Hardware

The device is an ESP32 LOLIN32 with four sensors and a display. This page lists what is in the bill of materials and how it is wired. Each peripheral has its own chapter further down.

Bill of materials

Part	Interface	Chapter
ESP32 LOLIN32 board	:	ESP32 & pin configuration
MQ-2 gas sensor module	Analog out → GPIO 32	MQ-2 sensing
DHT22 temperature and humidity sensor	1-Wire → GPIO 13	DHT22 climate monitoring
PIR motion sensor	Digital out → GPIO 34	PIR sensing and wakeup
16x2 I2C LCD with PCF8574 backpack	I2C → GPIO 17 / 19	LCD interface
3.7 V LiPo battery with charging circuit	Power → VIN	Low-power architecture

Pin map

Every pin is defined as a macro in include/config.h.

Macro	Pin	Signal
`PIN_GAS_SENSOR`	GPIO 32	MQ-2 analog output (ADC1_CH4)
`PIN_TEMP_HUM_SENSOR`	GPIO 13	DHT22 data line
`PIN_MOTION_SENSOR`	GPIO 34	PIR output, also the deep-sleep wake source
LCD SDA	GPIO 17	I2C data
LCD SCL	GPIO 19	I2C clock
Status LED	GPIO 22	digital output

GPIO 34 is input-only and has no internal pull-up, which is why the PIR is powered from the board’s 5 V rail and its output is read directly.

Wiring

3.3V  ──> MQ-2 VCC, DHT22 VCC, LCD VCC
GND   ──> common ground for every module
VIN   ──> battery positive (through a regulator if the cell needs one)
5V    ──> PIR VCC, soldered on the board

MQ-2 A0  ──> GPIO 32
DHT22    ──> GPIO 13
PIR OUT  ──> GPIO 34
LCD SDA  ──> GPIO 17
LCD SCL  ──> GPIO 19

Power

The device is battery operated. It spends nearly all of its time in deep sleep, wakes on motion, reads the sensors, updates the display and sleeps again. The LCD backlight is switched off while the device sleeps. See Low-power architecture for the wake timing and the 20 second idle window.