429-EBZ
Switch S2 selects the communication method when SPI(default communication method) is not being used. So UART and I2C are
possible communcation modes back to the processor, as long as the firmware on the EVAL-CN0429-EBZ is set accordingly.
Switch Configurations for EVAL–ADICUP3029 Board
There are 5 switches present on the EVAL–ADICUP3029 board, namely switches S1, S2, S3, S4 and S5.
Switch S2 routes the UART signals (Tx/Rx) from the ADuCM3029 and has three(3) options, ' USB', 'Arduino' and 'WiFi. While in USB
mode, the board communicates UART over the USB with the PC. This is the recommended setting for water quality measurements.
When the switch is on Arduino mode, it establishes a UART communication with the Arduino connects on the ADICUP3029. WiFi mode
allows the user to communicate with the plugin WiFi module available with the ADICUP3029.
Switch S5 selects the power source and has two(2) options, 'Wall/ USB' and 'Battery'. These options allows the user to choose between
powering the board using USB/DC wall supply (choosing Wall/ USB on switch S5) or using 2 AAA Batteries (choosing Batt on switch S5).
Switch S1 is a reset switch, used to reset the board.
Switch S3 is a boot switch, used to reboot the board by pressing the reset and boot switch together.
Switch S4 is a WiFi reset switch, used to reset the externally connected WiFi board.
Software Setup
Setting up the Serial Terminal Software to Communicate with the Boards
The EVAL-CN0429-EBZ board and EVAL–ADICUP3029 board come with a pre-installed base code. The user needs to install a serial
terminal software on their PC to communicate with the board. The recommended software is PuTTY which is easily available over the internet for
free installation. Once PuTTY is installed, user needs to go to the Device Manager terminal through the Start option in Windows. The Device
Manager terminal opens as follows:
The new options that appear in the Device Manager window, as shown in the picture above, shows that the PC has detected the EVAL–
ADICUP3029 board. The user is then advised to note the port number of the USB Serial Device (COM5 as seen above). With a right click on the
USB Serial Device (COM5), the user can then access the properties of the board connected. Note the speed shown here is 115200.
Once these steps have been followed, the user can now to start the PuTTY application and enter certain values in the configuration window. The
three important settings that needs to be defined in the configuration window are the Session settings, the Terminal settings and the Serial
settings. In the Session window, the speed should be set at 115200 and the serial line is the port number taken from Device manager (COM5 in
our case).
The user can save these settings by a particular name (we call it WaterQual_ADICUP3029) and load them whenever needed. Other important
configurations include the terminal settings and the connection serial settings. They should be set as follows before launching the Putty
application:
Once all the configurations have been defined, launch the PuTTY terminal by selecting the 'Open' option. After the PuTTY terminal launches,
write 'help' ane press Enter to see the different commands in the PuTTY terminal for various gas measurements. See the Command Line
Interface section for more details.
Example of System Setup
In this section, step by step instructions are provided to configure the system and the sensor for correct operation. It is recommended to always
use this procedure.
Preparing the system
1. Plug the EVAL-M355-ARDZ-INT board into the EVAL-ADICUP3029 board.
2. Plug the EC sensor to the EVAL-CN0429-EBZ board.
3. Plug the EVAL-CN0429-EBZ board with EC sensor to any of the four positions on the EVAL-M355-ARDZ-INT board
4. Connect the assembled system to the PC with MicroUSB cable.
5. Open PUTTY serial terminal, set the COM port to 115200 8N1 configuration, and enable forced local echo.
6. Connect to the board using PUTTY terminal.
7. Press the RESET switch on the EVAL-ADICUP3029 board. It is under the EVAL-M355-ARDZ-INT board, but reachable.
8. Observe initialization messages of the system in PUTTY terminal window.
9. Once initialized, you can start using the system.
The EVAL-CN0429-EBZ boards come pre-programmed and pre-configured. Sensor configuration needs to be modified according to the
datasheet of the sensor used. Refer to the Sensor Configuration section for more details.
Programming the CN0429
The Eval-CN0429-EBZ board comes with a pre-loaded base code. However if the user wishes to modify the firmware for custom
measurements, they need to download and install IAR ARM 8.30.2 (or above) workbench. Along with this the user also needs to download the
ADuCM355 support package, cut traces for the Serial Wire Debug (SWD) line and use the included cable to connect the debugger to the shield
board.
IDE Setup
1. Install IAR Embedded Workbench for ARM
Please visit https://www.iar.com/ to download IAR Embedded Workbench for ARM (version 8.30.2 or above)
2. License Installation
Once downloaded, the IAR window pops up as shown below. To activate the IAR workbench, click on the help tab.
Then select the License Manager option. This will open a tab asking the user to register for a license key.
When the user clicks on register, they are redirected to IAR website wherein they need to fill out their details to get access to a license
number. Upon filling up the details, the user will receive a license number which has to be entered back in the tab above then hit Next.
This completes the IAR setup and the user can validate their IAR license by looking at this window that pops up in the License Manager
option now.
The user now needs to load the ADuCM355 support package and modify the code by reprogramming it. After cutting the traces and
programming the boards, the cable needs to be connected to the EVAL-ADICUP3029 board again to allow USB communication.
Command Line Interface (CLI)
Getting Started
The CN0429 reference design is controlled using a command line interface. Any serial port terminal application can be used, e.g. Putty,
TeraTerm. Configure the COM port to 115200/8N1 (115200 baud, 8 data bits, no parity bit and 1 stop bit). Once the system is programmed and
connected to the PC, connect to it using the serial terminal application of your preference. The system is automatically initialized upon power-up
and will print initialization report (example below).
Note: The gas sensor daughter boards require ~10 seconds to calibrate and start up properly. It is recommended that ~10 seconds after power
is applied to the system, the RESET button S1 is pressed on the ADICUP3029 board to ensure proper initialization of the system.
CLI Command Set
The following table lists all available commands for the CN0429. Some of the commands are global – meaning they are applicable to all detected
sensors at once. Others require user to first select a sensor and the command will then be used for the selected sensor only.
Syntax Parameter Description Usage
help Print command set help. GLOBAL
defaultsensor = 1 – 4 Select sensor site used by local commands.
sensorsconnected Print list of detected sensors.
readconfigs Read configuration of all sensors.
readsensors Read sensor data of all sensors.
setupdaterate = 1 – 3600 Set update rate for “readsensors” in seconds. Default = 1.
stopread Stop sensor data reading.
readtemp Read temperature from the on-board temperature sensor. LOCAL
Sensor site
needs to be
selected
prior to
using these
commands
readhum Read humidity from the on-board humidity sensor.
setmeastime = 50 - 32000 Set ADC sampling time in milliseconds. The ADC performs average of
10 samples at configured interval Default = 500.
startmeas Start ADC sampling at configured interval.
stopmeas Stop ADC sampling the sensor.
setrtia = 0 - 26 Select internal RTIA resistor to set TIA gain.
setrload = 0 - 7 Select internal RLOAD resistor for the sensor.
setvbias = -1100 – 1100 Set bias voltage of the sensor in mV.
setsensitivity = nA/ppm Set sensor sensitivity in nA/ppm.
runeis Run Electrochemical Impedance Spectroscopy test (EIS).
readeis Read results of EIS test.
readeisfull Read full set of results of EIS test, including all impedances and
magnitudes.
readrcal Read value of internal 200R calibration resistor.
runpulse Run the pulse test. Amplitude and Duration need to be set first!
readpulse Read results of the pulse test.
pulseamplitude = 1 – 3 Pulse test amplitude in mV (typically 1 mV).
pulseduration = 1 - 199 Pulse test duration in milliseconds. Must be less than 200 msec.
Select the Sensor
To be able to use any local command, a sensor needs to be selected first. Use following command to list all available (detected) sensors.
sensorsconnected
Afterwards, select the desired sensor, for example using:
defaultsensor 1
This command selects the sensor site. When using local commands, these apply to the selected site only. When no sensor site is selected, or
there is no sensor connected at the selected site, an ERROR message will be displayed when trying to execute a local command.
Sensor Configuration
The ADuCM355 firmware comes with pre-programmed default gas sensor configuration. In order for the sensor to work correctly, this
configuration needs to be changed according to the sensor specification which can be found in the sensor datasheet. Following configuration
parameters need to be set using the command line interface:
Bias voltage [ mV]
Sensor sensitivity [nA/ppm]
RTIA [ohm]
RLOAD [ohm]
Measurement time [msec]
Note: Select the correct sensor site prior to using any of the following commands.
Bias voltage
Bias voltage is the voltage applied between RE and WE (SE) electrode of the gas sensor. Its value can be found in the sensor datasheet.
Example: setting bias voltage to 20 mV
setvbias 20
Sensor sensitivity
Sensor sensitivity value is used to calculate the gas concentration from the measured current produced by the sensor. If the sensor datasheet
only states a range of currents instead of an exact value, please contact the sensor manufacturer and ask for more accurate value.
Example: setting setsensitivity to 73 nA/ppm
setsensitivity 73
TIA Gain - RTIA
The RTIA resistor value should be selected so that it maximizes the ADC input range of ±900 mV. The RTIA value is calculated using following
equation:
where:
0.9 V is ADC input range,
Sensitivity is defined as nA/ppm and
Max_Range is the sensor’s maximum range in ppm.
From the table below, select the closest lower value to the calculated RTIA value.
value 0 1 2 3 4 5 6 7 8
Resistor [ohm] 0200 1k 2k 3k 4k 6k 8k 10k
value 910 11 12 13 14 15 16 17
Resistor [ohm] 12k 16k 20k 24k 30k 32k 40k 48k 64k
value 18 19 20 21 22 23 24 25 26
Resistor [ohm] 85k 96k 100k 120k 128k 160k 196k 256k 512k
Example - CO sensor:
Sensitivity = 73 nA/ppm
Max_Range = 500 ppm
Closest lower value to 24.7 kΩ is 24 kΩ, i.e. = 12 .
setrtia 12
Load Resistor - RLOAD
The load resistor value can be obtained from the sensor datasheet. If there is no exact match between the datasheet value and table below,
select the closest value.
value 0 1 2 3 4 5 6 7
Resistor [ohm] 010 30 50 100 1k6 3k1 3k6
Example - CO sensor:
Datasheet value is 47 Ω. The closest available value is 50 Ω:
setrload 3
Measurement Time
The EC sensor is sampled by the ADC with a certain time period, at which it performs an average of 10 samples, each 2.2 ms long. Default value
of this time period is 500 ms, but can be configured to in the range of 50 - 32 000 ms.
Example: setting measurement period to 1000 ms
setmeastime 1000
Reading Sensor Configuration
Once the configuration has been performed, use the readconfigs command to verify that configuration is complete. This command reads
configuration of all detected sensors.
readconfigs
Reading Sensor Data
Once all the sensors are configured, sensor data can be obtained. Temperature and humidity data from on-board sensor can be read one value
at a time with dedicated commands. Gas data are read as a continuous stream with configurable update rate.
Start ADC sampling
This local command instructs the ADC of selected sensor to start sampling the sensor at the time interval configured by the setmeastime
command.
startmeas
Note: It is not needed to run this command as a part of sensor initialization. ADC sampling starts automatically, default value of 500 ms is used.
Stop ADC sampling
This local command instructs the ADC of selected sensor to stop sampling the sensor.
stopmeas
Start reading gas sensor data
Use this global command to start reading gas sensor data from all sensors.
readsensors
The data is read back as a continuous stream in a following format:
Stop reading gas sensor data
Data stream can be stopped at any time using the stopread command.
stopread
Set stream update rate
The update rate of the data stream is configurable in the range of 1 – 3600 seconds. Stop the data stream before using this command.
Example: setting update rate to 5 seconds
setupdaterate 5
Read temperature
This local command prints temperature value from the temperature & humidity sensor on gas sensor daughter board.
readtemp
Read humidity
This local command prints humidity value from the temperature & humidity sensor on gas sensor daughter board.
readhum
Sensor Diagnostics
This reference design supports two diagnostics measurements of electrochemical sensors:
Electrochemical Impedance Spectroscopy (EIS)
Bias voltage pulse test
Electrochemical Impedance Spectroscopy
The EIS test is a diagnostics method where sensor impedance is measured at various frequencies of AC signal injected into the electrochemical
sensor itself. The default set of frequencies supported by the sensor daughter board firmware is:
1kHz, 5kHz, 10kHz, 20kHz, 30kHz, 40kHz, 50kHz, 60kHz, 70kHz, 90kHz, 160kHz and 200kHz.
Note: It is possible to add additional frequencies to the EIS test. However, this has to be accounted for in both gas sensor daughter board
firmware and ADICUP3029 firmware.
The test is executed by following these steps:
1. Run the EIS test ( runeis)
2. Wait for at least 5 seconds until the test is finished
3. Read the test results ( readeis)
runeis
readeis
The results of the EIS test are in a format shown below. The values are comma delimited to enable importing the data to Microsoft Excel or similar
tool for further processing.
Bode magnitude and Bode phase values are printed for every measured frequency.
To obtain full set of results including all magnitudes and impedances, use the following command:
readeisfull
Bias voltage pulse test
This diagnostics method can be used, for example, to detect open circuit, i.e. unplugged sensor. This proved to be a common issue with some
portable instruments which can fall on the ground and sensor can disconnect from its socket.
The principle of this test is applying small voltage pulse (typically 1 mV for <200 ms) to the sensor electrodes and measuring the current
response to this pulse.
Test execution procedure follows these steps:
1. Set pulse amplitude ( pulseamplitude)
2. Set pulse duration ( pulseduration)
3. Run the pulse test ( runpulse)
4. Wait for at least 5 seconds
5. Read the test results ( readpulse)
Example: setting pulse amplitude to 1 mV
pulseamplitude 1
Example: setting pulse duration to 100 ms
pulseduration 100
runpulse
readpulse
The example below shows portion of the pulse test results. The values are comma delimited to enable importing the data to Microsoft Excel or
similar tool for further processing.
Schematic, PCB Layout, Bill of Materials
EVAL-CN0429-EBZ Design & Integration Files
Schematics
PCB Layout
Bill of Materials
Allegro Project
Software
CN0429 ADuCM355 Source Code
CN0429 ADICUP3029 Source Code
End of Document
resources/eval/user-guides/circuits-from-the-lab/cn0429.txt · Last modified: 06 Dec 2018 12:44 by MRaninec
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