Circuits from the Lab ^® reference design

The Circuits from the Lab ^® Reference Design is a solution that includes performance evaluation reports as well as all design information, including boards and layouts, software, and so on, that were created by experienced Analog Devices engineers with the aim of producing end products in various fields.

Circuit from the Lab (CFTL) will contribute to the performance examination, reduction in time / cost of customer-like projects, as in the in-house prototyped and evaluation reports.
The Circuits from the Lab reference design provides you with the following resources.

⦁    Comprehensive documentation including performance evaluation
⦁    All design data, including BOM, Garber data, and software
⦁    Factory-tested hardware

This article provides a reference design for a water quality measurement system.

Features of CN0428 Water Quality Measurement System

The detection of electrochemical methods for liquid analytical measurements, such as pH, requires the design of an analog front end for each sensor, while there is a growing need for the market to obtain information on multiple parameters in real time.

The CN0428 Water Quality Measurement System is a complete measurement platform that meets the size, cost, and power requirements of a sensor installation. The circuit is small enough to be mounted on the back of the sensor and works with a variety of sensor types. Integrated measurement capabilities are available to improve the reliability of the primary measurement. In addition, the circuit provides a health check that can reduce system maintenance costs.

The CN 0428 water quality measurement system has the following 3 major features.

1.    Interposer board enables measurement with up to 4 sensors
2.    Multiple electrochemical parameters can be measured by firmware selection.
3.    Microcomputer with a built-in high-precision analog front end integrated for an electrochemical sensor 

Interposer board enables measurement with up to 4 sensors

CN 0428 water quality measurement system consists of the following boards.

⦁    EVAL-CN0428-EBZ：sensor board
⦁    EVAL-M355-ARDZ-INT：Arduino-compatible interposer
⦁    EVAL-ADICUP3029：Arduino-compatible form factor

EVAL-M355-ARDZ-INT can operate up to 4 sensor boards simultaneously. 

EVAL-ADICUP3029 uses ADI's Arm® Cortex® - ADICUP ultra-low-power microcomputer ADuCM3029 and CrossCore Embedded Studio, an open source Eclipse-based development environment.
CrossCore Embedded Studio includes many examples of hardware and software projects, making it easy to prototype and develop connectivity systems and solutions for IoT applications.

CN0428 Water quality measurement system block diagram

Image of water quality measurement system CN0428 connection

Multiple electrochemical parameters can be measured by firmware selection

CN0428 water quality measurement system supports the following measurement methods by selecting firmware.

• Electrochemical impedance spectroscopy (EIS)
• Current measurement
• Multi-step amperometry (MA)
• Chronoamperometry
• Pulse amperometry (PAD)
• Fast Current Measurement (FAM)
• Zero resistance ammeter (ZRA)

 Voltammetry

• Linear sweep voltammetry (LSV)
• Differential perspotensiometria (DPV)
• Square wave voltammetry (SWV)
• Normal pulse voltammetry (NPV)
• AC voltammetry (ACV)
• Cyclic voltammetry (CV)

Microcomputer with a built-in high-precision analog front end integrated for an electrochemical sensor 

CN0428 Water Quality Measurement System uses an integrated analog front-end microcomputer and high-precision amplifier from ADI. CN0428 Water Quality Measurement System provides an easy way to test the functionality and characteristics of these high-performance devices.

・ADUCM355：High-Precision analog microcontroller with a chemical sensor interface
・LTC6078：Low input bias current amplifier

You can download the various data of CN0428 water quality measurement system from the below URL link.
https://www.analog.com/jp/design-center/reference-designs/circuits-from-the-lab/cn0428.html#rd-overview

Target Applications

• Measurement equipment
• Scientific equipment
• Process monitoring
• Liquid analysis and water quality measurement in food and beverages, power generation, drinking-water, wastewater treatment, etc.

Product description

The features of ADUCM355

Analog input and output

• 16 bit, 400 ksps ADC
• Ability to measure voltage, current, and impedance
• Internal / external current and voltage channels
  • Ultra-low voltage leakage switch-matrix and input multiplex communication circuit
  • Input buffer, programmable gain amplifier

Voltage DAC

• Dual output VDAC: 2
  • Output range 0.2 V ～ 2.4 V (±2.2 V voltage potential to sensor) for 12-bit outputs
  • Two bias potentiostat and TIA amplifiers
    Ultra-low power consumption : 1 μA per amplifier
• High-speed 12 bit VDAC: 1
  • Sensor output range：±607 mV
  • High-speed TIA for impedance measurement
  • Programmable gain amplifier for output

Amplifiers, Accelerators and References

• 2 Low power consumption, low noise amplifiers
  • Suitable for constant potentiostat bias in electrochemical sensing
• 2 Low power consumption, low noise TIAs
  • Suitable for measuring sensor current output ±0.00005 μA to ±3000 μA range
  • Programmable Load and Gain Resistance
• Analog hardware accelerator
  • DDS waveform generator
  • DFT and digital filters
• 2.5 v and 1.82 v on-chip, high precision voltage reference
  Accurate internal temperature sensor at ±2℃
  <Impedance measurement range from < 1Ω10MΩ, 0.016Hz to 200kHz
  Voltammetric scan rates up to 2,000 steps in 1 second

Microcontroller

• 26 MHz ARM Cortex-M3 processor
• Serial wire port supports code download and debugging
• 128 kB Flash／64 kB SRAM
  Safety and security
• Hardware encryption with AES-128 and AES-256
• Hardware CRC with programmable polynomial generator
• User flash read / write protection

On-chip peripherals

• UART, I2C, and SPI serial input / output
• Up to 17 GPIO pins
  • External interrupt option
  • General-purpose, wake-up, and watchdog timers

Power

• Power supply and effective measurement range：2.8 V～3.6 V
• Power monitor
• Effective current consumption of the digital section 30μA/MHz
• Hibernate with bias to external sensor : 8.5μA

Package and temperature range

• 6 mm × 5 mm、72 pin LGA package
• Specifications for peripheral operation of −40℃ ～ +85℃

The features of LTC6078

• Maximum offset voltage：25μV (25℃)
• Maximum offset drift：0.7μV/℃
• Maximum input bias current：
  • 1pA（25℃）
  • 50pA（85℃ or less）
• Micro power： 54μA/amplifier
• CMRR：95dB (minimum)
• PSRR：100dB (minimum)
• Input noise voltage：16nV/√Hz
• Rail-to-rail input / output
• 2.7V～5.5V operating voltage
• 8 pin MSOP and 10 pin DFN packages