Wiki

This version (28 Jul 2017 16:24) was approved by Brandon, caugusta.The Previously approved version (26 Jul 2017 23:14) is available.Diff

EVAL-CN0395-ARDZ Shield

The circuit below is an arduino compatible, single supply 16-bit volatile organic compound detector using a metal oxide sensor. It uses ADN8810 to precisely control the current running through the sensor to get to within the 1% voltage accuracy needed for the heating element of the sensor.

CN0395 measures indoor air quality by utilizing a Metal Oxide Sensor to detect gases composed of volatile organic compounds. The sensor is composed of a heating resistor and a sensing resistor. When the sense resistor is heated its value changes as a function of the concentrations of different gasses.

Connectors and Jumper Configurations

{{:resources:eval:user-guides:eval-adicup360:hardware:cn0397:cn0397_chip_select.jpg|

Headers

P1

The current output DAC, ADN8810, has an output voltage compliance that needs to be met to maintain a linear current output. This can be done by putting a jumper on position 2 and 3 which attaches the ENCOMP pin of the part to ground for output voltages up to 2V.

For higher output voltages that 2V, tie the ENCOMP pin to +5V to maintain the output stability of the part.

P2

P2 header selects the current path from the current output DAC, ADN8810. It is populated across RH+ by default.

Silkscreen Current Path Pins
RCAL1 71.5Ω 1 & 2
RCAL1 10.0Ω 3 & 4
RH+ Heating Resistor 5 & 6

Sensor

CN0395 has the TGS8100 on board as default. Using a different set of sensors require a recalculation and replacement of the sense resistors that sets the full scale current for the device. Provision for alphasense sensors or with similar footprint is available and a screw terminal is also in place for any other types of sensors.

The calculation for the sense resistor and placement of the correct sense resistors are crucial to proper operation of the board to not violate absolute maximum ratings of the sensors

Recommended Sensors

If you are using a different sensor, you will need to wire in the appropriate signals into the board via the screw terminal (P8). This also means that you will have to remove the TGS8100 sensor that comes on the board by default. Below is a table of how to use P8 to input other sensors.

P8

Silkscreen Name Pin Number Description
RH+ Pin 1 Postive Pin of Heating Resistor
AGND Pin 2 Negative Pin of Heating Resistor
RS+ Pin 3 Postive Pin of Sensing Resistor
AGND Pin 4 Negative Pin of Sensing Resistor

Spacers

Spacers that could cater various surface mount and through hole packages are available on the board to make some modifications on the board easier.

Resistor spacers, R17_SPACER and R19_SPACER, are used to hold the sense resistors to select the maximum output current of the ADN8810. Changing these maximum output current of the ADN8810 allows the board to cater multiple types of sensor that use up to 300mA of current for measurements.

Sense resistors (RSN) can be calculated by using the formula below:

RSN= 4.096/(10* Full Scale Current)

Button

Pressing push button S2 allows the user to do a hard reset of the temperature and humidity sensor SHT30.

Schematic, PCB Layout, Bill of Materials

EVAL-CN0395-ARDZ Design & Integration Files

  • Schematics
  • PCB Layout
  • Bill of Materials
  • Allegro Project

Software

resources/eval/user-guides/eval-adicup360/hardware/cn0395.txt · Last modified: 28 Jul 2017 16:24 by Brandon