# ESP8266 Lua/NodeMCU module for MH-Z19 CO₂ sensor

This repository contains a Lua module (`mh-z19.lua`) as well as ESP8266/NodeMCU
MQTT gateway application example (`init.lua`) for the **MH-Z19** carbon dioxide
(CO₂) sensor.

## Dependencies

mh-z19.lua has been tested with Lua 5.1 on NodeMCU firmware 3.0.1
(Release 202112300746, integer build). It requires the following modules.

* struct

Most practical applications (such as the example in init.lua) also need the
following modules.

* gpio
* mqtt
* node
* softuart
* tmr
* uart
* wifi

## Setup

Connect the MH-Z19 sensor to your ESP8266/NodeMCU board as follows.

* MH-Z19 GND (black wire) → ESP8266/NodeMCU GND
* MH-Z19 Vin (red wire) → ESP8266/NodeMCU 5V
* MH-Z19 Rx (blue wire) → NodeMCU D1 (ESP8266 GPIO5)
* MH-Z19 Tx (green wire) → NodeMCU D2 (ESP8266 GPIO4)

If you use different pins for TXD and RXD, you need to adjust the
softuart.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 MH-Z19 connection.

## Usage

Copy **mh-z19.lua** to your NodeMCU board and set it up as follows.

```lua
mh_z19 = require("mh-z19")
port = softuart.setup(9600, 1, 2)
port:on("data", 9, uart_callback)

function uart_callback(data)
	if mh_z19.parse_frame(data) then
		-- mh_z19.co2 contains the CO₂ concentration in ppm
	end
end

port:write(mhz19.c_query)
```

## 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 = "..."
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 stored as `mh_z19,[influx_attr] co2_ppm=...`