Code for https://mrod.space/2020/11/14/diy-temp-sensor-nodemcu.html

init.lua

-- init.lua
------------

-- Altitude for calculating pressure
alt = 50 -- change this to your altitude in meters

-- Sensor Pins
sda, scl = 3, 4 -- leave these unless you're using different pins
print("Set up i2c...")
i2c.setup(0, sda, scl, i2c.SLOW)

print("Set up temp sensor...")
bme280.setup()

-- load params file if exists
if file.exists('eus_params.lua') then
    print("Load saved EUS params...")
    params = dofile('eus_params.lua')
end

-- https://stackoverflow.com/a/57299034  # Brian Tompsett, 7/13/2019
function round(number, precision)
   local fmtStr = string.format('%%0.%sf',precision)
   number = string.format(fmtStr,number)
   return number
end


-- if the params file exists, and has wifi creds, connect using them
if params and params.wifi_ssid and params.wifi_password then
    -- connect with cred ssaved in eus_params.lua
        wifi.setmode(wifi.STATION)
    print("Setting up wifi client...")
    station_cfg={}
    station_cfg.ssid=params.wifi_ssid
    station_cfg.pwd=params.wifi_password
    station_cfg.save=false -- we'll load it from this file, not flash
    wifi.sta.config(station_cfg)
    function callback()
        print('wifi status ' .. wifi.sta.status())
    end

    wifi.sta.connect(callback)
else
    -- start the EUS to get credentails
    print("Initializing (EUS)...")
    enduser_setup.start(
    function()
        print("EUS: Connected to wifi!")
    end,
    function(err, str)
        print("EUS: Err #" .. err .. ": " .. str)
    end
    )
end

-- every 30 seconds, run update_sensors() function to get new values 
update_timer = tmr.create():alarm( 30000, tmr.ALARM_AUTO, function() update_sensors() end )

-- data array that holds the current sensor values
data = {}

-- Webserver for retrieving sensor data. Runs on port 8080, returns the `data` object as JSON
srv = net.createServer(net.TCP, 30)
if srv then
    srv:listen(8080,
    function(conn)
        conn:on("receive",function(conn,payload)
            conn:send("HTTP/1.1 200 OK\n\n")
            if string.match(payload, "GET") then
                conn:send(sjson.encode(data))
            end
            if string.match(payload, "POST") then
                conn:send("Reseting...")
                file.remove("eus_params.lua")
            end
            conn:on("sent",function(conn) conn:close() end)
            conn = nil
        end)
    end)
end

-- reads from the BME280 and updates the `data` array
function update_sensors()
    local raw_data = {bme280.read(alt)}
    data["temp_c"] = round(raw_data[1]/100.0, 2)
    data["temp_f"] = round(((raw_data[1]/100.0) * 1.8) + 32, 2)
    data["pressure_mmhg"] = round(raw_data[2] * 0.000750061683, 2)
    data["humidity"] = round(raw_data[3]/1000.0, 2)
    state = wifi.sta.getip()
end


update_sensors()