MH-Z14 Intelligent Infrared Gas Module User's Manual

Working voltage	4.5 V ~ 5.5V DC
Average current	< 85 mA
Interface level	3.3 V
Measuring range	0~5%VOL optional
Output signal	PWM
	UART
	0.4-2V DC
Preheat time	3min
Reponse Time	T90 < 90s
Working temperature	0℃ ~ 50℃
Working humidity	0~95%RH
Weight	15 g
Lifespan	>5 year
Dimension	57.5×34.7×16mm（L×W×H）

Target Gas	Measuring Range	Accuracy	Mark
Carbon Dioxide (CO2)	0~2000ppm	±(50ppm +5%readin g value)	Temperature compensation
	0~5000ppm		Temperature compensation
	0~1%VOL		Temperature compensation
	0~3%VOL		Temperature compensation
	0~5%VOL		Temperature compensation

Structure

Definition for pins

PIN	Description
Pad1、 Pad15、Pad17	Vin（input voltage 4.5V～5.5V）
Pad2、Pad3、 Pad12、Pad16	GND
Pad4	Vout2 (0.4～2V)
Pad5	Vout1 (0～2.5V)
Pad6	PWM
Pad8	HD
Pad7、 Pad9	NC
Pad11、Pad14、Pad18	UART（RXD） 0～3.3V input digital
Pad10、Pad13、Pad19	UART（TXD） 0～3.3V output digital

Circuit

Operating instruction

Analog output connections

The output value of Vout1 is 0-2.5V, which stands for 0 to full range.
The output value of Vout2 is 0.4-2V, which stands for 0 to full range.

Vin –5V
GND- Power Ground
Vout2-ADC input
After preheating, the value of output voltage from Vout2 represents gas concentration.

PWM output (taking PWM output from 2000ppm as example):

CO2 output range: 0ppm-2000ppm
Cycle: 1004ms±5%

High level output for beginning: 2ms (in name)
Middle of cycle: 1000ms±5%
Low level output for ending: 2ms（in name）
Account formula for CO2 concentration which gets through PWM:

Digital connects

Vin-5V power
GND- Power Ground
RXD connect sensor TXD
TXD connect sensor RXD
You can read gas concentration via Uart, no need to calculate.

Communication protocol

General Settings

Baud rate 9600

Date byte 8 byte

Stop byte 1byte

Calibrate byte no

Command
Each command or return：
Contains 9 bytes (byte 0 ~ 8) starting byte fixed 0 XFF
command contains sensor number (factory default to 0 x01) to check and endCommand List:

0x86	Gas concentration
0x87	Calibrate zero point（ZERO）
0x88	Calibrate span point（SPAN）

Read gas concentration

Send command
Byte0	Byte1	Byte2	Byte3	Byte4	Byte5	Byte6	Byte7	Byte8
Starting byte	Sensor No.	command	–	–	–	–	–	Check value
0XFF	0x01	0x86	0x00	0x00	0x00	0x00	0x00	0x79

Return value

Return
Byte0	Byte1	Byte2	Byte3	Byte4	Byte5	Byte6	Byte7	Byte8
Starting byte	command	High level concentration	Low level concentration	–	–	–	–	Chec k value
0XFF	0x86	0x02	0x60	0x47	0x00	0x00	0x00	0xD1

Gas concentration= high level *256+low level

Calibrate zero point

Send command
Byte0	Byte1	Byte2	Byte3	Byte4	Byte5	Byte6	Byte7	Byte8
Starting byte	Sensor No.	command	–	–	–	–	–	Check value
0XFF	0x01	0x87	0x00	0x00	0x00	0x00	0x00	0x78

No return value

Calibrate span point

Send command
Byte0	Byte1	Byte2	Byte3	Byte4	Byte5	Byte6	Byte7	Byte8
Starting byte	Sensor No.	command	High level span point	Low level span point	–	–	–	Check value
0XFF	0x01	0x88	0x07	0xD0	0x00	0x00	0x00	0xA0

No return value

Calibration and calculation
The checksum = (invert (byte 1 +… + 7)) + 1
Reading gas concentration:

Send command
Byte0	Byte1	Byte2	Byte3	Byte4	Byte5	Byte6	Byte7	Byte8
Starting byte	Sensor No.	command	–	–	–	–	–	Check value
0XFF	0x01	0x86	0x00	0x00	0x00	0x00	0x00	0x79

Except byte 0 ,add the other bytes together
0x1 + 0x86 + 0 + 0 + 0 + 0 + 0 = 0x87
Get the value from the first step, then invert it.
0xff – 0x87 = 0x78
The second value plus one
0x78 + 0x01 = 0x79
Program :C language

char getCheckSum(char *packet)
{char i, checksum; for( i = 1; i < 8; i++)
{
checksum += packet[i];

}
checksum = 0xff – checksum;
checksum += 1;
return checksum;
}

Notes for maintenance

7.1 The sensor should be calibrated regularly. The cycle time is better to be no more than 6 months.
7.2 Do not use the sensor in the high dusty environment for long time.
7.3 Please use the sensor with correct power supply.
7.4 Forbidden to cut the sensor pin.

MH-Z14 Intelligent Infrared Gas Module User’s Manual – Download [optimized]
MH-Z14 Intelligent Infrared Gas Module User’s Manual – Download

References

User Manual

Profile

Main technical parameters