NodeMCU Examples

This page shows you some nodeMCU examples in the lua scripting language. this language is fairly different to the Arduino C/C++ but the great advantage is that you can update individual code sections without re-flashing the whole lot.

It means you don't wait 60 seconds to update the device, instead it is a matter of seconds. This is the great advantage of scripting languages - development time is vastly reduced.

You will need to update your nodeMCU V3 (ESP8266 based) if you have used the Arduino IDE method (or it has old firmware installed) as the nodeMCU firmware will have been overwritten. It's not a problem - instructions for re-fashing nodeMCU firmware are here.

If you have not installed or used ESPlorer you will need to Install ESPlorer to follow along with the examples here.

ESP8266 based lolin nodeMCU breakout board

NodeMCU Examples tutorial

How to access pins using lua

The following example shows you how to access pins on an ESP module with commands that are similar to Arduino C code uploading them with ESPlorer. These commands have been tested on a Lolin nodeMCU V3 board.

Warning: In lua the pin information is different to Arduino. The pin number refers to the label on the board i.e. D4 is pin 4.

Note: Pin 4 is attached to the built in LED and this is pulled high so sending a zero turns it on. This was found by trial and error.

-- NodeMCU Examples
pin = 4
gpio.mode(pin,gpio.OUTPUT)
gpio.write(pin,gpio.LOW)
print(gpio.read(pin))

Save the above as file:led_on.lua

Instructions for uploading lua files

You can find out how to upload the lua programs using ESPlorer here.

LED Flash

Flashing the Built in LED with Lua

Here's a program to flash the built in LED. This is the way you would initially think of writing the code in C - non event driven. Even though it works don't use this in general. You need to think in terms of releasing processing time and not making loops that do not exit (See next example for event driven timer programming).

-- NodeMCU Examples
LEDpin = 4         -- Declare LED pin no.
delayuS = 500000   -- Set delay in microSecond. here 0.5 second

gpio.mode(LEDpin,gpio.OUTPUT)-- Set LED pin as GPIO output pin

while(1)           -- Define infinite while loop
do
   gpio.write(LEDpin,gpio.HIGH)-- Set LED pin HIGH i.e. LED OFF
   tmr.delay(delayuS)  -- timer Delay
   gpio.write(LEDpin,gpio.LOW)-- Set LED pin LOW i.e. LED ON
   tmr.delay(delayuS)  -- timer Delay  
   tmr.wdclr() -- Stop watchdog resetting the MCU
end

Save the above as file: led_flash1.lua

Note that the tmr.wdclr() function is used to stop the watchdog reset which is needed it in this function to stop a reset because it is not event driven - See next example for event driven blink.

Event driven lua LED blink : NodeMCU Examples

The previous code example does not use event driven programming so lets write it the way lua should be used using a timer to create an event that will trigger led blink.

Note the lua script below operates for newer lua SDK > 2.1.0. -timer operation.

-- NodeMCU Examples
-- Event driven programming
delayms = 400
LEDpin = 4
LEDstate = 0

gpio.mode(LEDpin,gpio.OUTPUT)

function tog()
   if (LEDstate) then gpio.write(LEDpin,gpio.LOW)  print(0)
                 else gpio.write(LEDpin,gpio.HIGH) print(1)
   end
   LEDstate = not LEDstate
end

-- oo calling method
local mytimer = tmr.create()
mytimer:register(delayms, tmr.ALARM_AUTO, function () tog() end)
mytimer:start()

Save the above as File: led_flash2.lua

The event driver (the timer) is at the end of the code.

First a timer object is created 'mytimer'. Then the timer is registered with the delay time, the type of repeat - ALARM_AUTO means repeat this timer event forever.

Next is the function tog that is called when the timer triggers. Then the timer is started. You can use 'mytimer:alarm' instead of register and start, which both registers and starts the timer if you want.

So in this code the timer repeatedly calls function tog() at the delayms rate which is set to 400ms.

Find Access Points

Finding Visible Networks or Access Points

This script lets you see local network names (ssid) and other related information. It also shows the signal strength of any local network, which can be useful to check whether you have got a dead zone nearby in your own Wifi setup.

-- NodeMCU Examples
-- Get Access Point data
station_cfg={ssid="SSID",pwd="password"}
station_cfg.save=true
wifi.sta.config(station_cfg)

-- https://github.com/nodemcu/nodemcu-firmware/blob/master/docs/en/modules/wifi.md
-- Print AP list that is easier to read
function listap(t) -- (SSID : Authmode, RSSI, BSSID, Channel)
    print("\n"..string.rep(" ",32-4).."SSID\t\t\t\t  BSSID\t  RSSI\t\tAUTHMODE\tCHANNEL")
    for bssid,v in pairs(t) do
        local ssid, rssi, authmode, channel = string.match(v, "([^,]+),([^,]+),([^,]+),([^,]*)")
        print(string.format("%32s",ssid).."\t"..bssid.."\t  "..rssi.."\t\t"..authmode.."\t\t\t"..channel)
    end
    print("---------")
    for bssid,v in pairs(t) do
    print(bssid,v)
    end
end

wifi.sta.getap(1,listap)

Save the file as wifi_getap.lua.

The data returned from the getap() function is a table that has 2 columns of data. This is the raw data with BSSI on the left and all the other data on the right:

40:0d:10:42:9f:09	VM9253421,-87,4,1
52:0d:10:42:9f:09	Virgin Media,-86,5,1
78:3e:53:ab:ca:96	SKY7C621,-88,3,6
24:a7:dc:50:5a:a2	SKY6F103,-92,3,1
00:13:f7:ca:01:bb	SMC,-90,1,3
0c:f9:c0:4d:d9:66	SKY1BE56,-92,3,6
cc:2d:21:0b:bd:81	NOVA_BD78,-92,4,6
84:1b:5e:a5:69:82	virginmedia3134410,-96,4,6
50:6a:03:1e:61:68	VM989231-2G,-89,4,6
8a:30:d9:61:27:76	BTWifi-with-FON,-85,0,1
24:a7:dc:6b:45:e2	SKY7C621,-88,3,6
84:1b:5e:a7:cf:62	virginmedia1684506,-89,4,11
d2:05:c2:3a:8f:01	Virgin Media,-91,5,1
38:a6:ce:5e:98:de	SKY6F103,-86,3,11
bc:30:d9:61:27:75	BTHub6-2MX3,-84,3,1
cc:2d:21:0b:bd:89	NOVA_BD78,-92,4,6
52:0d:10:df:bd:99	VM-guest3451593,-91,4,1

Explanation of lua string match

One of the interesting things about lua is that functions can return multiple values. The following string match returns all the regular expression matches, placing them sequentially into variables ssid, rssi, authmode, channel.

local ssid, rssi, authmode, channel = string.match(v, "([^,]+),([^,]+),([^,]+),([^,]*)")

This means you can write very compact code but you will need to understand regexp (if possible!).

This tool is a useful way of testing regexp expressions: http://myregexp.com/

The Caret '^' means NOT in this case so the characters to be found are [^,]+ anything that is not a comma. The plus means at least one match must be found.

Adding parenthesis and a trailing comma ([^,]+), means the next character must be a comma. The parenthesis tell the function to return the contents as a matching string.

So the first match finds the first element on the right column of data (and ignores the comma) i.e. the ssid. The next match is the same, and finds the signal strength, and the next match is also the same, finding the authmode.

The last match ([^,]*) . * means grab any or zero matches. Since there is no comma ^, it matches the rest of the remaining characters assigning them to channel.

Simple Webserver

A Simple Webpage Server using ESPlorer

Set SSID and PASSWORD to your WiFi name and password.

-- NodeMCU Examples
-- Simple Web page server

wifi.setmode(wifi.STATION)
station_cfg={ssid="SSID",pwd="password"}
station_cfg.save=true
wifi.sta.config(station_cfg)

srv=net.createServer(net.TCP)
srv:listen(80,function(conn)
   conn:on("receive",function(conn,payload)
      print(payload)
      conn:send("<h1>This is a simple webserver</h1>")
      conn:send("<h2>Hello</h2>")
      conn:send("Hello, Lolin NodeMCU V3.")
   end)
end)

Save the above text as simple_webserver.lua.

Now go to your router and find out the IP address assigned to the ESP module (or use some more lua code shown as another example below to do this) and then go to a browser and type that IP into the URL bar and you should see something like this (the IP address will be different for your system):

Served as a webpage.

Note: To stop the webserver as a program instruction rather than a hard reset use the lua code:

net.server:close()

Webserving the page from nodeMCU reset

To make the nodeMCU serve the page from reset you need to put the function into init.lua however if you put the existing file into init.lua you won't be able to flash it with a different program - the file will immediately execute and you won't be able to re-program the ESP module from the ESPLorer interface. Instead you would have to re-flash the chip with the original firmware.

To get round this you need to delay the start of the function execution. This is done by using a timer that delays for 6 seconds before starting. This gives you time to send the command tmr.stop() so it never gets to the execute the function. you can find a convenient button for this in the command tab in ESPlorer.

The timer command required is:

print("About to start a simple webserver in 10 seconds")
tmr.alarm(0,6000,0,function() dofile("simple_webserver.lua") end)

So save the above code as init.lua

Note: You can also see in the terminal window the data requests from the Browser i.e. when you refresh the Browser page (or as it automatically refreshes on keep alive mode).

Now press the rest button on the ESP module and refresh the browser - page will not be found. wait >10 secs and refresh to see the page. It will also refresh when the ESP module wakes up anyway as it is in keep-alive mode.

Now try getting back control of the ESP module - by resetting and the issuing the command tmr.stop()

You can probably see that you could read a button input and change the output data sent to a served page using gpio.read(pin) and taking action on the result. This would be the basis of making a webpage indicate data from the ESP module e.g. from a sensor or a button press etc.

Stopping init.lua

The other way to stop the action of init.lua is to remove the file using the command:

file.remove("init.lua")

Webserver Start Count Down

This script does the same job as the last one except that it shows you how long you have until the webserver starts. A countdown is output to the serial monitor.

-- NodeMCU Examples
-- Countdown to webserver start

print("\nAbout to start a simple webserver in 10 seconds")

count = 6
print("\n")
function show_count()
   count = count - 1
   if (count<=0) then
      countdown:unregister()
      dofile("simple_webserver.lua")
      print("Starting Server");
   else
      buf = tostring(count).. " seconds to webserver start"
      print(buf)
   end
end

countdown = tmr.create()
countdown:alarm(1000, tmr.ALARM_AUTO, function() show_count() end)

Save the above file as init.lua overwriting the previous file.

Find out the nodeMCU IP Address

Find IP address (New style nodeMCU library)

The following lua script runs the previous webserver script to start a connection. It the waits until an IP address is found and prints it out. Note how the timer object is using an object oriented method to create it and unregister it.

There are 7 timers in the ESP8266 nodeMCU implementation numbered 0 to 6. In the old code above you have to choose which number to use - that means you had to keep track of the numbers and could lead to assignment errors.

In the new code below there are no numbers - the next timer just gets assigned. Also these seem to be software timers so there are more than 7. Try creating more than 7 timer objects and see.

-- NodeMCU Examples
-- Find assigned IP address.
--
-- A timer is initiated to regularly check if the ip
-- has changed from nil - if it has then the
-- ip address is displayed and the timer is stopped
-- and freed for other use.
--
-- oo timer method

dofile("simple_webserver.lua")

local ipTimer = tmr.create()
ipTimer:alarm(1000, 1, function() check()  end) 

function check()
if wifi.sta.getip() == nil then
      print("Connecting to AP...")
   else
      print("IP: ",wifi.sta.getip())
      ipTimer:unregister()
   end
end

Save the file as find_ap.lua

This the typical output (yours will be different)

> Connecting to AP...
Connecting to AP...
Connecting to AP...
Connecting to AP...
Connecting to AP...
Connecting to AP...
IP: 	192.168.0.19	255.255.255.0	192.168.0.1

The left value is the assigned IP, followed by the netmask, and gateway IP.

Control Outputs Using ESP module>>>

<<< Back to Installing ESPlorer

Top of page

NodeMCU Examples

NodeMCU Examples tutorial
   How to access pins using lua

Instructions for uploading lua files

LED Flash
   Flashing the Built in LED with Lua
   Event driven lua LED blink

Find Access Points
   Finding Visible Networks or Access Points
   Explanation of lua string match

Simple Webserver
   A Simple Webpage Server using ESPlorer
   Webserving the page from nodeMCU reset
   Stopping initlua
   Webserver Start Count Down

Find out the nodeMCU IP Address
   Find IP address New style nodeMCU library

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