Adjutant

Adjuant is the development firmware repository for the Scintilla air quality monitoring IoT device.

Hardware Overview

The Adjutant uses an ESP-12F microcontroller.

Power, Ground, and Reset circuits

Prototypical versions of the Adjutant utilize a physical button flashing system connected to RST and GPIO 0. So far there is no reason to put the MCU to sleep and no external method to control such actions, so the EN pin is permenantly tied to 3V3.

Pin Assignments:

• VCC: BU33SD5WG 3V3 voltage regulator
• GND: Ground
• RST: Reset circuit (RST switch, pulled HIGH)
• EN: (pulled HIGH)

I2C & Flash Circuit

GPIO 0 and GPIO 2 are both pulled HIGH in order to enable the ESP-12F. Both of these pins double as the SCL and SDA pins, respectively.

I2C communications should work out of the box, provided you assign the correct pins.

Pin Assignments:

• GPIO 0: SCL (FLSH switch, pulled HIGH)
• GPIO 2: SDA (pulled HIGH)

Example

#include <Wire.h>

#define SDA 2
#define SCL 0

setup()
{
    // Inititialize I2C bus with explicit pin declarations
    Wire.pins(SDA, SCL);
    Wire.begin();
}

UART Mux Circuit

The Adjutant uses a 74LV4052a IC to mux between three UART channels, allowing it to communicate with the SDS021 dust sensor and SKM61 GPS module.

Pin Assignments:

• TX: FTDI / SDS021 / SKM61
• RX: FTDI / SDS021 / SKM61
• GPIO 10: UART internal select
• GPIO 15: UART external select (pulled LOW)

If the external select pin (GPIO 15) is pulled LOW (default), the UART mux will only communicate with the FTDI chip and the internel select pin is ignored. If the external select pin is driven HIGH, the internel select pin (GPIO 10) can be driven LOW to communicate with the SDS021 dust sensor or HIGH to communicate with the SKM61 GPS module.

Control of the UART mux circuit is provided by UARTMux class which must be instantiated using the appropreate pin assignments and initialized using the Begin() method. Once the mux circuit is initialized, you can use the Select() method to switch between circuits identified in the UARTMux::ETarget enum.

Example:

#include <UARTMux.h>

#define USEL_INT 10
#define USEL_EXT 15

UARTMux uart = UARTMux(USEL_EXT, USEL_INT);

setup()
{
    uart.Begin();

    // Select dust sensor
    uart.Select(UARTMux::ETarget::SDS021);
    // ...

    // Select GPS module
    uart.Select(UARTMux::ETarget::SKM61);
    // ...

    // Select FTDI chip
    uart.Select(UARTMux::ETarget::FTDI);
    // ...
}

Warning: The UART mux is highly sensitive to timing issues and race conditions. The UARTMux library is designed to wait until the serial output buffer is cleared, but it is up to the developer to calculate an appropreate delay when waiting for a message to return from the dust sensor or GPS module.

PSTAT Circuit

The Adjutant is also armed with a full suite of SPEC gas sensors. Each of these sensors is controlled by an LMP91000 potentiostat IC, which can be programmed using the PSTAT class with the associated configurations found in the SPEC library.

The corresponding output voltage for the potentiostat circuit is measured using an MCP3425 IC, which can be configured using the ADC() method of the PSTAT class.

Pin Assignments:

• GPIO 14: PSTAT select 0
• GPIO 12: PSTAT select 1
• GPIO 13: PSTAT select 2
• GPIO 16: MENB (read/write to LMP91000)

Example:

#include <PSTAT.h>
#include <SPEC.h>

#define MENB 16
#define PSTAT_0 14
#define PSTAT_1 12
#define PSTAT_2 13

// Instantiate PSTAT circuit
PSTAT pstat = PSTAT(PSTAT_0, PSTAT_1, PSTAT_2, MENB);

setup()
{
    // Initialize PSTAT pins
    pstat.Begin();

    // Configure PSTAT ADC
    pstat.ADC(true, MCP3425::EResolution::d16Bit, MCP3425::EGain::x8);

    // Configure SPEC gas sensors
    pstat.Configure(0, SPEC::CO);
    pstat.Configure(1, SPEC::O3);
    pstat.Configure(2, SPEC::SO2);
    pstat.Configure(3, SPEC::NO2);
    pstat.Configure(4, SPEC::H2S);
}

loop()
{
    double v_out;
    for (int i = 0; i < 5; i++)
    {
        // Select the gas sensor and measure the output voltage
        pstat.Select(i);
        v_out = pstat.ADC();

        // Do something with the data
        // ...
    }
}

Unused Pins

• GPIO 5: (NC)

• GPIO 4: (NC)

• GPIO 9: (NC)

• ADC: (NC)

• SCLK: (NC)

• MOSI: (NC)

• MISO: (NC)

• CSO: (NC)

Cloning and Flashing

To clone all submodules:

$ git submodule init
$ git submodule update

To update all submodules:

$ git submodule foreach git pull origin master

To build on a vanilla Ubuntu installation:

$ sudo cpan YAML