DIGILENT DIGIL 410-386 User guide

The Digilent Pmod AQS (Revision A) is a digital gas sensor for monitoring indoor air quality at low power. With theAMS

CCS811, you can detect a wide range of Volatile Organic Compounds (VOCs) using the micro-hotplate technology enables

a highly reliable solution for gas sensors with very fast cycle times.

Pmod AQS Reference Manual

Optimized low-power modes
Integrated MCU withADC
The Total Volatile Organic Compound (TVOC) output range is from 0ppb to 1187ppb.
10-bit measurement resolution
6-pin Pmod connector with I²C interface
Pass-through Pmod host port for daisy chaining

The Pmod AQS is designed to digitally report the Volatile Organic Compounds (VOCs) upon request by the host board.
Up to 10-bits of resolution collected by allowing for longer conversion times. Micro-hotplate technology which enables a
highly reliable solution for gas sensors, very fast cycle times and a significant reduction in average power consumption.

The Pmod AQS communicates with the host board via theI²C protocol. By first sending the 7-bit I²C address of 1011011
(0x5B) and then a read/write bit (high/low logic level, respectively), followed by the register address of interest at a
maximum clock frequency of 400kHz, users can both configure and read from the Pmod AQS.Header J2on the Pmod
AQS passes through all of the signals present on the mainHeader J1to allow for the daisy chaining of multiple I²C
compatible modules.

Application registers for the Pmod AQS

Parameter Min Typical Max

Power Supply Voltage 1.8 3.3

Serial Clock Frequency 10 100 400

Parameter Value

eCO2 output range 400-8192

TVOC output range 0-1187

Sleep Mode Current Draw at 1.8V 19

Features

Functional Description

Specifications

Interfacing with the Pmod

Application Register Map

Here is the series of commands to acquire relative humidity and temperature data from the Pmod AQs in pseudo I²C code.

1. Power on the Pmod AQS and wait at least 15 ms.

2. Call the device ID with a write bit

I2CBegin(0x5B); //device ID 0x81 with a write (0) bit

3. Wait to receive an ACK from the Slave Device

4. Write the device address that you want to talk to

I2CWrite(0x01); //address 0x01 corresponds to the Meas_mode

5. Wait to receive an ACK from the Slave Device

6. Delay at least 12.85 ms (6.35 ms for the Temperature Sensor and 6.50 ms for the Humidity Sensor)

Quick data acquisition

7. Read 4 bytes from the temperature and humidity registers (two 8 byte samples from each, MSB then LSB)

8. Read up to 8 bytes from the Alg_result_data register (two 8 byte samples MSB then LSB for eCO2 and two 8 byte
samples MSB then LSB for VOC)

The PmodAQS Jumper setting when using the Demo's are JP1:WAKE Enabled, JP2:Both Enabled, JP3:Enabled.

The Pmod AQS is an ideal Pmod to use in long term Air quality application. As a very low power Pmod between
measurements, long term data to measure VOC changes in an environment can easily be collected.

Any external power applied to the Pmod AQS must be within 1.8 V and 3.3 V to ensure that the on-board chips operate
correctly; however, it is recommended that Pmod is operated at 3.3 V.

A sample diagram for writing to and reading from the Pmod AQS taken from the CCS811 datasheet are provided below:

Example writing to the Pmod AQS

I2CReadMultiple(4); //read four bytes, sending an ACK to the slave after each byte received

I2CReadMultiple(8)); //read up to 8 bytes, sending an ACK to the slave after each byte rece

Header J1 Header J2 Jumper Blocks

Pin Signal Description Pin Signal Description Jumper State Desc

1 IO/INT IO or

Interrupt

1 IO/INT IO or

INterrupt

JP1 Enable

Left

Set to RST

2 WAKE/RST WAKE or

RESET

2 WAKE/RST WAKE or

RESET

JP1 Enable

Right

Set to WA

3 SCL Serial Clock 3 SCL Serial Clock JP2 Both

Enabled

2.2 kΩ re
enabled o
and SCL l

4 SDA Serial Data 4 SDA Serial Data JP2 Both

Disabled

2.2 kΩ re
disabled o
and SCL l

5 GND Power Supply

Ground

5 GND Power

Supply
Ground

JP3 Enabled IO/INTe

6 VCC Power Supply

(1.8V/3.3V)

6 VCC Power

Supply
(1.8V/3.3V)

Pinout Table Diagram

Timing Diagram

Example reading from the Pmod AQS

The pins on the pin header are spaced 100 mil apart. The PCB is 1.25 inches long on the sides parallel to the pins on the
pin header and 0.8 inches long on the sides perpendicular to the pin header.

The schematics of the Pmod AQS are availablehere. Additional information about the VOCs Gas sensor including
communication modes and specific timings of the chip can be found in the datasheethere.

Example code and more specific information on how to use the Pmod AQS can be found on itsResource Center.

If you have any questions or comments about the Pmod AQS, feel free to post them under the appropriate section (“Add­on Boards”) of theDigilent Forum.

Physical Dimensions

Additional Information