RFM9X.IoTCore Adafruit LoRa Radio Bonnet support

The RFM9X chip select line on the Adafruit LoRa Radio Bonnet 868 or 915MHz with OLED RFM95W is connected to pin 26(CS1), the reset line to pin 22(GPIO25) and the interrupt line to pin 15(GPIO22).

When I ran the RFM9XLoRaDeviceClient from my RFM9X.IoTCore library with the following configuration

#if ADAFRUIT_RADIO_BONNET
	private const byte ResetLine = 25;
	private const byte InterruptLine = 22;
	private Rfm9XDevice rfm9XDevice = new Rfm9XDevice(ChipSelectPin.CS1, ResetLine, InterruptLine);
#endif

public void Run(IBackgroundTaskInstance taskInstance)
{
	rfm9XDevice.Initialise(Frequency, paBoost: true, rxPayloadCrcOn : true);
#if DEBUG
	rfm9XDevice.RegisterDump();
#endif
	rfm9XDevice.OnReceive += Rfm9XDevice_OnReceive;
#if ADDRESSED_MESSAGES_PAYLOAD
	rfm9XDevice.Receive(UTF8Encoding.UTF8.GetBytes(Environment.MachineName));
#else
	rfm9XDevice.Receive();
#endif
	rfm9XDevice.OnTransmit += Rfm9XDevice_OnTransmit;

	Task.Delay(10000).Wait();

	while (true)
	{
		string messageText = string.Format("Hello from {0} ! {1}", Environment.MachineName, MessageCount);
		MessageCount -= 1;

		byte[] messageBytes = UTF8Encoding.UTF8.GetBytes(messageText);
		Debug.WriteLine("{0:HH:mm:ss}-TX {1} byte message {2}", DateTime.Now, messageBytes.Length, messageText);
#if ADDRESSED_MESSAGES_PAYLOAD
		this.rfm9XDevice.Send(UTF8Encoding.UTF8.GetBytes("AddressHere"), messageBytes);
#else
		this.rfm9XDevice.Send(messageBytes);
#endif
		Task.Delay(10000).Wait();
	}
}
#endif

I could see messages being sent and received in the debug output

Register 0x3e - Value 0X00 - Bits 00000000
Register 0x3f - Value 0X00 - Bits 00000000
Register 0x40 - Value 0X00 - Bits 00000000
Register 0x41 - Value 0X00 - Bits 00000000
Register 0x42 - Value 0X12 - Bits 00010010
...
The thread 0xec4 has exited with code 0 (0x0).
The thread 0x868 has exited with code 0 (0x0).
22:21:47-RX PacketSnr 9.8 Packet RSSI -80dBm RSSI -122dBm = 59 byte message "�LoRaIoT1Maduino2at 62.8,ah 77,wsa 1,wsg 3,wd 34.88,r 0.00,"
22:21:52-TX 31 byte message Hello from AdaFruitIOLoRa ! 255
22:21:52-TX Done
The thread 0xbf8 has exited with code 0 (0x0).
The program '[3380] backgroundTaskHost.exe' has exited with code -1 (0xffffffff).

Adafruit LoRa Radio Bonnet with OLED – RadioFruit

Today a package arrived from Adafruit which contained an Adafruit LoRa Radio Bonnet 868 or 915MHz with OLED RFM95W.

The shield has a small OLED screen and 3 buttons connected to General Purpose Input Output(GPIO) pins.

The first step was to check the pin assignments of the 3 buttons.

/*
    Copyright ® 2019 Feb devMobile Software, All Rights Reserved
 
    MIT License

    Permission is hereby granted, free of charge, to any person obtaining a copy
    of this software and associated documentation files (the "Software"), to deal
    in the Software without restriction, including without limitation the rights
    to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
    copies of the Software, and to permit persons to whom the Software is
    furnished to do so, subject to the following conditions:

    The above copyright notice and this permission notice shall be included in all
    copies or substantial portions of the Software.

    THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
    IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
    FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
    AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
    LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
    OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
    SOFTWARE

	 Adafruit documentation page
	 https://learn.adafruit.com/adafruit-radio-bonnets/pinouts

    Button 1: GPIO 5 
    Button 2: GPIO 6
    Button 3: GPIO 12 

 */
namespace devMobile.IoT.Rfm9x.AdafruitButtons
{
	using System;
	using System.Diagnostics;
	using Windows.ApplicationModel.Background;
	using Windows.Devices.Gpio;

	public sealed class StartupTask : IBackgroundTask
    {
		private BackgroundTaskDeferral backgroundTaskDeferral = null;
		private GpioPin InterruptGpioPin1 = null;
		private GpioPin InterruptGpioPin2 = null;
		private GpioPin InterruptGpioPin3 = null;
		private const int InterruptPinNumber1 = 5;
		private const int InterruptPinNumber2 = 6;
		private const int InterruptPinNumber3 = 12;
		private readonly TimeSpan debounceTimeout = new TimeSpan(0, 0, 15);


		public void Run(IBackgroundTaskInstance taskInstance)
        {
			Debug.WriteLine("Application startup");

			try
			{
				GpioController gpioController = GpioController.GetDefault();

				InterruptGpioPin1 = gpioController.OpenPin(InterruptPinNumber1);
				InterruptGpioPin1.SetDriveMode(GpioPinDriveMode.InputPullUp);
				InterruptGpioPin1.ValueChanged += InterruptGpioPin_ValueChanged; ;

				InterruptGpioPin2 = gpioController.OpenPin(InterruptPinNumber2);
				InterruptGpioPin2.SetDriveMode(GpioPinDriveMode.InputPullUp);
				InterruptGpioPin2.ValueChanged += InterruptGpioPin_ValueChanged; ;

				InterruptGpioPin3 = gpioController.OpenPin(InterruptPinNumber3);
				InterruptGpioPin3.SetDriveMode(GpioPinDriveMode.InputPullUp);
				InterruptGpioPin3.ValueChanged += InterruptGpioPin_ValueChanged; ;

				Debug.WriteLine("Digital Input Interrupt configuration success");
			}
			catch (Exception ex)
			{
				Debug.WriteLine($"Digital Input Interrupt configuration failed " + ex.Message);
				return;
			}

			//enable task to continue running in background
			backgroundTaskDeferral = taskInstance.GetDeferral();
		}

		private void InterruptGpioPin_ValueChanged(GpioPin sender, GpioPinValueChangedEventArgs args)
		{
			Debug.WriteLine($"Digital Input Interrupt {sender.PinNumber} triggered {args.Edge}");
		}
	}
}

When I ran the application it produced the following output when I pressed the three buttons (left->right) which confirmed I had the correct GPIO pins configuration.

Application startup
'backgroundTaskHost.exe' (CoreCLR: CoreCLR_UWP_Domain): Loaded 'C:\Data\Programs\WindowsApps\Microsoft.NET.CoreFramework.Debug.2.2_2.2.27129.1_arm__8wekyb3d8bbwe\System.Runtime.WindowsRuntime.dll'. Skipped loading symbols. Module is optimized and the debugger option 'Just My Code' is enabled.
Digital Input Interrupt configuration success
Digital Input Interrupt 5 triggered FallingEdge
Digital Input Interrupt 5 triggered RisingEdge
Digital Input Interrupt 6 triggered FallingEdge
Digital Input Interrupt 6 triggered RisingEdge
Digital Input Interrupt 12 triggered FallingEdge
Digital Input Interrupt 12 triggered RisingEdge

The next step was to get the Serial Peripheral Interface (SPI) interface for the module working.

/*
    Copyright ® 2019 Feb devMobile Software, All Rights Reserved
 
    MIT License

    Permission is hereby granted, free of charge, to any person obtaining a copy
    of this software and associated documentation files (the "Software"), to deal
    in the Software without restriction, including without limitation the rights
    to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
    copies of the Software, and to permit persons to whom the Software is
    furnished to do so, subject to the following conditions:

    The above copyright notice and this permission notice shall be included in all
    copies or substantial portions of the Software.

    THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
    IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
    FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
    AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
    LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
    OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
    SOFTWARE

	 Adafruit documentation page
	 https://learn.adafruit.com/adafruit-radio-bonnets/pinouts

	 CS : CE1
	 RST : GPIO25
	 IRQ : GPIO22 (DIO0)
	 Unused : GPIO23 (DIO1)
	 Unused : GPIO24 (DIO2)
 */
namespace devMobile.IoT.Rfm9x.AdafruitSPI
{
	using System;
	using System.Diagnostics;
	using System.Threading;
	using Windows.ApplicationModel.Background;
	using Windows.Devices.Spi;

	public sealed class StartupTask : IBackgroundTask
	{
		public void Run(IBackgroundTaskInstance taskInstance)
		{
			SpiController spiController = SpiController.GetDefaultAsync().AsTask().GetAwaiter().GetResult();
			var settings = new SpiConnectionSettings(1)
			{
				ClockFrequency = 500000,
				Mode = SpiMode.Mode0,   // From SemTech docs pg 80 CPOL=0, CPHA=0
			};

			SpiDevice Device = spiController.GetDevice(settings);

			while (true)
			{
				byte[] writeBuffer = new byte[] { 0x42 }; // RegVersion
				byte[] readBuffer = new byte[1];

				Device.TransferSequential(writeBuffer, readBuffer);

				byte registerValue = readBuffer[0];
				Debug.WriteLine("Register 0x{0:x2} - Value 0X{1:x2} - Bits {2}", 0x42, registerValue, Convert.ToString(registerValue, 2).PadLeft(8, '0'));

				Thread.Sleep(10000);
			}
		}
	}
}

The output confirm the code worked

'backgroundTaskHost.exe' (CoreCLR: CoreCLR_UWP_Domain): Loaded 'C:\Data\Programs\WindowsApps\Microsoft.NET.CoreFramework.Debug.2.2_2.2.27129.1_arm__8wekyb3d8bbwe\System.Threading.Thread.dll'. Skipped loading symbols. Module is optimized and the debugger option 'Just My Code' is enabled.
Register 0x42 - Value 0X12 - Bits 00010010
Register 0x42 - Value 0X12 - Bits 00010010

The next step is to build support for this shield into my RFM9X.IoTCore library and get the OLED working.

Windows 10 IoT Core Field Gateways “less is more”

After looking back at the technical support interactions for my Azure IoT Hubs Windows 10 IoT Core Field Gateway & AdaFruit.IO LoRa Windows 10 IoT Core Field Gateway I think removing a “feature” might make it easier for first time users.

In an early version of the software I used to provide a sample configuration JSON file in the associated GitHub repository. Users had to download this file to a computer, update it with their Azure IOT Hub or Azure IoT Central connection string or AdafruitIO APIKey , frequency and device address, then upload to the field gateway.

In a later version of the software I added code which created an empty configuration file with defaults for all settings, many of which were a distraction as the majority of users would never change them.

More settings meant there was more scope for users to change settings which broke the device samples and the gateway.

I have removed the code to generate the full configuration file (starting with Azure IOT Hub field gateway) and included a sample configuration file with the minimum required settings in the GitHub repositories and installers.

I am assuming that if a user wants to change advanced settings they can look at the code and/or documentation and figure out the setting names and valid values.

The new sample configuration file for a Azure IoT Hub telemetry only gateway is

{
  "AzureIoTHubDeviceConnectionString": "Azure IOT Hub connection string",
  "AzureIoTHubTransportType": "amqp",
  "SensorIDIsDeviceIDSensorID": false,
  "Address": "Device address",
  "Frequency": 915000000.0
}

The prebuilt installers available on GitHub post version 1.0.13.0 (Azure IoT Hub) and 1.0.5.0 (Adafruit.IO) will implement this model.

Carbon Dioxide Sensor(MH-Z16) library comparison

The first library I looked at was for the DFRobot Gravity: UART Infrared CO2 Sensor (0-50000ppm). There was sample code provided on the associated wiki page. The code worked first time I ran it but I didn’t use this library due to the lack of checksum & packet header/footer validation.

/***************************************************
* Infrared CO2 Sensor 0-50000ppm(Wide Range)
* ****************************************************
* The follow example is used to detect CO2 concentration.
  
* @author lg.gang(lg.gang@qq.com)
* @version  V1.0
* @date  2016-6-6
  
* GNU Lesser General Public License.
* See <http://www.gnu.org/licenses/> for details.
* All above must be included in any redistribution
* ****************************************************/ 
#include <SoftwareSerial.h>
SoftwareSerial mySerial(10, 11); // RX, TX
unsigned char hexdata[9] = {0xFF,0x01,0x86,0x00,0x00,0x00,0x00,0x00,0x79}; //Read the gas density command /Don't change the order
void setup() {
  
  Serial.begin(9600);
  while (!Serial) {

  }
  mySerial.begin(9600);

}

void loop() {
   mySerial.write(hexdata,9);
   delay(500);

 for(int i=0,j=0;i<9;i++)
 {
  if (mySerial.available()>0)
  {
     long hi,lo,CO2;
     int ch=mySerial.read();

    if(i==2){     hi=ch;   }   //High concentration
    if(i==3){     lo=ch;   }   //Low concentration
    if(i==8) {
               CO2=hi*256+lo;  //CO2 concentration
      Serial.print("CO2 concentration: ");
      Serial.print(CO2);
      Serial.println("ppm");      
      }
    }   
  } 
}

After some GitHub searching the second library I looked at was abbozza_CO2_MHZ16_arduino by Michael Brinkmeier. This library appears to be “plug-in” module for the abbozza! framework. I didn’t use this library due to the lack of checksum & packet header/footer validation.

/**
 * @license
 * abbozza! Calliope plugin for the MH-Z16 CO2 sensor
 * 
 * The sensor has to be connected to a serial connection with 9600 baud.
 *
 * Copyright 2015 Michael Brinkmeier ( michael.brinkmeier@uni-osnabrueck.de )
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#include "SoftwareSerial.h"
#include "MHZ16.h"
#include "Arduino.h"

MHZ16::MHZ16(int tx, int rx) {
    this->serial = new SoftwareSerial(rx,tx,false);
    this->serial->begin(9600);
}


void MHZ16::calibrate() {
    int idx;
    for (idx = 0; idx < 9; idx++) {
        serial->write(cal[idx]);
    }
    delay(10);
}

void MHZ16::doMeasurement() {
    int idx;
    int bu;

    for (idx = 0; idx < 9; idx++) {
        serial->write(cmd[idx]);
    }
    delay(10);

    while (serial->available()) {
        do {
            bu = serial->read();
        } while (bu != 255);
        buf[0] = bu;

        idx = 1;
        while (serial->available() && (idx < 9)) {
            bu = serial->read();
            buf[idx] = bu;
            idx++;
        }

        if (idx == 9) {
            PPM = ((int) buf[2]) *256 + ((int) buf[3]);
        }
    }
}

int MHZ16::getPPM() {
    return PPM;
}

The third library was produced by Sandbox electronics for their selection of 10,000PPM thru 100,000PPM MH-Z16 sensors. Their datasheet looked similar(maybe newer?) to the Seeedstudio one and the packet format was the same.

Their library had checksum & packet header/footer validation but I didn’t use it because the carbon dioxide concentration was calculated using 4 bytes (maybe this was to support the different range sensors?)

/*
Description:
This is a example code for Sandbox Electronics NDIR CO2 sensor module.
You can get one of those products on
http://sandboxelectronics.com

Version:
V1.2

Release Date:
2019-01-10

Author:
Tiequan Shao          support@sandboxelectronics.com

Lisence:
CC BY-NC-SA 3.0

Please keep the above information when you use this code in your project.
*/

#include <SoftwareSerial.h>
#include <NDIR_SoftwareSerial.h>
#define  RECEIVE_TIMEOUT  (100)

#if ARDUINO >= 100
    #include "Arduino.h"
#else
    #include "WProgram.h"
#endif

class SoftwareSerial;

uint8_t NDIR_SoftwareSerial::cmd_measure[9]                = {0xFF,0x01,0x9C,0x00,0x00,0x00,0x00,0x00,0x63};
uint8_t NDIR_SoftwareSerial::cmd_calibrateZero[9]          = {0xFF,0x01,0x87,0x00,0x00,0x00,0x00,0x00,0x78};
uint8_t NDIR_SoftwareSerial::cmd_enableAutoCalibration[9]  = {0xFF,0x01,0x79,0xA0,0x00,0x00,0x00,0x00,0xE6};
uint8_t NDIR_SoftwareSerial::cmd_disableAutoCalibration[9] = {0xFF,0x01,0x79,0x00,0x00,0x00,0x00,0x00,0x86};

NDIR_SoftwareSerial::NDIR_SoftwareSerial(uint8_t rx_pin, uint8_t tx_pin) : serial(rx_pin, tx_pin, false)
{
}


uint8_t NDIR_SoftwareSerial::begin()
{
    serial.begin(9600);

    if (measure()) {
        return true;
    } else {
        return false;
    }
}

uint8_t NDIR_SoftwareSerial::measure()
{
    uint8_t i;
    uint8_t buf[9];
    uint32_t start = millis();

    serial.flush();

    for (i=0; i<9; i++) {
        serial.write(cmd_measure[i]);
    }

    for (i=0; i<9;) {
        if (serial.available()) {
            buf[i++] = serial.read();
        }

        if (millis() - start > RECEIVE_TIMEOUT) {
            return false;
        }
    }

    if (parse(buf)) {
        return true;
    }

    return false;
}


void NDIR_SoftwareSerial::calibrateZero()
{
    uint8_t i;

    for (i=0; i<9; i++) {
        serial.write(cmd_calibrateZero[i]);
    }
}


void NDIR_SoftwareSerial::enableAutoCalibration()
{
    uint8_t i;

    for (i=0; i<9; i++) {
        serial.write(cmd_enableAutoCalibration[i]);
    }
}


void NDIR_SoftwareSerial::disableAutoCalibration()
{
    uint8_t i;

    for (i=0; i<9; i++) {
        serial.write(cmd_disableAutoCalibration[i]);
    }
}


uint8_t NDIR_SoftwareSerial::parse(uint8_t *pbuf)
{
    uint8_t i;
    uint8_t checksum = 0;

    for (i=0; i<9; i++) {
        checksum += pbuf[i];
    }

    if (pbuf[0] == 0xFF && pbuf[1] == 0x9C && checksum == 0xFF) {
        ppm = (uint32_t)pbuf[2] << 24 | (uint32_t)pbuf[3] << 16 | (uint32_t)pbuf[4] << 8 | pbuf[5];
        return true;
    } else {
        return false;
    }
}

The forth library I looked at was MHZ-Z-C02-Sensors by Tobias Schürg this library was for different series of MHZ sensors. With re-synching, configurable timeouts and checksum validation it looked like the code could easily be adapted for the MH-Z16.

/* MHZ library

    By Tobias Schürg
*/

#include "MHZ.h"

const int MHZ14A = 14;
const int MHZ19B = 19;

const int MHZ14A_RESPONSE_TIME = 60;
const int MHZ19B_RESPONSE_TIME = 120;

const int STATUS_NO_RESPONSE = -2;
const int STATUS_CHECKSUM_MISMATCH = -3;
const int STATUS_INCOMPLETE = -4;
const int STATUS_NOT_READY = -5;

unsigned long lastRequest = 0;

MHZ::MHZ(uint8_t rxpin, uint8_t txpin, uint8_t pwmpin, uint8_t type)
    : co2Serial(rxpin, txpin) {
  _rxpin = rxpin;
  _txpin = txpin;
  _pwmpin = pwmpin;
  _type = type;

  co2Serial.begin(9600);
}

/**
 * Enables or disables the debug mode (more logging).
 */
void MHZ::setDebug(boolean enable) {
  debug = enable;
  if (debug) {
    Serial.println(F("MHZ: debug mode ENABLED"));
  } else {
    Serial.println(F("MHZ: debug mode DISABLED"));
  }
}

boolean MHZ::isPreHeating() {
  if (_type == MHZ14A) {
    return millis() < (3 * 60 * 1000);
  } else if (_type == MHZ19B) {
    return millis() < (3 * 60 * 1000);
  } else {
    Serial.println(F("MHZ::isPreHeating() => UNKNOWN SENSOR"));
    return false;
  }
}

boolean MHZ::isReady() {
  if (isPreHeating()) return false;
  if (_type == MHZ14A)
    return lastRequest < millis() - MHZ14A_RESPONSE_TIME;
  else if (_type == MHZ19B)
    return lastRequest < millis() - MHZ19B_RESPONSE_TIME;
  else {
    Serial.print(F("MHZ::isReady() => UNKNOWN SENSOR \""));
    Serial.print(_type);
    Serial.println(F("\""));
    return true;
  }
}

int MHZ::readCO2UART() {
  if (!isReady()) return STATUS_NOT_READY;
  if (debug) Serial.println(F("-- read CO2 uart ---"));
  byte cmd[9] = {0xFF, 0x01, 0x86, 0x00, 0x00, 0x00, 0x00, 0x00, 0x79};
  byte response[9];  // for answer

  if (debug) Serial.print(F("  >> Sending CO2 request"));
  co2Serial.write(cmd, 9);  // request PPM CO2
  lastRequest = millis();

  // clear the buffer
  memset(response, 0, 9);

  int waited = 0;
  while (co2Serial.available() == 0) {
    if (debug) Serial.print(".");
    delay(100);  // wait a short moment to avoid false reading
    if (waited++ > 10) {
      if (debug) Serial.println(F("No response after 10 seconds"));
      co2Serial.flush();
      return STATUS_NO_RESPONSE;
    }
  }
  if (debug) Serial.println();

  // The serial stream can get out of sync. The response starts with 0xff, try
  // to resync.
  // TODO: I think this might be wrong any only happens during initialization?
  boolean skip = false;
  while (co2Serial.available() > 0 && (unsigned char)co2Serial.peek() != 0xFF) {
    if (!skip) {
      Serial.print(F("MHZ: - skipping unexpected readings:"));
      skip = true;
    }
    Serial.print(" ");
    Serial.print(co2Serial.peek(), HEX);
    co2Serial.read();
  }
  if (skip) Serial.println();

  if (co2Serial.available() > 0) {
    int count = co2Serial.readBytes(response, 9);
    if (count < 9) {
      co2Serial.flush();
      return STATUS_INCOMPLETE;
    }
  } else {
    co2Serial.flush();
    return STATUS_INCOMPLETE;
  }

  if (debug) {
    // print out the response in hexa
    Serial.print(F("  << "));
    for (int i = 0; i < 9; i++) {
      Serial.print(response[i], HEX);
      Serial.print(F("  "));
    }
    Serial.println(F(""));
  }

  // checksum
  byte check = getCheckSum(response);
  if (response[8] != check) {
    Serial.println(F("MHZ: Checksum not OK!"));
    Serial.print(F("MHZ: Received: "));
    Serial.println(response[8], HEX);
    Serial.print(F("MHZ: Should be: "));
    Serial.println(check, HEX);
    temperature = STATUS_CHECKSUM_MISMATCH;
    co2Serial.flush();
    return STATUS_CHECKSUM_MISMATCH;
  }

  int ppm_uart = 256 * (int)response[2] + response[3];

  temperature = response[4] - 44;  // - 40;

  byte status = response[5];
  if (debug) {
    Serial.print(F(" # PPM UART: "));
    Serial.println(ppm_uart);
    Serial.print(F(" # Temperature? "));
    Serial.println(temperature);
  }

  // Is always 0 for version 14a  and 19b
  // Version 19a?: status != 0x40
  if (debug && status != 0) {
    Serial.print(F(" ! Status maybe not OK ! "));
    Serial.println(status, HEX);
  } else if (debug) {
    Serial.print(F(" Status  OK: "));
    Serial.println(status, HEX);
  }

  co2Serial.flush();
  return ppm_uart;
}

uint8_t MHZ::getLastTemperature() {
  if (isPreHeating()) return STATUS_NOT_READY;
  return temperature;
}

byte MHZ::getCheckSum(byte* packet) {
  if (debug) Serial.println(F("  getCheckSum()"));
  byte i;
  unsigned char checksum = 0;
  for (i = 1; i < 8; i++) {
    checksum += packet[i];
  }
  checksum = 0xff - checksum;
  checksum += 1;
  return checksum;
}

int MHZ::readCO2PWM() {
  // if (!isReady()) return STATUS_NOT_READY; not needed?
  if (debug) Serial.print(F("-- reading CO2 from pwm "));
  unsigned long th, tl, ppm_pwm = 0;
  do {
    if (debug) Serial.print(".");
    th = pulseIn(_pwmpin, HIGH, 1004000) / 1000;
    tl = 1004 - th;
    ppm_pwm = 5000 * (th - 2) / (th + tl - 4);
  } while (th == 0);
  if (debug) {
    Serial.print(F("\n # PPM PWM: "));
    Serial.println(ppm_pwm);
  }
  return ppm_pwm;
}

The forth library I looked at was MHZ16_uart by Intar it had been updated recently, was quite lightweight, had timeouts, checksum & packet header/footer validation.

/*
  MHZ16_uart.cpp - MH-Z16 CO2 sensor library for ESP-32
  by Intar BV
  version 0.1
  
  License MIT
*/

#include "MHZ16_uart.h"
#include "Arduino.h"


#define WAIT_READ_TIMES	100
#define WAIT_READ_DELAY	10

// public

MHZ16_uart::MHZ16_uart(){
}
MHZ16_uart::MHZ16_uart(int rx, int tx){
	begin(rx,tx);
}

MHZ16_uart::~MHZ16_uart(){
}

#ifdef ARDUINO_ARCH_ESP32
void MHZ16_uart::begin(int rx, int tx, int s){
	_rx_pin = rx;
	_tx_pin = tx;
	_start_millis = millis();
	_serialno = s;
}
#else
void MHZ16_uart::begin(int rx, int tx){
	_rx_pin = rx;
	_start_millis = millis();
	_tx_pin = tx;
}
#endif

void MHZ16_uart::calibrateZero() {
	writeCommand( zerocalib );
}

void MHZ16_uart::calibrateSpan(int ppm) {
	if( ppm < 1000 )	return;

	uint8_t com[MHZ16_uart::REQUEST_CNT];
	for(int i=0; i<MHZ16_uart::REQUEST_CNT; i++) {
		com[i] = spancalib[i];
	}
	com[3] = (uint8_t)(ppm/256);
	com[4] = (uint8_t)(ppm%256);
	writeCommand( com );
}

int MHZ16_uart::getPPM() {
	return getSerialData();
}

boolean MHZ16_uart::isWarming(){
	return millis() <= _start_millis + PREHEAT_MS;
}

//protected
void MHZ16_uart::writeCommand(uint8_t cmd[]) {
	writeCommand(cmd,NULL);
}

void MHZ16_uart::writeCommand(uint8_t cmd[], uint8_t* response) {
#ifdef ARDUINO_ARCH_ESP32
	HardwareSerial hserial(_serialno);
	hserial.begin(9600, SERIAL_8N1, _rx_pin, _tx_pin);
#else
	SoftwareSerial hserial(_rx_pin, _tx_pin);
	hserial.begin(9600);
#endif
    hserial.write(cmd, REQUEST_CNT);
	hserial.write(MHZ16_checksum(cmd));
	hserial.flush();
	
	if (response != NULL) {
		int i = 0;
		while(hserial.available() <= 0) {
			if( ++i > WAIT_READ_TIMES ) {
				Serial.println("error: can't get MH-Z16 response.");
				return;
			}
			yield();
			delay(WAIT_READ_DELAY);
		}
		hserial.readBytes(response, MHZ16_uart::RESPONSE_CNT);
	}

}

//private

int MHZ16_uart::getSerialData() {
	uint8_t buf[MHZ16_uart::RESPONSE_CNT];
	for( int i=0; i<MHZ16_uart::RESPONSE_CNT; i++){
		buf[i]=0x0;
	}

	writeCommand(getppm, buf);
	int co2 = 0, co2temp = 0, co2status =  0;

	// parse
	if (buf[0] == 0xff && buf[1] == 0x86 && MHZ16_checksum(buf) == buf[MHZ16_uart::RESPONSE_CNT-1]) {
		co2 = buf[2] * 256 + buf[3];
	} else {
		co2 = co2temp = co2status = -1;
	}
	return co2;
}	

uint8_t MHZ16_uart::MHZ16_checksum( uint8_t com[] ) {
	uint8_t sum = 0x00;
	for ( int i = 1; i < MHZ16_uart::REQUEST_CNT; i++) {
		sum += com[i];
	}
	sum = 0xff - sum + 0x01;
	return sum;
}

It ran second time on one of my Arduino devices (after I figured out how to configure the serial port pins) and though intended for an ESP8266 device this is the library I will field test.

#include <MHZ16_uart.h>

//Select 2 digital pins as SoftwareSerial's Rx and Tx. For example, Rx=2 Tx=3
MHZ16_uart mySensor(4,5);

void setup()
{
  Serial.begin(9600);

  mySensor.begin(4,5); 
}


void loop() 
{
  if ( !mySensor.isWarming())
  {
    Serial.print("CO2 Concentration is ");
    Serial.print(mySensor.getPPM());
    Serial.println("ppm");
  }
  else
{
    Serial.println("isWarming");
  }
  
  delay(10000);
}

This was just a sample of the libraries I found on GitHub if I missed a good a library contact me via the comments.