The project was initiated by Jonathan Chiang (ADM-TW) and deligated to Maker's Club, aiming to deploy air quality sensors to Trend Micro's buildings to acquire real-time readings of,

• PM 2.5
• temperature
• humidity
• CO2 in ppm

We decided to use the following configuration,

• G3 PM 2.5 sensor (sold in Taobao, can be replaced by A4 or G5)
• SHT31 I2C sensor (precise temperature + humidity)
• SenseAir S8 (CO2)
• Nokia 5110 LCD as indicator and debugger
• Extra LED as a chasis indicator

We use Raspberry Pi Model B+. Don't use Model A as the GPIO pins are not enough for extended use.

G3 talks UART in 9600 N 8 1. Connect the pins as (left RPi, right G3):

• 5V to Pin 1 (VIN)
• GND to Pin 2 (GND)
• RX to Pin 5 (TX)

SHT31 works on I2C. Connect the pins as (left RPi, right LCD):

• 3V3 to VIN (can be 5V, but we used all 5V in our configuration)
• GND to GND
• SDA1 to SDA
• SCL to CLK

Copied from [https://learn.adafruit.com/nokia-5110-3310-lcd-python-library/usage](Adafruit Nokia 5110 Library), the pins are (left RPi, right LCD):

• 3.3V to VIN
• GND to GND
• GPIO23 to D/C
• GPIO24 to RST
• CE0 to CE
• SCLK to CLK
• MOSI to DIN

Use normal 3.3V LED without resistor. It's OK.

• GND to GND
• GPIO16 to VIN

S8 uses a weird type of ModBus. We used up onboard UART, so we have to use software serial. It's 9600 N 8 1.

• 5V to G+ (upper)
• GND to G0 (lower)
• GPIO20 (soft RX) to TX (lower)
• GPIO21 (soft TX) to RX (upper)

To make it easy to assemble, please check the following pin-out.

SHT31_VIN          3V3  1 | 2  5V         S8_G+
SHT31_SDA      SDA I2C  3 | 4  5V         G3_VIN
SHT31_CLK      SCL I2C  5 | 6  GND        G3_GND
                 GPIO4  7 | 8  UART_TX
SHT31_GND          GND  9 | 10 UART_RX    G3_TX
                GPIO17 11 | 12 PCM_CLK
                GPIO27 13 | 14 GND        5110_GND
                GPIO22 15 | 16 GPIO23     5110_DC
5110_VIN           3V3 17 | 18 GPIO24     5110_RST
5110_DIN          MOSI 19 | 20 GND
                  MISO 21 | 22 GPIO25
5110_CLK       SPI_CLK 23 | 24 SPI_CE0    5110_CE
                   GND 25 | 26 SPI_CE1
                 ID_SD 27 | 28 ID_SC
                 GPIO5 29 | 30 GND        S8_G0
                 GPIO6 31 | 32 GPIO12
                GPIO13 33 | 34 GND        IND_LED_GND
                GPIO19 35 | 36 GPIO16     IND_LED_VIN
SHUTDOWN_SW     GPIO26 37 | 38 GPIO20     S8_TX
SHUTDOWN_SW        GND 39 | 40 GPIO21     S8_RX

External shutdown switch are defined to GPIO26. Ground it to gracefully shutdown.

We have 10 GPIO left for further use.

It is necessary to enable I2C, SPI and GPIO support in Raspbian. You should enable Serial, but there is something to patch.

1. Comment out T0:23:respawn:/sbin/getty -L ttyAMA0 in /etc/inittab.
2. Remove console=ttyAMA0,115200 in /boot/cmdline.txt.
3. Serial console is thus disabled. Use HDMI.
4. Add i2c-dev to /etc/modules.
5. Install pigpio from joan2937 for software serial, and run /usr/local/bin/pigpiod when system boots.
6. Install software, run ./install.sh

sudo apt-get install python-pip python-dev build-essential python-imaging git python-smbus i2c-tools supervisord
sudo pip install RPi.GPIO requests
cd ~/
git clone https://github.com/adafruit/Adafruit_Nokia_LCD.git
cd Adafruit_Nokia_LCD
sudo python setup.py install
echo 'i2c-dev' | sudo tee -a /etc/modules
cd ~/
git clone https://github.com/joan2937/pigpio
cd pigpio
make
sudo make install

Indicator LED uses RPi.GPIO, while software serial uses pigpio. We use different package to prevent possible dysfunction of one or the other.

Better enable unattended update and disable PasswordAuthentication in /etc/ssh/sshd_config.

Raspberry Pi posts the readings every 10 seconds to a C&C server. The server locates at http://10.1.148.5 (temporarily). After POST, the server sends commands like "Indicator LED ON" or "Location is A19F Left". Any more serious operation (like to change C&C IP) shall be done with ssh -c.

Setup SQLite3 database with sqlite3 airmon.sq3 < schema.sql.

• Use pre-shared SSH key.
• Client IP and Mac shall be obtained by POST.