MH-Z19B

// MH-Z19B on Arduino Uno: wiring and a free simulation at https://www.tinkered.ai/components/mh-z19b
// MH-Z19B on an Arduino Uno: Vin 5V, sensor Tx to D2, sensor Rx to D3, 9600 baud
#include <SoftwareSerial.h>
#include <MHZ19.h>

SoftwareSerial co2Serial(2, 3);  // RX (from sensor Tx), TX (to sensor Rx)

MHZ19 co2;
unsigned long warmupEnd;

void setup() {
  Serial.begin(115200);
  co2Serial.begin(9600);
  co2.begin(co2Serial);
  // Automatic baseline calibration (ABC) is on from the factory; leave it on if the
  // sensor sees fresh outdoor air (about 400 ppm) regularly, else call co2.autoCalibration(false).
  warmupEnd = millis() + 180000UL;  // 3 minute preheat
  Serial.println("MH-Z19B started, warming up for 3 minutes");
}

void loop() {
  int ppm = co2.getCO2();
  if (co2.errorCode != RESULT_OK) {
    Serial.print("No valid reply, error code ");
    Serial.println(co2.errorCode);
  } else {
    Serial.print("CO2: ");
    Serial.print(ppm);
    Serial.print(" ppm   Sensor temperature: ");
    Serial.print(co2.getTemperature(), 0);
    Serial.print(" C");
    if ((long)(millis() - warmupEnd) < 0) Serial.print("   (still warming up)");
    Serial.println();
  }
  delay(5000);
}

// MH-Z19B on ESP32 DevKit V1: wiring and a free simulation at https://www.tinkered.ai/components/mh-z19b
// MH-Z19B on an ESP32 DevKit V1: Vin VIN (5 V), sensor Tx to GPIO16, sensor Rx to GPIO17, 9600 baud
#include <MHZ19.h>

MHZ19 co2;
unsigned long warmupEnd;

void setup() {
  Serial.begin(115200);
  Serial2.begin(9600, SERIAL_8N1, 16, 17);  // RX2, TX2
  co2.begin(Serial2);
  // Automatic baseline calibration (ABC) is on from the factory; leave it on if the
  // sensor sees fresh outdoor air (about 400 ppm) regularly, else call co2.autoCalibration(false).
  warmupEnd = millis() + 180000UL;  // 3 minute preheat
  Serial.println("MH-Z19B started, warming up for 3 minutes");
}

void loop() {
  int ppm = co2.getCO2();
  if (co2.errorCode != RESULT_OK) {
    Serial.print("No valid reply, error code ");
    Serial.println(co2.errorCode);
  } else {
    Serial.print("CO2: ");
    Serial.print(ppm);
    Serial.print(" ppm   Sensor temperature: ");
    Serial.print(co2.getTemperature(), 0);
    Serial.print(" C");
    if ((long)(millis() - warmupEnd) < 0) Serial.print("   (still warming up)");
    Serial.println();
  }
  delay(5000);
}

// MH-Z19B on Raspberry Pi Pico: wiring and a free simulation at https://www.tinkered.ai/components/mh-z19b
// MH-Z19B on a Raspberry Pi Pico (arduino-pico): Vin VBUS, sensor Tx to GP1, sensor Rx to GP0, 9600 baud
#include <MHZ19.h>

MHZ19 co2;
unsigned long warmupEnd;

void setup() {
  Serial.begin(115200);
  Serial1.setRX(1);
  Serial1.setTX(0);
  Serial1.begin(9600);
  co2.begin(Serial1);
  // Automatic baseline calibration (ABC) is on from the factory; leave it on if the
  // sensor sees fresh outdoor air (about 400 ppm) regularly, else call co2.autoCalibration(false).
  warmupEnd = millis() + 180000UL;  // 3 minute preheat
  Serial.println("MH-Z19B started, warming up for 3 minutes");
}

void loop() {
  int ppm = co2.getCO2();
  if (co2.errorCode != RESULT_OK) {
    Serial.print("No valid reply, error code ");
    Serial.println(co2.errorCode);
  } else {
    Serial.print("CO2: ");
    Serial.print(ppm);
    Serial.print(" ppm   Sensor temperature: ");
    Serial.print(co2.getTemperature(), 0);
    Serial.print(" C");
    if ((long)(millis() - warmupEnd) < 0) Serial.print("   (still warming up)");
    Serial.println();
  }
  delay(5000);
}