• ESP8266 (ESP-12F)
• ESP8266 adapter plate for making it easy (and always continuity test them!)
• DS18B20 with ~1 meter cable attached
• MCP1702 (SOT-89 for the adapter plate AND REMOVE THE 0ohm RESISTOR ON PLATE)
• Resistors: 7.5k 4.7k 1k
• 18650 battery and a holder for it

Pro tip: the “shield” on ESP8266MOD (like ESP12 etc) is grounded, and is easy to solder to if you're lazy.
Pro tip 2 / Warning: If you are new to NodeMCU, you need to get the Float version. NOT the integer version ;)

Data to GPIO4, VCC to 3.3v, GND to GND.
Connect a 4.7k resistor between 3.3v and GPIO4.

Connect 7.5k (R₁) between ADC and Battery VCC.
Connect 1k (R₂) between ADC and GND.

If you need more accuracy, please use different resistors for the voltage divider. As I wanted it to be able to measure up to 8.3v

Convert 10bit ADC back to original voltage: adc.read(0)/1024/R₂*(R₁+R₂)
Example: adc.read(0)/1024/1000*(7500+1000)

Connect GPIO16 to RST with a wire or something is all that is needed :)

There are some people on the internet, that claims you need to conenct both GPIO0 and GPIO2 with a resistor to VCC for it being able to wake from deep sleep. I tried this, and it has the opposite effect.

t = require("ds18b20")
t.setup(2)
addrs = t.addrs()
tmr.alarm(1,1000, 1, function() 
    if (wifi.sta.getip()==nil or t.read() == 85) then 
        print("Waiting for a WiFi connection or the ds18b20.") 
    else 
        print("New IP address is "..wifi.sta.getip()) 
        print("Temperature: "..t.read().."'C")
        vbatt = 0
        i=0
        while (i<10) do
             vbatt=vbatt+adc.read(0)/1024/1000*(7500+1000)
             i=i+1
        end
        tmr.stop(1) 
        conn=net.createConnection(net.TCP, false) 
        conn:on("receive", function(conn, pl) node.dsleep(300000000) end) -- 5 minutes
        conn:connect(8888,"ws.mathias.local")
        conn:send(GET /sensor?type=temp&id="..node.chipid().."&value="..t.read().."&vbatt="..(vbatt/10).." HTTP/1.1\r\nHost: ws.mathias.local\r\nConnection: keep-alive\r\nAccept: */*\r\n\r\n")       
    end 
end)

--------------------------------------------------------------------------------
-- DS18B20 one wire module for NODEMCU
-- NODEMCU TEAM
-- LICENCE: http://opensource.org/licenses/MIT
-- Vowstar <[email protected]>
-- 2015/02/14 sza2 <[email protected]> Fix for negative values
--------------------------------------------------------------------------------

-- Set module name as parameter of require
local modname = ...
local M = {}
_G[modname] = M
--------------------------------------------------------------------------------
-- Local used variables
--------------------------------------------------------------------------------
-- DS18B20 dq pin
local pin = nil
-- DS18B20 default pin
local defaultPin = 2
--------------------------------------------------------------------------------
-- Local used modules
--------------------------------------------------------------------------------
-- Table module
local table = table
-- String module
local string = string
-- One wire module
local ow = ow
-- Timer module
local tmr = tmr
-- Limited to local environment
setfenv(1,M)
--------------------------------------------------------------------------------
-- Implementation
--------------------------------------------------------------------------------
C = 'C'
F = 'F'
K = 'K'
function setup(dq)
  pin = dq
  if(pin == nil) then
    pin = defaultPin
  end
  ow.setup(pin)
end

function addrs()
  setup(pin)
  tbl = {}
  ow.reset_search(pin)
  repeat
    addr = ow.search(pin)
    if(addr ~= nil) then
      table.insert(tbl, addr)
    end
    tmr.wdclr()
  until (addr == nil)
  ow.reset_search(pin)
  return tbl
end

function readNumber(addr, unit)
  result = nil
  setup(pin)
  flag = false
  if(addr == nil) then
    ow.reset_search(pin)
    count = 0
    repeat
      count = count + 1
      addr = ow.search(pin)
      tmr.wdclr()
    until((addr ~= nil) or (count > 100))
    ow.reset_search(pin)
  end
  if(addr == nil) then
    return result
  end
  crc = ow.crc8(string.sub(addr,1,7))
  if (crc == addr:byte(8)) then
    if ((addr:byte(1) == 0x10) or (addr:byte(1) == 0x28)) then
      -- print("Device is a DS18S20 family device.")
      ow.reset(pin)
      ow.select(pin, addr)
      ow.write(pin, 0x44, 1)
      -- tmr.delay(1000000)
      present = ow.reset(pin)
      ow.select(pin, addr)
      ow.write(pin,0xBE,1)
      -- print("P="..present)
      data = nil
      data = string.char(ow.read(pin))
      for i = 1, 8 do
        data = data .. string.char(ow.read(pin))
      end
      -- print(data:byte(1,9))
      crc = ow.crc8(string.sub(data,1,8))
      -- print("CRC="..crc)
      if (crc == data:byte(9)) then
        t = (data:byte(1) + data:byte(2) * 256)
        if (t > 32767) then
          t = t - 65536
        end

        if (addr:byte(1) == 0x28) then
          t = t * 625  -- DS18B20, 4 fractional bits
        else
          t = t * 5000 -- DS18S20, 1 fractional bit
        end

        if(unit == nil or unit == 'C') then
          -- do nothing
        elseif(unit == 'F') then
          t = t * 1.8 + 320000
        elseif(unit == 'K') then
          t = t + 2731500
        else
          return nil
        end
        t = t / 10000
        return t
      end
      tmr.wdclr()
    else
    -- print("Device family is not recognized.")
    end
  else
  -- print("CRC is not valid!")
  end
  return result
end

function read(addr, unit)
  t = readNumber(addr, unit)
  if (t == nil) then
    return nil
  else
    return t
  end
end

-- Return module table
return M