initial commit

config.lua

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

This repository contains a Lua module (`scd4x.lua`) as well as

MQTT-based HomeAssistant integration (`init.lua`) for **Sensirion SCD40/SCD41**

CO₂ sensors.

## Dependencies

scd4x.lua has been tested with Lua 5.1 on NodeMCU firmware 3.0.1 (Release

202112300746, integer build). It requires the following modules.

* i2c

The MQTT HomeAssistant integration in init.lua additionally needs the following

modules.

* gpio

* mqtt

* node

* tmr

* uart

* wifi

## 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)

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")

	else

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

	end

end

```

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

```lua

station_cfg.ssid = "..."

station_cfg.pwd = "..."

mqtt_host = "..."

```

station_cfg = {}

dofile("config.lua")

delayed_restart = tmr.create()

push_timer = tmr.create()

chip_id = node.chipid()

device_id = "esp8266_" .. chip_id

mqtt_prefix = "sensor/" .. device_id

mqttclient = mqtt.Client(device_id, 120)

print("ESP8266 " .. chip_id)

ledpin = 4

gpio.mode(ledpin, gpio.OUTPUT)

gpio.write(ledpin, 0)

scd4x = require("scd4x")

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

function log_restart()

	print("Network error " .. wifi.sta.status() .. ". Restarting in 20 seconds.")

	delayed_restart:start()

end

function setup_client()

	print("Connected")

	gpio.write(ledpin, 1)

	if not scd4x.start() then

		print("SCD4x initialization error")

	end

	publishing = true

	mqttclient:publish(mqtt_prefix .. "/state", "online", 0, 1, function(client)

		publishing = false

		push_data()

	end)

end

function connect_mqtt()

	print("IP address: " .. wifi.sta.getip())

	print("Connecting to MQTT " .. mqtt_host)

	delayed_restart:stop()

	mqttclient:on("connect", hass_register)

	mqttclient:on("offline", log_restart)

	mqttclient:lwt(mqtt_prefix .. "/state", "offline", 0, 1)

	mqttclient:connect(mqtt_host)

end

function connect_wifi()

	print("WiFi MAC: " .. wifi.sta.getmac())

	print("Connecting to ESSID " .. station_cfg.ssid)

	wifi.eventmon.register(wifi.eventmon.STA_GOT_IP, connect_mqtt)

	wifi.eventmon.register(wifi.eventmon.STA_DHCP_TIMEOUT, log_restart)

	wifi.eventmon.register(wifi.eventmon.STA_DISCONNECTED, log_restart)

	wifi.setmode(wifi.STATION)

	wifi.sta.config(station_cfg)

	wifi.sta.connect()

end

function push_data()

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

	if co2 == nil then

		print("SCD4x error")

	else

		local json_str = string.format('{"co2_ppm": %d, "temperature_degc": %d.%d, "humidity_relpercent": %d.%d, "rssi_dbm": %d}', co2, raw_temp/65536 - 45, (raw_temp%65536)/6554, raw_humi/65536, (raw_humi%65536)/6554, wifi.sta.getrssi())

		if not publishing then

			publishing = true

			gpio.write(ledpin, 0)

			mqttclient:publish(mqtt_prefix .. "/data", json_str, 0, 0, function(client)

				publishing = false

				gpio.write(ledpin, 1)

				collectgarbage()

			end)

		end

	end

	push_timer:start()

end

function hass_register()

	local hass_device = string.format('{"connections":[["mac","%s"]],"identifiers":["%s"],"model":"ESP8266","name":"ESP8266 with SCD4x","manufacturer":"DIY"}', wifi.sta.getmac(), device_id)

	local hass_entity_base = string.format('"device":%s,"state_topic":"%s/data","expire_after":600', hass_device, mqtt_prefix)

	local hass_co2 = string.format('{%s,"name":"CO₂","object_id":"%s_co2","unique_id":"%s_co2","device_class":"carbon_dioxide","unit_of_measurement":"ppm","value_template":"{{value_json.co2_ppm}}"}', hass_entity_base, device_id, device_id)

	local hass_temp = string.format('{%s,"name":"Temperature","object_id":"%s_temperature","unique_id":"%s_temperature","device_class":"temperature","unit_of_measurement":"°c","value_template":"{{value_json.temperature_degc}}"}', hass_entity_base, device_id, device_id)

	local hass_humi = string.format('{%s,"name":"Humidity","object_id":"%s_humidity","unique_id":"%s_humidity","device_class":"humidity","unit_of_measurement":"%%","value_template":"{{value_json.humidity_relpercent}}"}', hass_entity_base, device_id, device_id)

	local hass_rssi = string.format('{%s,"name":"RSSI","object_id":"%s_rssi","unique_id":"%s_rssi","device_class":"signal_strength","unit_of_measurement":"dBm","value_template":"{{value_json.rssi_dbm}}","entity_category":"diagnostic"}', hass_entity_base, device_id, device_id)

	mqttclient:publish("homeassistant/sensor/" .. device_id .. "/co2/config", hass_co2, 0, 1, function(client)

		mqttclient:publish("homeassistant/sensor/" .. device_id .. "/temperature/config", hass_temp, 0, 1, function(client)

			mqttclient:publish("homeassistant/sensor/" .. device_id .. "/humidity/config", hass_humi, 0, 1, function(client)

				mqttclient:publish("homeassistant/sensor/" .. device_id .. "/rssi/config", hass_rssi, 0, 1, function(client)

					collectgarbage()

					setup_client()

				end)

			end)

		end)

	end)

end

delayed_restart:register(20 * 1000, tmr.ALARM_SINGLE, node.restart)

push_timer:register(20 * 1000, tmr.ALARM_SEMI, push_data)

connect_wifi()

local scd4x = {}

local device_address = 0x62

scd4x.bus_id = 0

function scd4x.start()

	i2c.start(scd4x.bus_id)

	if not i2c.address(scd4x.bus_id, device_address, i2c.TRANSMITTER) then

		return false

	end

	i2c.write(scd4x.bus_id, {0x21, 0xb1})

	i2c.stop(scd4x.bus_id)

	return true

end

function scd4x.stop()

	i2c.start(scd4x.bus_id)

	if not i2c.address(scd4x.bus_id, device_address, i2c.TRANSMITTER) then

		return false

	end

	i2c.write(scd4x.bus_id, {0x3f, 0x86})

	i2c.stop(scd4x.bus_id)

	return true

end

function scd4x.read()

	i2c.start(scd4x.bus_id)

	if not i2c.address(scd4x.bus_id, device_address, i2c.TRANSMITTER) then

		return nil

	end

	i2c.write(scd4x.bus_id, {0xec, 0x05})

	i2c.stop(scd4x.bus_id)

	i2c.start(scd4x.bus_id)

	if not i2c.address(scd4x.bus_id, device_address, i2c.RECEIVER) then

		return nil

	end

	local data = i2c.read(scd4x.bus_id, 9)

	i2c.stop(scd4x.bus_id)

	local co2 = string.byte(data, 1) * 256 + string.byte(data, 2)

	local temp_raw = 175 * (string.byte(data, 4) * 256 + string.byte(data, 5))

	local humi_raw = 100 * (string.byte(data, 7) * 256 + string.byte(data, 8))

	return co2, temp_raw, humi_raw

end

return scd4x