06 - MQ Gas Sensor Application

This chapter describes the MQ2 gas sensor application example on the Pico-G1 expansion board — mq_sensor. It demonstrates how to read the sensor's digital output (DO) and analog output (AO) and display the gas concentration and alarm status on a TFT screen. It is a practical example for learning gas sensor monitoring.

The application source code lives in the SDK directory source/app/06_MQ_Sensor/, providing a complete GPIO and ADC reading implementation.

1 Application Overview

1.1 Features

Dual-mode reading: reads the digital output (DO) and analog output (AO) simultaneously
Concentration display: shows the gas concentration percentage on a TFT screen
Alarm monitoring: displays the gas leak alarm status in real time
Direct ADC access: accesses the LSADC registers directly through /dev/mem

1.2 Technical Specifications

Parameter	Value
`Sensor type`	MQ2 (smoke / combustible gas / LPG)
`DO interface`	GPIO0_1 (digital output)
`AO interface`	GPIO1_0/LSADC_CH0 (analog output)
`Supply voltage`	5V (required by the heater)
`ADC resolution`	12-bit (0~4095)
`Refresh interval`	200ms (configurable)

1.3 Hardware Connection

Signal	On-board GPIO	Physical pad	Description
DO	GPIO0_1	iocfg_reg1 @ 0x112C0004	Digital output (alarm threshold)
AO	GPIO1_0	iocfg_reg20 @ 0x12090000	Analog output (concentration value)
VCC	5V	—	Power supply (the heater requires 5V)
GND	GND	—	Ground

2 Build and Deployment

2.1 Building the Application

export PATH=$PATH:<SDK>/tools/linux/toolchains/arm-gcc12.2.0-linux-uclibceabi/bin
cd <SDK>/source/app/06_MQ_Sensor
make

2.2 Running the Application

scp mq_sensor root@<board-IP>:/usr/bin/
ssh root@<board-IP> '/usr/bin/mq_sensor'

3 Expected Output

3.1 Console output

/mnt # ./gas_sensor
[mq2] pad 复用：LSADC_CH0 pad (GPIO1_0) -> func4
[mq2] pad 0x12090000 -> 0x00001004
[mq2] 初始化 SPI 屏（/dev/spidev2.0）...
[spi] pad 0x100C0028 -> 0x00001004
[spi] pad 0x100C002C -> 0x00001004
[spi] pad 0x100C0030 -> 0x00001000
[spi] pad 0x100C0020 -> 0x00001005
[spi] pad 0x100C001C -> 0x00001005
[spi] opening /dev/spidev2.0 ...
[spi] spidev opened, fd=3
[spi] spidev mode/bits/speed set (MODE3/8b/24MHz)
[spi] chardev request DC  @ /dev/gpiochip4 line 5 ...
[spi] chardev request RES @ /dev/gpiochip4 line 4 ...
[spi] chardev request CS  @ /dev/gpiochip5 line 1 ...
[spi] chardev-verify: DC=0(expect0) RES=1(expect1) CS=1(expect1)  ==> OK(chardev 真驱动了引脚)
[spi] spi_hal_init done
[tft] init: SLPOUT
[tft] init: SLPOUT +120ms ok
[tft] init: config cmds ok
[tft] init: DISPON
[tft] init: DISPON ok
[tft] init: clear-flush start
[tft] flush #1 start
[tft] flush #1 done
[tft] init: clear-flush done
[mq2] 初始化 MQ2（DO=GPIO0_1, AO=GPIO1_0/LSADC_CH0）...
[mq2] LSADC 寄存器已 mmap @ 0x120A0000 (CH0 走 /dev/mem 绕过驱动)
[mq2] @ DO=GPIO0_1(/dev/gpiochip0 line1) + AO=GPIO1_0/LSADC_CH0(/dev/mem 直读)
[mq2] 采集中，每 200ms 刷新，Ctrl+C 退出。
[mq2] DO=0 AO=2909 (71%)

3.2 TFT screen display

MQ gas sensor display effect

4 Troubleshooting

Problem	Possible cause	Solution
ALARM always shown	Threshold potentiometer set too low	Adjust the potentiometer on the module
Abnormal concentration value	AO read failure	Check the LSADC CH0 configuration
Sensor not responding	Insufficient power supply	Confirm the 5V supply