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CN0363 Colorimeter Application User Guide

Introduction

The circuit shown above from CN0363 is a dual channel colorimeter featuring a modulated light source transmitter, programmable gain transimpedance amplifiers on each channel, and a very low noise, 24-bit sigma delta ADC. The output of the ADC connects to a standard FPGA mezzanine card. The FPGA takes the sampled data from the ADC and implements a synchronous detection algorithm. By using modulated light and digital synchronous detection, rather than a constant (dc) source, the system strongly rejects any noise sources at frequencies other than the modulation frequency, providing excellent accuracy. The dual channel circuit measures the ratio of light absorbed by the liquids in the sample and reference containers at three different wavelengths. This forms the basis of many chemical analysis and environmental monitoring instruments used to measure concentrations and characterize materials through absorption spectroscopy.

Further details of the circuit can be found in the circuit note CN0363

A complete design support package containing schematic, assembly drawing, layout files, Gerber files, and bill-of-materials is available at CN0363-DesignSupport

Equipment Needed

The CN0363 software is designed to operate with the following hardware and FPGA development system:

ZED Board, Rev C or later
USB Keyboard/Mouse
HDMI Monitor (Full HD)
CN0363 hardware: EVAL-CN0363-PMDZ
Two vials: one filled with water and one filled with the sample liquid under test
Formatted and partitioned 8GB SD card supplied with EVAL-CN0363-PMDZ board
Ethernet connection for updating SD card

The equipment should be connected as shown below, but make sure all power is turned off before beginning the software installation.

Software Installation

An 8GB formatted and partitioned SD card is supplied with the CN0363 board. This SD card contains most of the images required to run the various FMC boards, but it must be updated before the application software for CN0363 is run. Use the following procedure:

Connect the HDMI monitor, power supply, keyboard/mouse, and Ethernet cable to the ZedBoard. Make sure the ZedBoard power switch is off.
Connect the EVAL-CN0373-PMDZ board to the ZedBoard, but do not connect the power at this time.
Install the Analog Devices SD card in the ZedBoard
Verify the jumpers (JP7-JP11, and JP6) are set to the SD Card Boot Mode as described in http://www.zedboard.org/support/documentation/1521.
Turn the ZedBoard power switch on. The board should boot after about 30 seconds.
Enter “Update” on the keyboard (Note: I'm not exactly sure if this is correct, or if you need to select something on menu first). The latest image files will be downloaded from the ADI website to the SD card. This may take some time, so don't get in a hurry.
When the update is complete, turn the ZedBoard power off.
As an alternative, the SD card can be updated using a PC with an internet connection and an SD card writer/reader. This procedure is described in Create SD Image for Zynq Boards. (it is a single image for all boards). After the SD card has been updated in the PC, install it in the ZedBoard with the power off.
Turn the EVAL-CN0363-SDPZ power on.
Turn the ZedBoard power on.
Select the “CN0363-Colorimeter” application from the menu and hit ENTER. Please correct this if incorrect
The system is now ready to analyze samples.

Source code

I think this section can be deleted

The source code for the Colorimeter application can be found on the Analog Devices GitHub account in the colorimeter repository.

Install colorimeter application

$ git clone https://github.com/analogdevicesinc/colorimeter.git
$ make
$ make install

Analyzing a Sample

The Colorimeter application has three main tabs Automated Data Collection, Current/Absorbance Measurement and the Sample Library.

Automated Data Collection

Analyze Sample

Clicking the Analyze Sample button will perform a automated sample analyzes which will cycle through all three colors and calculate the absorbence factor for each of them. The analyzing process will take a few seconds and a progress-bar will be updated to indicate the current step. Once the process has completed the absorbance values will be displayed.

Once the analyzing process has finished it is also possible to either try to match the sample to a existing sample from the sample library or save the sample into the sample library for future use.

Match Sample

Clicking the Match Sample button will compare the current sample to all samples in the sample library. If a sample is found that has a close enough matching score the sample including its name and match score will be displayed.

Save Sample

Captured data samples can be saved into the sample library for later use by clicking the Save Sample button. Samples that have been saved into the library are used in the sample matching process.

Current/Absorbance Measurement

In the Current/Absourbance Measurement tab gives direct access to the LED and gain controls and allows to periodically capture and view raw data.

On the left side are various controls that allow to change certain parameters.

Excitation Frequency: Selects the frequency of the excitation signal
Excitation Current: Selects the current of the excitation signal
LED: Selects the currently active LED. Options are None, Red, Green and Blue.
Reference Channel Gain: Selects the gain applied for the reference channel. Options are 33k Ohm and 1M Ohm.
Sample Channel Gain: Selects the gain applied for the sample channel. Options are 33k Ohm and 1M Ohm.

On the right side are three data plots. One plot each for the reference channel and the sample channel which show the measured current. And one plot for the absorbance that is derived from the currents.

Clicking the Acquire Data button below the plots will start the data capture process and the plots will be periodically update with new data. Clicking the button while the data capture process is active will stop it again.

Settings can be changed on the fly while the capture process is active to see their effect on the captured data.

Sample Library

The sample library allows to manage and compare previously saved sample data. On the left side is a list of all samples. On the right side the absorbence values for the currently selected samples is displayed. It is possible to select multiple samples by holding the Ctrl key, this can be used to directly compare the absorbance of multiple samples to each other.

Samples can also be removed from the library by selecting the sample and then clicking the Remove button. A sample that has been removed from the library can not be restored.

Calibration

For optimum performance it is necessary to calibrate the application to the connected board and the environment. This calibration can be performed in the calibration dialog which can be opened form then application's menu. It allows to set the calibration parameters the LEDs and photo-diodes as well as performing a automated calibration.

Calibration must be performed with distilled water in both the reference and the sample probes. It is also recommended that during calibration the photo-diodes are shielded from ambient light.

Start the automatic calibration procedure in the software; from the Menu bar, open the Calibration dialog box, and click Calibrate.Once the calibration is done the calibration values will be updated.

It is also possible to save the current calibration data for later use by clicking the Export button or to load previously saved calibration data by clicking the Import button.

Calibration data includes a zero-offset for each channel and gain setting, which removes any potential offset that is measured if no excitation signal is present. The calibration data also includes a gain factor which expresses the relative relationship of the reference and sample channel values at full-scale excitation.

Supported Devices

CN0363 ZED Board, Rev C or later

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