NodeMCU with regular BMP280 readouts and webserver for JSON delivery

node_bmp280.lua

-- I assume that wifi is successfully initialized and that we have an IP already!

-- Init BMP280 sensor
altitude_measurement_location = 160
sda, scl = 6, 5
i2c.setup(0, sda, scl, i2c.SLOW)
mode = bme280.setup(nil, nil, nil, 0)
-- mode = 1 -> BMP280
-- mode = 2 -> BME280

-- Callback function to process sensor readings
bmp280_readings_available_event = function()
  T, P, H, QNH = bme280.read(altitude_measurement_location)
  Tsgn = (T < 0 and -1 or 1); T = Tsgn*T
  D = bme280.dewpoint(H, T)
  Dsgn = (D < 0 and -1 or 1); D = Dsgn*D
  print("New sensor readout available, check variables: T, P, H, QNH, D")
  print("For a neat JSON object with current values do a GET request on {node_IP}:80/")
end

-- Do an initial readout to have some values in case someone requests them
bme280.startreadout(0, bmp280_readings_available_event)

-- Create timer to read BMP280 every 30 seconds
bmp280timer = tmr.create()
bmp280timer:register(30000, tmr.ALARM_AUTO, function()
  -- Read current values from sensor
  bme280.startreadout(0, bmp280_readings_available_event)
end)
bmp280timer:start()

-- Start a simple webserver to serve the values in a neat JSON object
srv=net.createServer(net.TCP)
srv:listen(80,function(conn)
  conn:on("receive", function(sck,request)
    local json = "{";
    json = json.."\"nodeid\": "..node.chipid()..", ";
    json = json.."\"sensors\": {";
    json = json.."\"bmp280\": {";
    json = json.."\"temperatur\": "..string.format("%s%d.%02d", Tsgn<0 and "-" or "", T/100, T%100)..", ";
    json = json.."\"pressure\": "..string.format("%d.%03d", P/1000, P%1000)..", ";
    json = json.."\"pressure_sea\": "..string.format("%d.%03d", QNH/1000, QNH%1000)..", ";
    json = json.."\"humidity\": "..string.format("%d.%03d", H/1000, H%1000)..", ";
    json = json.."\"dew_point\": "..string.format("%s%d.%02d", Dsgn<0 and "-" or "", D/100, D%100);
    json = json.."}";
    json = json.."}";
    json = json.."}";
    sck:send("HTTP/1.0 200 OK\r\nContent-Type: application/json\r\n\r\n");
    sck:send(json);
    collectgarbage();
  end)
  conn:on("sent", function(sck) sck:close() end)
end)