As it was requested from you, my readers, in Part 3  of our CBDB saga, we will start building a simple, high precision, Temperature Data logger based on the MCP9808 chip, a ±0.5°C Maximum Accuracy Digital Temperature Sensor. As far as I know this is the first time NodeMCU float version I2C Driver for MCP9808.


     • Accuracy:
        – ±0.25 (typical) from -40°C to +125°C
       – ±0.5°C (maximum) from -20°C to 100°C
       – ±1°C (maximum) from -40°C to +125°C
  • User-Selectable Measurement Resolution:
       – +0.5°C, +0.25°C, +0.125°C, +0.0625°C
  • User-Programmable Temperature Limits:
       – Temperature Window Limit
       – Critical Temperature Limit
   • User-Programmable Temperature Alert Output
    • Operating Voltage Range: 2.7V to 5.5V
    • Operating Current: 200 μA (typical)
    • Shutdown Current: 0.1 μA (typical)
   • 2-wire Interface: I2C/SMBus Compatible
    • Available Packages: 2×3 DFN-8, MSOP-8

For more details, please see MCP9008 Datasheet

Don’t be scared by the MSOP-8 package, with a small MSOP to DIP adapter will fit great in our CBDB extension slots it will not matter at all.

MSSOP8-DIP8 package adapter

What we will need:

  • CBDB Board
  • USB adapter (take a look on Part 1 for details how to connect them together)
  • MCP9808 Module from above
  • LED module (if you want maybe a LED ticker)


CBDB with MCP9808 Temperture module
CBDB with MCP9808 Temperature module + LED ticker

For programming and uploading the driver and the software we will continue to use the LuaUploader as before.

Driver implementation.

As MCP9808 has a I2C compatible compatible interface, building a driver for it it’s a pretty straigh forward process:

1. Init I2C bus/interface

          dev_addr = 0x1F,
          init = function (self, sda, scl)
          = 0
           i2c.setup(, sda, scl, i2c.SLOW)

2. Read / Write to/from the desired register location.

  •  READ Register function
     read_reg = function(self, dev_addr, reg_addr)
          i2c.address(, dev_addr ,i2c.TRANSMITTER)
          i2c.address(, dev_addr,i2c.RECEIVER)
          return c
  • READ Temperature function
    readTemp = function(self)
            h, l = string.byte(self:read_reg(0x1F, 0x05), 1, 2)
            --check if Ta > 0C or Ta<0C
            Sgn =,0x10)              
            -- transform - CLEAR Sing BIT if Ta < 0C
            h2 =,0x0F)
            tp = h2*16+l/16
            --END calculate temperature for Ta > 0
           return tp

NOTE: This is for Tambient > 0°C only. Take a look in the  MCP9008 Datasheet . If you need it also on the negative temperature scale then you need to do some extra transformations as the temperature data is stored in the 16-bit read-only Ambient Temperature register Ta as 13-bit data in two’s complement format.

For testing, just save the code on ESP as ‘mcp9808.lua‘, restart ESP and run:

           require('mcp9808')                 --call for new created MCP9808 Module Driver
           sda=2 --GPIO4                      --  declare your I2C interface PIN's
           scl=1 --GPIO5
          mcp9808:init(sda, scl)            -- initialize I2C     

          tp1 = mcp9808:readTemp()   -- read temperature
         =print(tp1)                              -- print it
Let’s put it together :
If all ok, we can move to the next step, how to make the data available on the web.
For this one we will need
WEB Server 
           conn:on("receive",function(conn,payload) print(payload)
           conn:send("HTTP/1.1 200 OK\n\n")
           conn:send("<META HTTP-EQUIV=\"REFRESH\" CONTENT=\"5\">")
           conn:send("<html><title>MCP9808 - Temperature Log Server - ESP8266</title><body>")
           conn:send("<h1>ESP8266 Temperature Log Server - MCP9808</h1><BR>")
           conn:send("Temperature   : <b>" .. tp1 .. "&deg;C</b><BR><BR>")
           conn:send("Node.HEAP : <b>" .. node.heap() .. "</b><BR><BR>")
           conn:send("IP ADDR    : <b>".. wifi.sta.getip() .. "</b><BR>")
           conn:send("Node MAC   : <b>" .. wifi.sta.getmac() .. "</b><br>")
           conn:send("TMR.NOW    : <b>" .. .. "</b><BR<BR><BR>")
           conn:on("sent",function(conn) conn:close() end)
 READ Temperature function
        function readTMP()
            mcp9808:init(sda, scl)
            tp1 = mcp9808:readTemp()
TIMER to establish how often we want the reading process to be done.
       -- read data every 1sec for direct web reading
       tmr.alarm(0, 1000, 1, function() readTMP() end )
 Save the code on ESP as ‘web_temp.lua‘, restart ESP and run:  
       =wifi.sta.getip()              -- find the IP Address where your Web Server will be 
        dofile("web_temp.lua")  -- Start the Web Server
 Open your favorite Web browser and type your nre Web Server IP address. If all ok, should look something like below :

So far so good. Next if you want the Web Server to start automatically when your CBDB module starts or reboots, then you neet to create and add some lines in your ‘init.lua’ file:                         -- for debug only, you can skip it
wifi.sta.getmac()              -- for debug only, you can skip it        
wifi.sta.getip()                 -- for debug only, you can skip itnode.heap()
dofile("web_temp.lua")   -- needed to start Web Server and  Temperature logger

Save the code on ESP as ‘init.lua‘, restart ESP. It should reboot and restart the program and reinitialize the Web Server.

That’s all for today, thank you for your great feedback and looking forward for your suggestions!

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