Winsen MH-Z19B, User Manual, Page: 7 / 10

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Software setting
Set serial port baud rate be 9600, data bit 8 bytes, stop bit 1byte, parity bit null.
Commands
0x86 Read CO2 concentration
0x87 Calibrate Zero Point (ZERO)
0x88 Calibrate Span Point (SPAN)
0x79 ON/OFF Self-calibration function for zero point
0x99 Detection range setting
0x86- Read CO2 concentration
Sending command
Byte0 Byte1 Byte2 Byte3 Byte4 Byte5 Byte6 Byte7 Byte8
Start Byte Reserved Command - - - - - Checksum
0xFF 0x01 0x86 0x00 0x00 0x00 0x00 0x00 0x79
Return value
Byte0 Byte1 Byte2 Byte3 Byte4 Byte5 Byte6 Byte7 Byte8
Start Byte Comman
d
Concentration
(High 8 Byte)
Concentration
(Low 8 Byte)
- - - - Checksum
0xFF 0x86 HIGH LOW - - - - Checksum
CO2 concentration = HIGH * 256 + LOW
For example:
Send command FF 01 86 00 00 00 00 00 79, Return value FF 86 02 20 00 00 00 00 58
How to calculate concentration: convert hexadecimal 02 into decimal 2, hexadecimal 20 into decimal 32, then 2*256+32=544ppm
0x79- On/Off Self-calibration for Zero Point
Send command-No return value
Byte0 Byte1 Byte2 Byte3 Byte4 Byte5 Byte6 Byte7 Byte8
Start Byte Reserved Command - - - - - Checksum
0xFF 0x01 0x79 0xA0/0x00 0x00 0x00 0x00 0x00 Checksum
For example:
ON this function, send command: FF 01 79 A0 00 00 00 00 E6
OFF this function, send command: FF 01 79 00 00 00 00 00 86
NOTE: This function is on when Byte3 is 0xA0 while this function is off when Byte3 is 0x00.
Default status is “this function is on”.
0x99- Detection range setting
Send command-No return value
Byte0 Byte1 Byte2 Byte3 Byte4 Byte5 Byte6 Byte7 Byte8
Start
Byte
Reserved Command Reserved Detection range
24~32 bit
Detection range
16~23 bit
Detection
range 8~15 bit
Detection
range 0~7 bit
Check
sum
0xFF 0x01 0x99 0x00 Data 1 Data 2 Data 3 Data 4 Check
sum