read data from mh-z19b

ambient7-arduino/arduino-ide-version/ambient7-mcu/ambient7-mcu.ino

@@ -1,30 +1,99 @@
 #include <SoftwareSerial.h>
 
+const byte CO2_RX = D6; /* MCU UART RX = sensor TX */
+const byte CO2_TX = D7; /* MCU UART TX = sensor RX */
+
+SoftwareSerial co2Serial(CO2_RX, CO2_TX);
+
 unsigned long startTime = millis();
 
 void setup() {
-  Serial.begin(9600);
-  pinMode(D3, INPUT);
+  Serial.begin(115200);
+  Serial.println("Setup: ");
+  Serial.print("CO2 RX Pin: ");
+  Serial.println(CO2_RX);
+  Serial.print("CO2 TX Pin: ");
+  Serial.println(CO2_TX);
+
+  co2Serial.begin(9600);
 }
 
 void loop() {
   Serial.println("------------------------------");
   Serial.print("Time from start: ");
   Serial.print((millis() - startTime) / 1000);
   Serial.println(" s");
-  int ppm_pwm = readCO2PWM();
+
+  int ppm_uart = readCO2UART();
+
   delay(5000);
 }
 
-int readCO2PWM() {
-  unsigned long th, tl, ppm_pwm = 0;
-  do {
-    th = pulseIn(D3, HIGH, 1004000) / 1000;
-    Serial.println("Step");
-    tl = 1004 - th;
-    ppm_pwm = 5000 * (th-2)/(th+tl-4);
-  } while (th == 0);
-  Serial.print("PPM PWM: ");
-  Serial.println(ppm_pwm);
-  return ppm_pwm;
+int readCO2UART(){
+  byte cmd[9] = {0xFF,0x01,0x86,0x00,0x00,0x00,0x00,0x00,0x79};
+  byte response[9]; // for answer
+
+  Serial.println("Sending CO2 request...");
+  co2Serial.write(cmd, 9); //request PPM CO2
+
+  // clear the buffer
+  memset(response, 0, 9);
+
+  int i = 0;
+  while (co2Serial.available() == 0) {
+    delay(1000);
+    i++;
+  }
+
+  if (co2Serial.available() > 0) {
+      co2Serial.readBytes(response, 9);
+  }
+
+  // print out the response in hex
+  for (int i = 0; i < 9; i++) {
+    Serial.print(String(response[i], HEX));
+    Serial.print("   ");
+  }
+  Serial.println("");
+
+  // checksum
+  byte check = getCheckSum(response);
+  if (response[8] != check) {
+    Serial.println("Checksum not OK!");
+    Serial.print("Received: ");
+    Serial.println(response[8]);
+    Serial.print("Should be: ");
+    Serial.println(check);
+  }
+
+  // ppm
+  int ppm_uart = 256 * (int)response[2] + response[3];
+  Serial.print("PPM UART: ");
+  Serial.println(ppm_uart);
+
+  // temp
+  byte temp = response[4] - 40;
+  Serial.print("Temperature? ");
+  Serial.println(temp);
+
+  // status
+  byte status = response[5];
+  Serial.print("Status? ");
+  Serial.println(status);
+  if (status == 0x40) {
+    Serial.println("Status OK");
+  }
+
+  return ppm_uart;
+}
+
+byte getCheckSum(byte *packet) {
+  byte i;
+  byte checksum = 0;
+  for (i = 1; i < 8; i++) {
+    checksum += packet[i];
+  }
+  checksum = 0xff - checksum;
+  checksum += 1;
+  return checksum;
 }