ESP8266 Community Forum

- Mon Mar 21, 2016 11:06 am #43716 I'm trying to read the temperature and humidity from a DHT22 sensor with the ESP8266-12. So far I tried many different versions of the firmware (with DHT compiled into the firmware and with the dht22.lua included in script).
Current firmware: http://nodemcu-build.com/ default settings + DHT

It all results in the same. Humidity is either 1 or nill. When I breath at the sensor, I get some results between 30 en 99. Time between measurement is at least 3 seconds since it can become a problem.

Can someone take a look at the connections / code below. Anything I can try to make it work?


Connections:

ESP8266-12:
VCC ----> 3.3V of power supply
GND ----> Ground of power supply
CH_PD ----> HIGH (3.3V)
GPIO2 ----> HIGH (3.3V)
GPIO15 ----> LOW (GND)
GPIO0 ----> HIGH (3.3V)
GPIO16 ----> RST

DHT22
PIN1: --> 3.3V of power supply
PIN2: --> GPIO12 of ESP8266-12
PIN4: --> Ground of power supply


Code:

init.lua

Code: Select allfunction startup()
    if abort == true then
        print('startup aborted...')
        return
        end
    print('starting user.lua...')
    dofile('user.lua')
    end

abort = false
print("1 seconds to abort user.lua...")
tmr.alarm(0,1000,0,startup)


user.lua

Code: Select all--- WiFi Connect
wifi.setmode(wifi.STATION)
wifi.sta.config("ssid","password")
tmr.alarm(1, 1000, 1, function()
    if wifi.sta.getip()== nil then
        print("IP unavaiable, Waiting...")
    else
        tmr.stop(1)
        print("ESP8266 mode is: " .. wifi.getmode())
        print("Connected...")
        print("MAC: " .. wifi.ap.getmac())
        print("IP :".. wifi.sta.getip())

        -- Read sensor and post data

        -- Read DHT22 Sensor on GPIO12 (pin 6)
        status, temp, humi, temp_dec, humi_dec = dht.read(6)
        --todo: add some errorchecking for dht.read

        -- Post data
        print("Sending data:"..temp.." "..humi..".")
        conn=net.createConnection(net.TCP, 0)
        conn:on("receive", function(conn, payload) print(payload) end )
        conn:on("connection", function(c)
            conn:send("GET /update?api_key=notsosupersecretkey="..temp.."&field2="..humi..""
            .. " 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)
        conn:connect(80,"54.88.155.198")

        tmr.alarm(2, 1000, 1, function()
            if conn == nil then -- is this the right way to make the program wait before deepsleep?
                print("Still sending data, please wait...")
            else
                tmr.stop(2)
                print("Going to sleep for 55secs...")
                node.dsleep(55000000)
            end
        end)
    end
end)


- Mon Mar 21, 2016 5:32 pm #43743 I think that you will find that this is a hardware issue rather than a firmware one. Make sure that your have the right pull-ups etc.

Please see my Developer FAQ for Q&A on nodeMCU Lua before asking a question here that's already been answered. This and the other official documentation should be your first reference for developing Lua Apps

- Wed Mar 23, 2016 7:32 am #43867 Thought that too ...
Already tried all kinds of pullup resistor values, but they all gave the same result.

- Mon Mar 28, 2016 3:40 pm #44204 with my dht22, I have a 4.7k resistor between +3.3 and pin2.

I read the sensor with the following function which is identical to yours:

Code: Select allfunction readDHT(pin)   
   status,tempdht,humidht,temp_decimal,humi_decimal = dht.read(pin)
   if( status == dht.ERROR_CHECKSUM or status == dht.ERROR_TIMEOUT  ) then
        tempdht = nil
        humidht = nil
     end   
     return tempdht,humidht
end