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Volatile Organic Compounds (VOC) Measurement Demo

The ADuCM360_demo_cn0395 is a volatile organic compounds (VOC) detector demo project for the EVAL-ADICUP360 base board with additional EVAL-CN0395-ARDZ shield, created using the GNU ARM Eclipse Plug-ins in Eclipse environment.


General description


This project is a good example for how to use EVAL-ADICUP360 board in different combinations with various shield boards. It expand the list of possible applications that can be done with the base board.

The ADuCM360_demo_cn0395 project uses the EVAL-CN0395-ARDZ shield which is a portable VOC detector which comes with a Figaro TGS8100 MOX sensor.



The TGS8100 sensor requires two voltage inputs: heater voltage (VH) and circuit voltage (VC). The heater voltage (VH) is applied to the integrated heater in order to maintain the sensing element at a specific temperature which is optimal for sensing. The EVAL-CN0395-ARDZ shield circuit provides the heater voltage (VH), by using ADN8810 IDAC as a programmable current source. The default full scale current in the IDAC is 9.94mA and the default value of the RSN resistors is 41.2Ω.

The hardware also allows for two main modes of operation: heater mode and sensor resistance measurement mode. In heater mode, the AD7988-1 ADC receives as input the heater voltage (VH) while in sensor mode the input is the voltage from the sense circuit (VRS). The switching is done by using ADG884. The full scale voltage measured by the ADC is 4.096 V.

Moreover, the hardware includes a gain select circuit which can add additional overlapping ranges if needed when performing a resistance sensor measurement. ADG758 8-channel multiplexer is used to accomplish this task.

TGS8100 sensor has a temperature and humidity dependency, therefore temperature compensation is performed. The ADuCM360_demo_cn0395 shield includes a temperature and humidity sensor (Sensirion SHT-30), which operates on I2C bus.

The ADuCM360_demo_cn0395 uses a UART interface (9600 baud rate and 8-bits data length), as a command line interpreter, to send the results to terminal window. Beside the interpreter processes several commands.

Demo Requirements

The following is a list of items needed in order to replicate this demo.

  • Hardware
    • EVAL-ADICUP360
    • EVAL-CN0395-ARDZ
    • Mirco USB to USB cable
    • PC or Laptop with a USB port
  • Software
    • ADuCM360_demo_cn0395 software
    • CrossCore Embedded Studio (2.7.0 or higher)
    • ADuCM36x DFP (1.0.2 or higher)
    • CMSIS ARM Pack (4.3.0 or higher)
    • Serial Terminal Program
      • Such as Putty or Tera Term

Setting up the hardware

  1. To program the base board, set the jumpers/switches as shown in the next figure. The important jumpers/switches are highlighted in red.
  2. Connect the EVAL-CN0395-ARDZ to the Arduino connectors P2, P5, P6, P7, P8 of the EVAL-ADICUP360 board.
  3. Plug in the USB cable from the PC to the EVAL-ADICUP360 base board via the Debug USB.(P14)

Obtaining the source code

We recommend not opening the project directly, but rather import it into CCESand make a local copy in your workspace.

The source code and include files of the ADuCM360_demo_cn0395 can be found on Github:


CrossCore Embedded Studio Application Source Code:

AduCM360_demo_cn0395 at Github

For more information on importing, debugging, or other tools related questions, please see the tools user guide.

Configuring the Software Parameters

There are no configurations needed for this demo example.

Outputting Data

Serial Terminal Output

  1. In order to view the data, you must flash the program to the EVAL-ADICUP360.
  2. Once complete you will need to switch the USB cable from the DEBUG USB (P14) to the USER USB (P13).
  3. Then follow the UART settings below with the serial terminal program.


Following is the UART configuration.

  Select COM Port
  Baud rate: 9600
  Data: 8 bit
  Parity: none
  Stop: 1 bit
  Flow Control: none


The application allows the user to select between the two modes of operation:

  • Heater mode (RH)
  • Sensor Resistance mode (RS)

Heater Mode (RH)

The user can further choose the subroutine which determines the heater current (IH):

voltage is the routine for setting heater voltage to constant voltage VH (the default value is VH = 1.8V). The relationship between heater resistance RH and heater current IH or heater voltage VH is nonlinear. Therefore the software runs in background several iterations in order to get VH to the desired accuracy with a 0.5% max error.

resistance is the routine for setting the heater resistance to constant resistance RH (the default is RH = 225Ω). For a heater resistance RH, set IH = (RH – 110Ω)/14375 [Note: The slope of the RH vs. IH curve is 115Ω/8mA = 14375Ω/A]. The software runs in background several iterations in order to get RH to the desired accuracy with a 0.5% max error.

temperature is the routine of setting the heater temperature to constant temperature TH (the default is TH = 360 C). This is done in three steps:

  1. The desired heater resistance RH_T is computed from RH_T = RH_A [ 1 + ALPHA*(RH_0/RH_A)*(T – T_A)], where:
    • RH_A is the heater ambient temperature (measured at power up)
    • RH_0 is the default heater resistance (110Ω @ 20°C)
    • T is the desired heater temperature (user input)
    • T_A is the ambient temperature (measured at power up)
    • ALPHA is the constant 0.003074
  2. The resulted RH is used to calculate IH and VH with constant resistance routine.
  3. The resulted VH is further adjusted by using the constant heater voltage routine.

current simply sets the IDAC to the desired current.

After the completion of the routine, the application displays the measured values: RH_A (Ambient Heater Res ), VH (heater voltage), IH (heater current), RH (heater resistance), T_A (ambient temperature), HUM (ambient humidity), PH (heater power consumption), TH (heater temperature), ADC data (raw data read from ADC in hex), Ro ( sensor resistance measured in clean air).

At power up, the application starts in constant current mode and sets the default current to 8mA. Furthermore, it is assumed that the measurement circuit is placed in clean air, therefore we measure and store the sensor resistance in clean air (Ro). After each heater measurement mode change, it is assumed that the board is placed in clean air, and the Ro value is updated. This is required, because Ro is a function of the heater temperature.

Sensor Resistance mode (RS)

Sensor measurement is performed. The application can switch at any time to this mode by pressing the <ENTER> key. The AD7988-1 ADC receives the voltage from the sense circuit (VRS). The switching is done by using ADG884.

In background every time the application runs the gain-ranging algorithm and determines RS and the gas concentration (C) measured in PPM (parts per million):

RS reading can also be performed by typing <operation RS>, but it does the same thing as pressing the <ENTER> key.

Factory Calibration The IDAC current from the ADN8810 is 1% accurate, therefore a factory calibration must be performed. The routine loads code 4095 into ADN8810 and reads the ADC, which ideally should be 9.94mA × 71.5Ω = 0.71V, or code [0.71/4.096] x 65,535 = 11,360. The gain correction factor k1 = 11,360/CODEFS. It is recommended that this is done only once. Follow the procedure:

  1. Type <calibrate w>
  2. Connect jumper P2 between P2-1 and P2-2, this connects the IOUT to the precision 71.5Ω resistor.
  3. Press <c> key when ready
  4. Power Off → On

From this point on, K1 is stored in permanent memory and applied to currents that are input. To read the gain correction factor from memory, type <calibrate r>.

Help

Type <help> to see the available commands:

How to use the Tools

The official tool we promote for use with the EVAL-ADICUP360 is CrossCore Embedded Studio. For more information on downloading the tools and a quick start guide on how to use the tool basics, please check out the Tools Overview page.

Importing

For more detailed instructions on importing this application/demo example into the CrossCore Embedded Studios tools, please view our How to import existing projects into your workspace section.

Debugging

For more detailed instructions on importing this application/demo example into the CrossCore Embedded Studios tools, please view our How to configure the debug session section.

Project structure


The ADuCM360_demo_cn0395 project use ADuCM36x C/C++ Project structure.

This project contains: system initialization part - disabling watchdog, setting system clock, enabling clock for peripherals; port configuration for SPI1, UART via P0.6/P0.7, I2C via P2.0/P2.1; SPI, UART, I2C read/write functions; Flash read/write functions, AD7988 control, ADN8810 control, SHT30 control and VOC concentration computation.

In the src and include folders you will find the source and header files related to CN0395 software application. The Communication.c/h files contain SPI, UART and I2C specific data, the AD7988.c/h files contain the ADC control, the ADN8810.c/h files contain the IDAC control, the SHT30.c/h files contain the temperature/humidity sensor control, the Flash.c/h files contain helper functions to read/write to the permanent memory, and the CN0395.c/h files contain commands, configurations and computations specific to the VOC detector application.


The RTE folder contains device and system related files:

  • Device Folder – contains low levels drivers for ADuCM360 microcontroller.(try not to edit these files)
  • system.rteconfig - Allows the user to select the peripherial components they need, along with the startup and ARM cmsis files needed for the project.



End of Document

/srv/wiki.analog.com/data/pages/resources/eval/user-guides/eval-adicup360/reference_designs/demo_cn0395.txt · Last modified: 21 Feb 2019 01:22 by WassimB