Internal addresses, registers, constants for the MH-Z19 CO2 sensor. More...

Detailed Description

Internal addresses, registers, constants for the MH-Z19 CO2 sensor.

Author: Koen Zandberg koen@.nosp@m.berg.nosp@m.zand..nosp@m.net

MH-Z19 Baud rate
Fixed at 9600 by design.
#define	MHZ19_UART_BAUDRATE 9600

MH-Z19 Buffer size
A transmission from the MH-Z19 is 9 bytes long: 1 Start byte 1 Sensor number 2 bytes data 4 bytes padding 1 byte checksum The start byte is not stored because it is not used in the checksum calculation.
#define	MHZ19_BUF_SIZE 8

MH-Z19 Timeout in milliseconds
20 ms gives a decent margin on top of the UART transmission time. The datasheet does not specify any timings beside the UART baud rate. A single byte takes 10 bits effectively: a start bit, 8 bits data and stop bit. 9 bytes are transmitted, thus 10 bits * 9 / 9600bps = 9.3 ms.
#define	MHZ19_TIMEOUT_READ 20

#define	MHZ19_TIMEOUT_CMD (MHZ19_TIMEOUT_READ * 5)

MH-Z19 transmission constants
#define	MHZ19_READ_START 0xff
	Start bytes.

#define	MHZ19_READ_SENSOR_NUM 0x01
	Sensor number.

MH-Z19 commands
#define	MHZ19_CMD_AUTO_CALIBRATION 0x79
	Auto calibration command.

#define	MHZ19_CMD_GAS_CONCENTRATION 0x86
	Gas concentration command.

#define	MHZ19_CMD_CALIBRATE_ZERO 0x87
	Zero calibration command.

#define	MHZ19_CMD_CALIBRATE_SPAN 0x88
	Span calibration command.

MH-Z19 transmission data positions
#define	MHZ19_RX_POS_PPM_HIGH 1
	Measurement high byte.

#define	MHZ19_RX_POS_PPM_LOW 2
	Measurement low byte.

#define	MHZ19_RX_POS_CHECKSUM 7
	Checksum position.

Macro Definition Documentation

◆ MHZ19_BUF_SIZE

#define MHZ19_BUF_SIZE 8

Definition at line 45 of file mhz19_internals.h.

◆ MHZ19_CMD_AUTO_CALIBRATION

#define MHZ19_CMD_AUTO_CALIBRATION 0x79

Auto calibration command.

Definition at line 79 of file mhz19_internals.h.

◆ MHZ19_CMD_CALIBRATE_SPAN

#define MHZ19_CMD_CALIBRATE_SPAN 0x88

Span calibration command.

Definition at line 82 of file mhz19_internals.h.

◆ MHZ19_CMD_CALIBRATE_ZERO

#define MHZ19_CMD_CALIBRATE_ZERO 0x87

Zero calibration command.

Definition at line 81 of file mhz19_internals.h.

◆ MHZ19_CMD_GAS_CONCENTRATION

#define MHZ19_CMD_GAS_CONCENTRATION 0x86

Gas concentration command.

Definition at line 80 of file mhz19_internals.h.

◆ MHZ19_READ_SENSOR_NUM

#define MHZ19_READ_SENSOR_NUM 0x01

Sensor number.

Definition at line 72 of file mhz19_internals.h.

◆ MHZ19_READ_START

#define MHZ19_READ_START 0xff

Start bytes.

Definition at line 71 of file mhz19_internals.h.

◆ MHZ19_RX_POS_CHECKSUM

#define MHZ19_RX_POS_CHECKSUM 7

Checksum position.

Definition at line 91 of file mhz19_internals.h.

◆ MHZ19_RX_POS_PPM_HIGH

#define MHZ19_RX_POS_PPM_HIGH 1

Measurement high byte.

Definition at line 89 of file mhz19_internals.h.

◆ MHZ19_RX_POS_PPM_LOW

#define MHZ19_RX_POS_PPM_LOW 2

Measurement low byte.

Definition at line 90 of file mhz19_internals.h.

◆ MHZ19_TIMEOUT_CMD

#define MHZ19_TIMEOUT_CMD (MHZ19_TIMEOUT_READ * 5)

Definition at line 65 of file mhz19_internals.h.

◆ MHZ19_TIMEOUT_READ

#define MHZ19_TIMEOUT_READ 20

Definition at line 56 of file mhz19_internals.h.

◆ MHZ19_UART_BAUDRATE

#define MHZ19_UART_BAUDRATE 9600

Definition at line 30 of file mhz19_internals.h.