Initial commit

.gitignore

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+.pio
+.idea
+.vscode
+CMakeLists.txt
+CMakeListsPrivate.txt
+cmake-build-az-delivery-devkit-v4
+cmake-build-debug
+

README.md

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+# esp32-co2-mhz19b
+This project displays the current co2 levels, along with temperature and humidity information, on a HD44780 16x2 display. All of this is powered by an ESP32 devkit, a AHT10 temperature and humidity sensor, and a MH-Z19B NDIR CO2 sensor.
+
+## Wiring
+![Wiring diagram](img/wiring.jpeg)
+
+The main components here are wired up like this:
+- The green, yellow and red LEDs are connected to ground and pins 25, 33 and 32 respectively
+- The HD44780 16x2 display is connected to an I2C daughterboard, which itself is connected to +5V, ground, as well as the I2C bus pins of the ESP32, 22 for clock and 21 for data
+- The AHT10 temperature and humidity sensor is connected to +3.3V, ground, and the I2C bus (see above)
+- The MH-Z19B NDIR CO2 sensor is connected to +5V and ground for the 4 pin cluster, and to pins 16 and 17 (ESP32 HardwareSerial2; MH-Z19B side pins Tx and Rx respectively)
+- A button to toggle the backlight is connected between pin 23 and ground

include/README

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+
+This directory is intended for project header files.
+
+A header file is a file containing C declarations and macro definitions
+to be shared between several project source files. You request the use of a
+header file in your project source file (C, C++, etc) located in `src` folder
+by including it, with the C preprocessing directive `#include'.
+
+```src/main.c
+
+#include "header.h"
+
+int main (void)
+{
+ ...
+}
+```
+
+Including a header file produces the same results as copying the header file
+into each source file that needs it. Such copying would be time-consuming
+and error-prone. With a header file, the related declarations appear
+in only one place. If they need to be changed, they can be changed in one
+place, and programs that include the header file will automatically use the
+new version when next recompiled. The header file eliminates the labor of
+finding and changing all the copies as well as the risk that a failure to
+find one copy will result in inconsistencies within a program.
+
+In C, the usual convention is to give header files names that end with `.h'.
+It is most portable to use only letters, digits, dashes, and underscores in
+header file names, and at most one dot.
+
+Read more about using header files in official GCC documentation:
+
+* Include Syntax
+* Include Operation
+* Once-Only Headers
+* Computed Includes
+
+https://gcc.gnu.org/onlinedocs/cpp/Header-Files.html

lib/README

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+
+This directory is intended for project specific (private) libraries.
+PlatformIO will compile them to static libraries and link into executable file.
+
+The source code of each library should be placed in a an own separate directory
+("lib/your_library_name/[here are source files]").
+
+For example, see a structure of the following two libraries `Foo` and `Bar`:
+
+|--lib
+|  |
+|  |--Bar
+|  |  |--docs
+|  |  |--examples
+|  |  |--src
+|  |     |- Bar.c
+|  |     |- Bar.h
+|  |  |- library.json (optional, custom build options, etc) https://docs.platformio.org/page/librarymanager/config.html
+|  |
+|  |--Foo
+|  |  |- Foo.c
+|  |  |- Foo.h
+|  |
+|  |- README --> THIS FILE
+|
+|- platformio.ini
+|--src
+   |- main.c
+
+and a contents of `src/main.c`:
+```
+#include <Foo.h>
+#include <Bar.h>
+
+int main (void)
+{
+  ...
+}
+
+```
+
+PlatformIO Library Dependency Finder will find automatically dependent
+libraries scanning project source files.
+
+More information about PlatformIO Library Dependency Finder
+- https://docs.platformio.org/page/librarymanager/ldf.html

platformio.ini

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+; PlatformIO Project Configuration File
+;
+;   Build options: build flags, source filter
+;   Upload options: custom upload port, speed and extra flags
+;   Library options: dependencies, extra library storages
+;   Advanced options: extra scripting
+;
+; Please visit documentation for the other options and examples
+; https://docs.platformio.org/page/projectconf.html
+
+[env:az-delivery-devkit-v4]
+platform = espressif32
+board = az-delivery-devkit-v4
+framework = arduino
+upload_protocol = esptool
+lib_deps = 
+	wifwaf/MH-Z19@^1.5.3
+	adafruit/Adafruit AHTX0@^2.0.1
+	fmalpartida/LiquidCrystal@^1.5.0

src/main.cpp

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+#include <Arduino.h>
+#include "MHZ19.h"
+#include "Adafruit_AHTX0.h"
+#include "LiquidCrystal_I2C.h"
+
+#define RX_PIN 16                                          // Rx pin which the MHZ19 Tx pin is attached to
+#define TX_PIN 17                                          // Tx pin which the MHZ19 Rx pin is attached to
+#define BAUDRATE 9600                                      // Device to MH-Z19 Serial baudrate (should not be changed)
+
+MHZ19 myMHZ19;                                             // Constructor for library
+Adafruit_AHTX0 aht;
+LiquidCrystal_I2C LCD(0x27,2,1,0,4,5,6,7,3,POSITIVE);
+
+int greenpin = 25;
+int yellownpin = 33;
+int redpin = 32;
+
+int backlightState = HIGH;
+int backlightUpdate = 0;
+
+int update_ival = 0;
+int override = 0;
+
+int cal_time = 5; //minutes
+
+void led(int red, int green, int yellow)
+{
+    analogWrite(redpin, red);
+    analogWrite(greenpin, green);
+    analogWrite(yellownpin, yellow);
+}
+
+void IRAM_ATTR BacklightToggle() {
+    backlightUpdate = true;
+}
+
+void setup()
+{
+    Serial.begin(9600);                                     // Device to serial monitor feedback
+
+    Serial2.begin(BAUDRATE, SERIAL_8N1, RX_PIN, TX_PIN);                               // (Uno example) device to MH-Z19 serial start
+    myMHZ19.begin(Serial2);                                // *Serial(Stream) refence must be passed to library begin().
+
+    myMHZ19.autoCalibration();                              // Turn auto calibration ON (OFF autoCalibration(false))
+    myMHZ19.setRange(2000);
+
+    Serial.println("MHZ19 init:");
+    char myVersion[4];
+    myMHZ19.getVersion(myVersion);
+    Serial.print("\nFirmware Version: ");
+    for(byte i = 0; i < 4; i++)
+    {
+        Serial.print(myVersion[i]);
+        if(i == 1)
+            Serial.print(".");
+    }
+    Serial.println("");
+
+    Serial.print("Range: ");
+    Serial.println(myMHZ19.getRange());
+    Serial.print("Background CO2: ");
+    Serial.println(myMHZ19.getBackgroundCO2());
+    Serial.print("Temperature Cal: ");
+    Serial.println(myMHZ19.getTempAdjustment());
+    Serial.print("ABC Status: "); myMHZ19.getABC() ? Serial.println("ON") :  Serial.println("OFF");
+
+    if (!aht.begin()) {
+        Serial.println("Could not find AHT? Check wiring");
+        while (true);
+    }
+
+    LCD.begin(16, 2);
+    LCD.clear();
+    LCD.setBacklight(backlightState);
+    pinMode(23, INPUT_PULLUP);
+    attachInterrupt(23, BacklightToggle, FALLING);
+}
+
+void loop() {
+    if (backlightUpdate) {
+        backlightState = !backlightState;
+        backlightUpdate = false;
+        Serial.printf("Setting backlight to %i \n", backlightState);
+        LCD.setBacklight(backlightState);
+    }
+
+    if (update_ival-- > 0) {
+        delay(1000);
+        return;
+    }
+
+    update_ival = 5; //5sec
+
+    sensors_event_t humidity, temp;
+    aht.getEvent(&humidity, &temp);
+    LCD.setCursor(0, 0);
+    LCD.print(temp.temperature, 1);
+    LCD.print(" C   ");
+    LCD.setCursor(9, 0);
+    LCD.print(humidity.relative_humidity, 1);
+    LCD.print("%rH");
+
+    if (millis() >= (cal_time * 60000) && !override) {
+        LCD.setCursor(0, 1);
+        LCD.print("          Ready.");
+        override = true;
+    }
+
+    int co2 = myMHZ19.getCO2(false);
+    if (myMHZ19.errorCode != RESULT_OK) {
+        Serial.print("Error. Response Code: ");
+        Serial.println(myMHZ19.errorCode);          // Get the Error Code value
+        return;
+    }
+    LCD.setCursor(0, 1);
+    LCD.print(co2);
+    LCD.print("ppm   ");
+
+    if (co2 < 1000)
+        led(0, 1, 0);
+    else if (co2 < 1500)
+        led(0, 0, 5);
+    else
+        led(5, 0, 0);
+
+    if (millis() < (cal_time * 60000)) {
+        {
+            LCD.setCursor(8, 1);
+            LCD.printf("Cal..%2lum", ((cal_time * 60000) - millis()) / 60000);
+        }
+    }
+}

test/README

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+
+This directory is intended for PlatformIO Unit Testing and project tests.
+
+Unit Testing is a software testing method by which individual units of
+source code, sets of one or more MCU program modules together with associated
+control data, usage procedures, and operating procedures, are tested to
+determine whether they are fit for use. Unit testing finds problems early
+in the development cycle.
+
+More information about PlatformIO Unit Testing:
+- https://docs.platformio.org/page/plus/unit-testing.html