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+# ESP8266 Lua/NodeMCU module for MAX44009 illuminance sensor
+
+This repository contains an ESP8266 NodeMCU Lua module (`max44009.lua`) as well
+as MQTT / HomeAssistant / InfluxDB integration example (`init.lua`) for
+**MAX44009** illuminance sensors.
+
+## Dependencies
+
+max44009.lua has been tested with Lua 5.1 on NodeMCU firmware 3.0.1 (Release
+202112300746, float build). It requires the following modules.
+
+* bit
+* i2c
+
+Most practical applications (such as the example in init.lua) also need the
+following modules.
+
+* gpio
+* mqtt
+* node
+* tmr
+* wifi
+
+## Setup
+
+Connect the MAX44009 sensor to your ESP8266/NodeMCU board as follows.
+
+* MAX44009 GND → ESP8266/NodeMCU GND
+* MAX44009 VCC → ESP8266/NodeMCU 3V3
+* MAX44009 SDA → NodeMCU D1 (ESP8266 GPIO5)
+* MAX44009 SCL → NodeMCU D2 (ESP8266 GPIO4)
+
+If you use different pins for SCL and SDA, 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 MAX44009 connection.
+
+## Usage
+
+Copy **max44009.lua** to your NodeMCU board and set it up as follows.
+
+```lua
+max44009 = require("max44009")
+i2c.setup(0, sda_pin, scl_pin, i2c.SLOW)
+
+-- can be called with up to 1 Hz
+function some_timer_callback()
+	local lx = max44009.read()
+	if lx == nil then
+		print("MAX44009 error")
+	else
+		-- lx contains the illuminance. Note that it is a floating point value.
+	end
+end
+```
+
+## 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 = "foo", pwd = "bar"}
+mqtt_host = "..."
+```
+
+Optionally, it can also publish readings to InfluxDB.
+To do so, configure URL and attribute:
+
+```lua
+influx_url = "..."
+influx_attr = "..."
+```
+
+Readings will be stored as `max44009[influx_attr] illuminance_lx=...`.
+So, unless `influx_attr = ''`, it must start with a comma, e.g. `influx_attr = ',device=' .. device_id`.