Document setup and application example

# ESP8266 Lua/NodeMCU module for Sensirion SCD40/SCD41 CO₂ sensor

# ESP8266 Lua/NodeMCU module for Sensirion SCD4x CO₂ sensors

This repository contains an ESP8266 NodeMCU Lua module (`scd4x.lua`) as well as

MQTT / HomeAssistant / InfluxDB integration example (`init.lua`) for

**Sensirion SCD40/SCD41** CO₂ sensors.

**Sensirion SCD4x** CO₂ sensors connected via I²C.

## Dependencies

* mqtt

* node

* tmr

* uart

* wifi

## Setup

Connect the SCD4x sensor to your ESP8266/NodeMCU board as follows.

* SCD4x GND → ESP8266/NodeMCU GND

* SCD4x 3V3 → ESP8266/NodeMCU 3V3

* SCD4x SCL → NodeMCU D1 (ESP8266 GPIO4)

* SCD4x SDA → NodeMCU D2 (ESP8266 GPIO5)

SDA and SCL must have external pull-up resistors to 3V3.

If you use different pins for SDA and SCL, you need to adjust the

i2c.setup call in the examples provided in this repository to reflect

those changes. Keep in mind that some ESP8266 pins must have well-defined logic

levels at boot time and may therefore be unsuitable for SCD4x connection.

## Usage

Copy **scd4x.lua** to your NodeMCU board and set it up as follows.

```lua

scd4x = require("scd4x")

i2c.setup(0, sda_pin, scl_pin, i2c.SLOW)

i2c.setup(0, 2, 1, i2c.SLOW)

scd4x.start()

-- can be called with up to 1 Hz

function some_timer_callback()

	local co2, raw_temp, raw_humi = scd4x.read()

	if co2 == nil then

		print("SCD4x error")

	if co2 ~= nil then

		-- co2      : CO₂ concentration [ppm]

		-- raw_temp : raw_temp/2¹⁶ - 45 == Temperature [°c]

		-- raw_humi : raw_humi/2¹⁶ == Humidity [%]

	else

		-- CO₂[ppm] == co2, Temperature[°c] == raw_temp/2¹⁶ - 45, Humidity[%] == raw_humi/2¹⁶

		print("SCD4x error")

	end

end

```

See **init.lua** for an example. To use it, you need to create a **config.lua** file with WiFI and MQTT settings:

## Application Example

**init.lua** is an example application with HomeAssistant integration.

To use it, you need to create a **config.lua** file with WiFI and MQTT settings:

```lua

station_cfg.ssid = "..."

station_cfg.pwd = "..."

station_cfg = {ssid = "...", pwd = "..."}

mqtt_host = "..."

```

Optionally, it can also publish readings to an InfluxDB.

To do so, configure URL and attribute:

```lua

influx_url = "..."

influx_attr = "..."

```

Readings will be published as `scd4x[influx_attr] co2_ppm=%d,temperature_degc=%d.%d,humidity_relpercent=%d.%d`.

So, unless `influx_attr = ''`, it must start with a comma, e.g. `influx_attr = ',device=' .. device_id`.

station_cfg = {}

publishing_mqtt = false

publishing_http = false

dofile("config.lua")

print("ESP8266 " .. chip_id)

print("SCD4x " .. chip_id)

ledpin = 4

gpio.mode(ledpin, gpio.OUTPUT)