1 /*
 2     Measurement of CO2 concentration using MH-Z14 sensor
 3 */ 
 4 #include <SoftwareSerial.h>
 5 
 6 byte cmd[] = {0xFF, 0x01, 0x86, 0x00, 0x00, 0x00, 0x00, 0x00, 0x79};
 7 byte buffer[20]; 
 8 
 9 int backNum = 0;
10 int co2 = 0; //ppm
11 
12 SoftwareSerial mySerial(2, 3); // RX, TX
13 
14 void setup()
15 {
16     Serial.begin(9600);
17     
18     // set the data rate for the SoftwareSerial port
19     mySerial.begin(9600);
20     mySerial.listen();
21 }
22 
23 void loop()
24 {
25     // send the command
26     for(int i = 0; i < sizeof(cmd); i++)
27     {
28         mySerial.write(cmd[i]);
29     }
30 
31     delay(100);
32     backNum = mySerial.available();
33 
34     // get the result
35     for(int i = 0; i < backNum; i++)
36     {
37         buffer[i] = mySerial.read();
38     }
39     co2 = buffer[2]*256 + buffer[3];
40 
41     // print
42     Serial.print("CO2 = "); Serial.print(co2); Serial.print(" ppm   ");
43     
44     // check the value
45     if ((buffer[1] == 0x86) && (CheckVal(buffer, 9) == 0xFF))
46     {
47         Serial.println("value checked.");
48     }
49     else
50     {
51         Serial.println("error");
52     }
53 
54     delay(2000);
55 }
56 
57 byte CheckVal(byte data[], byte len)
58 {
59     byte result = 0;
60     for(int i = 0; i < len; i++)
61     {
62         result = result + data[i];
63     }
64     return result;
65 }