Winsen MH-Z19B, User Manual, Page: 8 / 10

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8.Zero Point Calibration
About zero point calibration:
This module has three methods for zero point calibration: hand-operated method, sending command method
and self-calibration. All the zero point is at 400ppm CO2.
Hand-operated method : Connect module’s HD pin to low level(0V), lasting for 7 seconds at least. Before
calibrating the zero point, please ensure that the sensor is stable for more than 20 minutes at 400ppm ambient
environment.
Note: Detection range should be 0~2000, 0~5000, or 0~10000ppm.
For example: set 0~2000ppm detection range, send command: FF 01 99 00 00 00 07 D0 8F
set 0~10000ppm detection range, send command: FF 01 99 00 00 00 27 10 2F
Analog Voltage Output(Vo)
Conversion between analog voltage output and concentration, take 0.4V~2V as an example:
Vo (V)=0.4V+(2.0V-0.4V)*C(concentration ppm) / detection range(ppm)
1. Checksum calculation method
Checksum = (Negative (Byte1+Byte2+Byte3+Byte4+Byte5+Byte6+Byte7))+1
For example:
Byte0 Byte1 Byte2 Byte3 Byte4 Byte5 Byte6 Byte7 Byte8
Start Byte Reserved Command - - - - - Check
sum
0xFF 0x01 0x86 0x00 0x00 0x00 0x00 0x00 Check
sum
Calculating Checksum
：
1
、
Add Byte 1 to Byte 7: 0x01 + 0x86 + 0x00 + 0x00 + 0x00 + 0x00 + 0x00 = 0x87
2
、
Negative: 0xFF - 0x87 = 0x78
3
、
Then+1
：
0x78 + 0x01 = 0x79

C language
char getCheckSum(char *packet)
{
char i, checksum;
for( i = 1; i < 8; i++)
{
ch= packet[i];
}
checksum = 0xff
– checksum;
ch= 1;
return checksum;
}