EVAL-CN0363-PMDZ

Overview

The EVAL-CN0363-PMDZ 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 via a standard PMOD connector to a FPGA. 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.

A clock set to a user-programmable frequency modulates one of the three LED colors (R,G,B) with a constant current driver built around the AD8615 op amp, the ADG819 switch, and the AD5201 digital potentiometer. The beam splitter sends half the light through the sample container and half through the reference container. The ADA4528-1, configured as a transimpedance amplifier, then converts the photodiode current into an output voltage square wave, whose amplitude is proportional to the light transmitted through the sample or reference containers. The transimpedance amplifiers use the ADG633 single-pole, double-throw (SPDT) switches to select one of two transimpedance gains. The AD7175-2 Σ-Δ ADC samples the voltage and sends the digital data to an FPGA for digital demodulation.

Features:

  • Dual-channel colorimeter with synchronous detection

  • Modulated light source with three LED colors (R, G, B)

  • Programmable gain transimpedance amplifiers on each channel

  • Very low noise, 24-bit sigma-delta ADC (AD7175-2)

  • FPGA-based digital synchronous demodulation

  • Standard PMOD connector for FPGA interface

  • Ratiometric measurement (sample vs. reference)

Applications:

  • Chemical analysis

  • Environmental monitoring

  • Absorption spectroscopy

https://media.githubusercontent.com/media/analogdevicesinc/documentation/main/docs/solutions/reference-designs/eval-cn0363-pmdz/images/colorimeter_photo.png

For a thorough circuit description, please visit CN0363 Circuit Note.

Recommendations

People who follow the flow that is outlined have a much better experience with things. However, like many things, documentation is never as complete as it should be. If you have any questions, feel free to ask on our EngineerZone forums, but before that, please make sure you read our documentation thoroughly.

Table of contents

  1. Using the evaluation board:

    1. User Guide - hardware and software guide

    2. Prerequisites - what you need to get started

    3. Quick start guides:

      1. Using the ZED Board

  2. Software:

    1. Colorimeter application

  3. Design with the EVAL-CN0363-PMDZ:

    1. CN0363 HDL project - HDL reference design

  4. Help and Support

Block diagram

https://media.githubusercontent.com/media/analogdevicesinc/documentation/main/docs/solutions/reference-designs/eval-cn0363-pmdz/images/cn0363_sch.jpg

Warning

All the products described on this page include ESD (electrostatic discharge) sensitive devices. Electrostatic charges as high as 4000V readily accumulate on the human body or test equipment and can discharge without detection. Although the boards feature ESD protection circuitry, permanent damage may occur on devices subjected to high-energy electrostatic discharges. Therefore, proper ESD precautions are recommended to avoid performance degradation or loss of functionality. This includes removing static charge on external equipment, cables, or antennas before connecting to the device.

Registration

Tip

Receive software update notifications, documentation updates, view the latest videos, and more when you register your hardware. Register to receive all these great benefits and more!