MH-Z14 Intelligent Infrared Gas Module User’s Manual

MH-Z14 Intelligent Infrared Gas Module

Profile

Main functions and features：

• High sensitivity, High resolution
• Low power consumption
• Output modes: UART, analog voltage signal, PWM wave
• Quick response
• Temperature compensation, excellent linear output
• Good stability
• Long lifespan
• Anti-water vapor interference
• No poisoning
  

Main technical parameters

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

1. General Settings
   Baud rate| 9600
   ---|---
   Date byte| 8 byte
   Stop byte| 1byte
   Calibrate byte| no
2. 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 end Command 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

3. 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

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