CN0396 is single-supply, low noise, portable gas detector, using a 4-electrode electrochemical sensor, for simultaneous detection of two distinct gases. The Alphasense COH-A2 sensor, which detects carbon monoxide(CO) and hydrogen sulfide(H2S), is used in this example. Electrochemical sensors offer several advantages for instruments that detect or measure the concentration of many toxic gases. Most sensors are gas specific and have usable resolutions under one part per million (ppm) of gas concentration.
The circuit shown in below uses the ADA4528-2, dual auto zero amplifier, which has a maximum offset voltage of 2.5 µV at room temperature and an industry leading 5.6 µV/√Hz of voltage noise density. In addition, the AD5270-20 programmable rheostat is used rather than a fixed transimpedance resistor, allowing for rapid prototyping of different gas sensor systems, without changing the bill of materials. The ADR3412 precision, low noise, micropower reference establishes the 1.2 V common-mode, pseudo ground reference voltage with 0.1% accuracy and 8 ppm/°C drift. For applications where measuring fractions of ppm gas concentration is important, using the ADA4528-2 and the ADR3412 makes the circuit performance suitable for interfacing with a 16-bit ADC, such as the AD7790.
An ADT7310 16-Bit Digital SPI Temperature Sensor is also included in the circuit to allow for monitoring of environmental temp. This allows for correction of the temperature effects on the sensor.
The EVAL-CN0396-ARDZ Shield is designed to be compatible with the Arduino R3 shield form factor. It is compatible with either 5V or 3.3V processor boards.
Software - using ADICUP360
The evaluation board comes packaged with an Alphasense COH-A2 sensor. Sockets are already provided for easy installation of the sensor.
Pin Compatible Sensors:
Sensor Socket Connection
|WE1||Working Electrode (CO gas electrode for COH-A2 sensor)|
|WE2||Working Electrode (H2S gas electrode for COH-A2 sensor)|
Note: Not all sensors provided in this list have been tested with the EVAL-CN0396-ARDZ. Using different sensors may require modifications to the Software and/or the Hardware.
There are three(3) headers on the board allow for selection of the digital pin to be used as the Chip Select (CS) signal for the AD7798, AD5270 and ADT7310 SPI digital communications.
|AD7798_CS Connections||Arduino Pin|
|Jumper Pin 1 and Pin 2||D10|
|Jumper Pin 2 and Pin 3||D9|
|AD5270_CS Connections||Arduino Pin|
|Jumper Pin 1 and Pin 2||D6|
|Jumper Pin 2 and Pin 3||D5|
|ADT7310_CS Connections||Arduino Pin|
|Jumper Pin 1 and Pin 2||D4|
|Jumper Pin 2 and Pin 3||D3|