Add Support for MH-Z19C CO2 Sensor

lib/MHZ19C/MHZ19C.cpp

@@ -0,0 +1,103 @@
+/*
+  MHZ19C.cpp - MHZ19C Sensor Library
+  Copyright (c) 2020-2021, Stefan Brand
+  All rights reserved.
+  Redistribution and use in source and binary forms, with or without
+  modification, are permitted provided that the following conditions are met:
+  1. Redistributions of source code must retain the above copyright notice, this
+     list of conditions and the following disclaimer.
+  2. Redistributions in binary form must reproduce the above copyright notice,
+     this list of conditions and the following disclaimer in the documentation
+     and/or other materials provided with the distribution.
+  3. Neither the name of the copyright holder nor the names of its
+     contributors may be used to endorse or promote products derived from
+     this software without specific prior written permission.
+  THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+  AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+  IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+  DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+  FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+  DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+  SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+  CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+  OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+  OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+*/
+
+#include <Arduino.h>
+#include "MHZ19C.h"
+
+// Constructor - Inititalize Hardware UART
+MHZ19C::MHZ19C(void) {
+    Serial.begin(9600);
+    Serial.setTimeout(MHZ19C_READ_TIMEOUT);
+}
+
+void MHZ19C::getSensorData(lora_data &loradata) {
+    write(MHZ19C_CMD_GET_PPM, 0x00);
+    delay(50);
+    uint8_t readBytes = read();
+    
+    loradata.ppm = 0;
+    if (readBytes > 0) {
+        switch(buffer[1]) {
+            case 0x86:
+                loradata.ppm = (buffer[2]*256) + buffer[3];
+                break;
+        }
+    }
+}
+
+// Turn Self Calibration Routine On or Off
+void MHZ19C::setSelfCalibration(bool state) {
+  if (state) {
+    write(0x79, 0xA0);
+  } else {
+    write(0x79, 0x00);
+  }
+}
+
+// Write a Command to the Sensor
+void MHZ19C::write(uint8_t cmd, uint8_t arg) {
+    uint8_t _cmd[9] = {0xFF, 0x01, cmd, arg, 0x00, 0x00, 0x00, 0x00, 0x00};
+    uint8_t crc = crc8(_cmd);
+    _cmd[8] = crc;
+    while (Serial.available() > 0) Serial.read();
+    Serial.write(_cmd, 9);
+    Serial.flush();
+}
+
+// Read a Sensor Response
+uint8_t MHZ19C::read() {
+    uint8_t ret = 0;
+    zeroBuffer();
+
+    // Read Available Bytes
+    if (Serial.available() > 0) {
+      ret = Serial.readBytes(buffer, MHZ19C_SER_BUF_LEN);
+    }
+    
+    // Check Sync Bit and CRC
+    if (buffer[0] != 0xFF || buffer [8] != crc8(buffer))
+      return 0;   
+    
+    // Return Read Bytes
+    return ret;
+}
+
+// Fill the Internal Buffer with Zeroes
+void MHZ19C::zeroBuffer() {
+  for (int i=0; i < MHZ19C_SER_BUF_LEN; i++)
+    buffer[i] = 0x00;
+}
+
+// Calculate 8Bit CRC of Messages and Commands
+uint8_t MHZ19C::crc8(uint8_t *paket){
+  uint8_t i, checksum = 0x00;
+  for( i = 1; i < 8; i++)
+    checksum += paket[i];
+
+  checksum  = 0xff - checksum;
+  checksum += 1;
+  return checksum;
+}

lib/MHZ19C/MHZ19C.h

@@ -0,0 +1,58 @@
+/*
+  MHZ19C.h - MHZ19C Sensor Library
+  Copyright (c) 2020-2021, Stefan Brand
+  All rights reserved.
+  Redistribution and use in source and binary forms, with or without
+  modification, are permitted provided that the following conditions are met:
+  1. Redistributions of source code must retain the above copyright notice, this
+     list of conditions and the following disclaimer.
+  2. Redistributions in binary form must reproduce the above copyright notice,
+     this list of conditions and the following disclaimer in the documentation
+     and/or other materials provided with the distribution.
+  3. Neither the name of the copyright holder nor the names of its
+     contributors may be used to endorse or promote products derived from
+     this software without specific prior written permission.
+  THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+  AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+  IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+  DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+  FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+  DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+  SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+  CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+  OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+  OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+*/
+
+#ifndef MHZ19C_H
+#define MHZ19C_H
+
+// Data Structure for the LoRa Packet
+struct lora_data {
+  uint8_t bat;
+  int16_t ppm;
+} __attribute__ ((packed));
+
+#define MHZ19C_READ_TIMEOUT 500  // Timeout for Serial Communication
+#define MHZ19C_SER_BUF_LEN  9    // Length of the Internal Serial Message Buffer
+
+#define MHZ19C_CMD_SET_AUTOCAL 0x79  // Turn Self Calibration on/off
+#define MHZ19C_CMD_GET_PPM     0x86  // Get Current PPM Reading
+
+class MHZ19C {
+  private:
+    uint8_t buffer[MHZ19C_SER_BUF_LEN];
+
+    void write(byte cmd, byte arg);
+    uint8_t read();
+    void zeroBuffer(void);
+    uint8_t crc8(uint8_t *paket);
+    uint16_t getPPM(void);
+
+  public:
+    MHZ19C(void);
+    void getSensorData(lora_data &loradata);
+    void setSelfCalibration(bool state);
+};
+
+#endif

lib/SG112A/SG112A.cpp

@@ -1,6 +1,33 @@
+/*
+  SG112A.cpp - SG112A Sensor Library
+  Copyright (c) 2020-2021, Stefan Brand
+  All rights reserved.
+  Redistribution and use in source and binary forms, with or without
+  modification, are permitted provided that the following conditions are met:
+  1. Redistributions of source code must retain the above copyright notice, this
+     list of conditions and the following disclaimer.
+  2. Redistributions in binary form must reproduce the above copyright notice,
+     this list of conditions and the following disclaimer in the documentation
+     and/or other materials provided with the distribution.
+  3. Neither the name of the copyright holder nor the names of its
+     contributors may be used to endorse or promote products derived from
+     this software without specific prior written permission.
+  THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+  AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+  IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+  DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+  FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+  DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+  SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+  CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+  OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+  OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+*/
+
 #include <Arduino.h>
 #include "SG112A.h"
 
+// Constructor - Inititalize Hardware UART
 SG112A::SG112A(void) {
     Serial.begin(9600);
     Serial.setTimeout(READ_TIMEOUT);
@@ -20,6 +47,7 @@ void SG112A::getSensorData(lora_data &loradata) {
     }
 }
 
+// Write a Command to the Sensor
 void SG112A::write(byte cmd) {
     uint8_t _cmd[6] = {0xAA, 0x55, cmd, 0x00, 0x00, 0x00};
     uint16_t crc = crc16(_cmd, 4);
@@ -30,26 +58,37 @@ void SG112A::write(byte cmd) {
     Serial.flush();
 }
 
+// Read a Sensor Response
 uint8_t SG112A::read() {
+    // Number of returned Bytes
     uint8_t ret = 0;
+    // Clear Internal Buffer
     zeroBuffer();
+
+    // Read Available Bytes
     if (Serial.available() > 0) {
       ret = Serial.readBytes(buffer, SER_BUF_LEN);
     }
 
-    if (buffer[0] != 0xBB && buffer[1] != 0x66)
-        ret = 0;
+    // Check Sync Bytes
+    if (buffer[0] != 0xBB || buffer[1] != 0x66)
+      return 0;
    
-    // TODO: Do CRC Check Here
+    // Check CRC of the Returned Messages
+    uint16_t crc = crc16(buffer, ret-2);
+    if (buffer[ret-1] != (uint8_t)(crc >> 8) || buffer[ret-2] != (uint8_t)(crc & 0xFF))
+      return 0;
 
     return ret;
 }
 
+// Fill the Internal Buffer with Zeroes
 void SG112A::zeroBuffer() {
     for (int i=0; i < SER_BUF_LEN; i++)
         buffer[i] = 0x00;
 }
 
+// Calculate 16Bit CRC of Messages and Commands
 uint16_t SG112A::crc16(uint8_t *cmd, int len){
   uint16_t ret = 0xffff;
   uint16_t polynomial = 0xa001;

lib/SG112A/SG112A.h

@@ -1,17 +1,44 @@
+/*
+  SG112A.h - SG112A Sensor Library
+  Copyright (c) 2020-2021, Stefan Brand
+  All rights reserved.
+  Redistribution and use in source and binary forms, with or without
+  modification, are permitted provided that the following conditions are met:
+  1. Redistributions of source code must retain the above copyright notice, this
+     list of conditions and the following disclaimer.
+  2. Redistributions in binary form must reproduce the above copyright notice,
+     this list of conditions and the following disclaimer in the documentation
+     and/or other materials provided with the distribution.
+  3. Neither the name of the copyright holder nor the names of its
+     contributors may be used to endorse or promote products derived from
+     this software without specific prior written permission.
+  THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+  AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+  IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+  DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+  FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+  DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+  SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+  CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+  OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+  OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+*/
+
 #ifndef SG112A_H
 #define SG112A_H
 
+// Data Structure for the LoRa Packet
 struct lora_data {
   uint8_t bat;
   int16_t ppm;
 } __attribute__ ((packed));
 
-#define READ_TIMEOUT 500
-#define SER_BUF_LEN  16
+#define READ_TIMEOUT 500  // Timeout for Serial Communication
+#define SER_BUF_LEN  16   // Length of the Internal Serial Message Buffer
 
-#define CMD_GET_VER 0x10
-#define CMD_GET_SER 0x12
-#define CMD_GET_PPM 0x14
+#define CMD_GET_VER 0x10  // Get Sensor Version
+#define CMD_GET_SER 0x12  // Get Sensor Serial
+#define CMD_GET_PPM 0x14  // Get Current PPM Reading
 
 class SG112A {
   private:

src/config.h.example

@@ -11,6 +11,7 @@
 #define HAS_BME280
 // #define HAS_SHT21
 // #define HAS_SG112A
+// #define HAS_MHZ19C
 // #define HAS_NO_SENSOR
 
 // How many minutes to sleep between Measuring/Sending

src/main.cpp

@@ -35,6 +35,9 @@ void blink(uint8_t num) {
   struct lora_data {
     uint8_t bat;
   } __attribute ((packed));
+#elif defined HAS_MHZ19C
+  #include <MHZ19C.h>
+  MHZ19C sensor;
 #elif defined HAS_SG112A
   #include <SG112A.h>
   SG112A sensor;
@@ -71,7 +74,7 @@ const lmic_pinmap lmic_pins = {
 };
 
 // List of unused Pins - will be disabled for Power Saving
-#if defined DEBUG || defined HAS_SG112A
+#if defined DEBUG || defined HAS_SG112A || defined HAS_MHZ19C
 const int disabledPins[] = {PIN_PB5, PIN_PB4, PIN_PB1, PIN_PB0, PIN_PC3, PIN_PC2, PIN_PC1, PIN_PC0};
 #else
 const int disabledPins[] = {PIN_PB5, PIN_PB4, PIN_PB3, PIN_PB2, PIN_PB1, PIN_PB0, PIN_PC3, PIN_PC2, PIN_PC1, PIN_PC0};