ESP8266 NodeMCU - DHT22 sensor and ThingSpeak

ESP8266 NodeMCU - DHT22 sensor and ThingSpeak

I have previously written about pushing temperature and humidity readings from an ESP8266 to a MQTT server using a DHT22 sensor. Later I leveraged NodeMCU’s built-in DHT22 library by using an online service to create a streamlined NodeMCU firmware fit for my needs. However, a reader asked me about pushing data to ThingSpeak.com instead and here is the reply.

Hardware

Follow my post here on how to connect all the parts.

NodeMCU firmware

Follow my post here on how to built a custom NodeMCU firmware and remember to check the DHT library. If you need help flashing the firmware you can take a look at my guide here.

Nodemcu-build.com default values and DHT selected

Software

Instead of the test code described in my post here, use the one below. Configure the following variables before uploading to the ESP8266:

  • thingspeak_channel_api_write_key
  • thingspeak_temperature_field_name
  • thingspeak_humidity_field_name
  • wifi_SSID
  • wifi_password

And I recommend to use a static IP address for faster connection times, just set the client_* variables.

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-- Thingspeak connect script with deep sleep
-- Remember to connect GPIO16 and RST to enable deep sleep
-- TODO: Log error codes to server

--############
--# Settings #
--############

--- Thingspeak ---
thingspeak_channel_api_write_key = "LU1TXYV15GBVTDHU"
thingspeak_temperature_field_name = "field1"
thingspeak_humidity_field_name = "field2"

--- WIFI ---
wifi_SSID = "wifi-Name"
wifi_password = "wifi-Password"
-- wifi.PHYMODE_B 802.11b, More range, Low Transfer rate, More current draw
-- wifi.PHYMODE_G 802.11g, Medium range, Medium transfer rate, Medium current draw
-- wifi.PHYMODE_N 802.11n, Least range, Fast transfer rate, Least current draw
wifi_signal_mode = wifi.PHYMODE_N
-- If the settings below are filled out then the module connects
-- using a static ip address which is faster than DHCP and
-- better for battery life. Blank "" will use DHCP.
-- My own tests show around 1-2 seconds with static ip
-- and 4+ seconds for DHCP
client_ip=""
client_netmask=""
client_gateway=""

--- INTERVAL ---
-- In milliseconds. Remember that the sensor reading,
-- reboot and wifi reconnect takes a few seconds
time_between_sensor_readings = 60000

--################
--# END settings #
--################

temperature = 0
humidity = 0

-- Connect to the wifi network
wifi.setmode(wifi.STATION)
wifi.setphymode(wifi_signal_mode)
wifi.sta.config(wifi_SSID, wifi_password)
wifi.sta.connect()
if client_ip ~= "" then
    wifi.sta.setip({ip=client_ip,netmask=client_netmask,gateway=client_gateway})
end

-- DHT22 sensor logic
function get_sensor_Data()
    dht=require("dht")
    status,temp,humi,temp_decimial,humi_decimial = dht.read(2)
        if( status == dht.OK ) then
            -- Prevent "0.-2 deg C" or "-2.-6"          
            temperature = temp.."."..(math.abs(temp_decimial)/100)
            humidity = humi.."."..(math.abs(humi_decimial)/100)
            -- If temp is zero and temp_decimal is negative, then add "-" to the temperature string
            if(temp == 0 and temp_decimial<0) then
                temperature = "-"..temperature
            end
            print("Temperature: "..temperature.." deg C")
            print("Humidity: "..humidity.."%")
        elseif( status == dht.ERROR_CHECKSUM ) then          
            print( "DHT Checksum error" )
            temperature=-1 --TEST
        elseif( status == dht.ERROR_TIMEOUT ) then
            print( "DHT Time out" )
            temperature=-2 --TEST
        end
    -- Release module
    dht=nil
    package.loaded["dht"]=nil
end

function loop()
    if wifi.sta.status() == 5 then
        -- Stop the loop
        tmr.stop(0)

        con = nil
        con = net.createConnection(net.TCP, 0)

        con:on("receive", function(con, payloadout)
            if (string.find(payloadout, "Status: 200 OK") ~= nil) then
                print("Posted OK to ThingSpeak");
            end
        end)

        con:on("connection", function(con, payloadout)

        -- Get sensor data
        get_sensor_Data()

        -- Post data to Thingspeak
        con:send(
            "POST /update?api_key=" .. thingspeak_channel_api_write_key ..
            "&field1=" .. temperature ..
            "&field2=" .. humidity ..
            " HTTP/1.1\r\n" ..
            "Host: api.thingspeak.com\r\n" ..
            "Connection: close\r\n" ..
            "Accept: */*\r\n" ..
            "User-Agent: Mozilla/4.0 (compatible; esp8266 Lua; Windows NT 5.1)\r\n" ..
            "\r\n")
        end)

        con:on("disconnection", function(con, payloadout)
            con:close();
            collectgarbage();
            print("Going to deep sleep for "..(time_between_sensor_readings/1000).." seconds")
            node.dsleep(time_between_sensor_readings*1000)
        end)

        -- Connect to Thingspeak
        con:connect(80,'api.thingspeak.com')
    else
        print("Connecting...")
    end
end

tmr.alarm(0, 100, 1, function() loop() end)

-- Watchdog loop, will force deep sleep the operation somehow takes too long
tmr.alarm(1,4000,1,function() node.dsleep(time_between_sensor_readings*1000) end)

Result

If everything went well you should see the following repeated every 60 seconds on your ESP8266:

0�~?�4�R���OCMa��_6E������

NodeMCU custom build by frightanic.com
	branch: dev
	commit: 093a895980fbd4ab8b3ebedcd6efe36e26419887
	SSL: true
	modules: node,file,gpio,wifi,net,tmr,adc,dht
 	built on: 2015-10-13 18:26
  powered by Lua 5.1.4
> Connecting...
Temperature: 23.2 deg C
Humidity: 39.1%
Posted OK to ThingSpeak
Going to deep sleep for 60 seconds

The results should now show up right away at your ThingSpeak channel.

Thingspeak with temperature and humidity data from and ESP8266 using a DHT22 sensor

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