mh-z14-calibration-test.pde

//
// mh-z14-calibration-test.pde
//
// see also... https://www.openhacks.com/uploadsproductos/mh-z14_co2.pdf
//
import processing.serial.*;

byte [] buf = new byte[9];
Serial s = new Serial(this, "COM9", 9600);

// calibrate zero point
s.write(0xff);  // header
s.write(0x01);  // sensor no
s.write(0x87);  // command
s.write(0x00);
s.write(0x00);
s.write(0x00);
s.write(0x00);
s.write(0x00);
s.write(0x78);  // check value
delay(500);

// read return value (9byte)
print("read value : ");
for (int i = 0; i < 9; ++i) {
  buf[i] = (byte)s.read();
  print(hex(buf[i]));
  print(", ");
}
println();

// read gas soncentration
s.write(0xff);  // header
s.write(0x01);  // sensor no
s.write(0x86);  // command
s.write(0x00);
s.write(0x00);
s.write(0x00);
s.write(0x00);
s.write(0x00);
s.write(0x79);  // check value
delay(500);

// read return value (9byte)
print("read value : ");
for (int i = 0; i < 9; ++i) {
  buf[i] = (byte)s.read();
  print(hex(buf[i]));
  print(", ");
}
println();

int val = Byte.toUnsignedInt(buf[2]) * 256 + Byte.toUnsignedInt(buf[3]);
println("co2=" + val);