tested this library with a MH-Z14A module.

comment about how to change from MZ-H19B to MH-Z14A module is missing.

delays hided away in a library are bad coding practice!!

To the author: If your library is even available through the arduino-library-manager you should add INTENSIVE DOCUMENTAION

and having done a lot of tests including all kinds of extraordinary circumstances to make your library HIGH-reliable

GRRRR!!!!

It did not work reliable. After a few answers no more responds from the module shown in the serial monitor

So I used this code for testing (pre-heating and calibrating are disabled through commenting out

Anyway this code is aber to display the answer of the module on eah request

I uploaded this code new to my ESP8266 nodeMCU for re-checking if the code is working directly before copy & pasting this code here. So there is a high chance that this code will work `/*** Sample sketch for using a mh-z14a co2 with a ESP8266 for TESTING a MH_Z14A-sensor

Written by Erik Lemcke, combined out of the following samples:

https://www.letscontrolit.com/forum/viewtopic.php?f=2&t=1785&start=40, calibration sample by s3030150 https://www.home-assistant.io/blog/2015/10/11/measure-temperature-with-esp8266-and-report-to-mqtt/, home assistant mqqt by Paulus Schoutsen

modified by Stefan Ludwig (StefanL38) wiring: nodeMCU mh-z14a D7(GPIO13)--> Rx D6(GPIO12)<-- Tx GND GND

use the nodeMCU-Vin pin to supply with 5V, the mh-z14a needs 5v ***/

include

define INTERVAL 5000

//Tx_pin of MH_Z is connected to nodeMCU-RX-pin D6 (GPIO12)

define nodeMCU_D6_GPIO12 12

define MH_Z14_TX nodeMCU_D6_GPIO12

//Rx_pin of MH_Z is connected to nodeMCU-TX-pin D7 (GPIO13)

define nodeMCU_D7_GPIO13 13

define MH_Z14_R_Pin nodeMCU_D7_GPIO13

byte mhzResp[9]; // 9 bytes bytes response byte mhzCmdReadPPM[9] = {0xFF,0x01,0x86,0x00,0x00,0x00,0x00,0x00,0x79}; byte mhzCmdCalibrateZero[9] = {0xFF,0x01,0x87,0x00,0x00,0x00,0x00,0x00,0x78}; byte mhzCmdABCEnable[9] = {0xFF,0x01,0x79,0xA0,0x00,0x00,0x00,0x00,0xE6}; byte mhzCmdABCDisable[9] = {0xFF,0x01,0x79,0x00,0x00,0x00,0x00,0x00,0x86}; byte mhzCmdReset[9] = {0xFF,0x01,0x8d,0x00,0x00,0x00,0x00,0x00,0x72}; byte mhzCmdMeasurementRange1000[9] = {0xFF,0x01,0x99,0x00,0x00,0x00,0x03,0xE8,0x7B}; byte mhzCmdMeasurementRange2000[9] = {0xFF,0x01,0x99,0x00,0x00,0x00,0x07,0xD0,0x8F}; byte mhzCmdMeasurementRange3000[9] = {0xFF,0x01,0x99,0x00,0x00,0x00,0x0B,0xB8,0xA3}; byte mhzCmdMeasurementRange5000[9] = {0xFF,0x01,0x99,0x00,0x00,0x00,0x13,0x88,0xCB};

int shifts = 0 ; int co2ppm;

long previousMillis = 0;

// the softwareserial interface is defined from the view of the nodeMCU // nodeMCUs Rx is MH_Zs Tx and vice versa nodeMCUs Tx is MH_Zs Rx

//basic definition of Software-serial is SoftwareSerial MySerial(Rx,Tx)

// from the nodeMCUs view using nodeMCU-pins SoftwareSerial co2Serial(nodeMCU_D6_GPIO12, nodeMCU_D7_GPIO13); // define MH-Z14A

// from the MH_Zs view using the MH_Z-pins //SoftwareSerial co2Serial(MH_Z14_TX, MH_Z14_R_Pin); // define MH-Z14A

byte checksum(byte response[9]){ byte crc = 0; for (int i = 1; i < 8; i++) { crc += response[i]; } crc = 255 - crc + 1; return crc; }

void disableABC() { co2Serial.write(mhzCmdABCDisable, 9); }

void enableABC() { co2Serial.write(mhzCmdABCEnable, 9); }

void setRange5000() { co2Serial.write(mhzCmdMeasurementRange5000, 9); }

void calibrateZero(){ co2Serial.write(mhzCmdCalibrateZero, 9); }

int readCO2() { byte cmd[9] = {0xFF, 0x01, 0x86, 0x00, 0x00, 0x00, 0x00, 0x00, 0x79}; byte response[9]; co2Serial.write(cmd, 9); // The serial stream can get out of sync. The response starts with 0xff, try to resync. while (co2Serial.available() > 0 && (unsigned char)co2Serial.peek() != 0xFF) { co2Serial.read(); yield(); shifts++; }

memset(response, 0, 9); co2Serial.readBytes(response, 9);

for (int i = 0; i < 9; i++) { Serial.print(" 0x"); Serial.print(response[i], HEX); } Serial.println(" Response OK. Shifts=" + String(shifts));

if (response[1] != 0x86) { Serial.println(" Invalid response from co2 sensor!"); delay(1000); return -1; }

if (response[8] == checksum(response)) { int responseHigh = (int) response[2]; int responseLow = (int) response[3]; int ppm = (256 * responseHigh) + responseLow; return ppm; } else { Serial.println("CRC error!"); return -1; } }

void setup() {

Serial.begin(115200); Serial.println("Startup"); co2Serial.begin(9600); Serial.println("co2Serial.begin(9600);");

unsigned long previousMillis = millis(); delay(500); / Serial.println("Disabling ABC"); disableABC(); / Serial.println("Setting range to 5000"); setRange5000(); /
Serial.println("Waiting half an hour before calibrating zero"); delay(1800000); calibrateZero(); Serial.println("Zero was calibrated"); /
Serial.println("leaving Setup");

}

long lastMsg = 0;

void loop() { unsigned long now = millis(); //send a meaage every minute if (now - lastMsg > 5 * 1000) { lastMsg = now; unsigned long currentMillis = millis(); if (abs(currentMillis - previousMillis) > INTERVAL) { previousMillis = currentMillis; Serial.print("Requesting CO2 concentration..."); co2ppm = -999; co2ppm = readCO2();

  //If no proper co2 value is returned, try again
  while (co2ppm == -1){
    yield();
    Serial.print("re-Requesting CO2 concentration...");
    co2ppm = readCO2();  
  }

  Serial.println("  PPM = " + String(co2ppm));
}

} }`

tobiasschuerg / MH-Z-CO2-Sensors

Documentation about how to change from MH-Z19B to MH-Z14A module is missing #21

include

include

include

define INTERVAL 5000

define nodeMCU_D6_GPIO12 12

define MH_Z14_TX nodeMCU_D6_GPIO12

define nodeMCU_D7_GPIO13 13

define MH_Z14_R_Pin nodeMCU_D7_GPIO13