Send tempature (in degrees C) from a DS1820 temp chip to thingspeak.com, runs in NodeMCU on a ESP8266

ds1820.lua

-- Measure temperature and post data to thingspeak.com
-- 2014 OK1CDJ
--- Tem sensor DS18B20 is conntected to GPIO0
--- 2015.01.21 sza2 temperature value concatenation bug correction
http = require('http')
pin = 4
ow.setup(pin)

counter=0
lasttemp=-999

function bxor(a,b)
   local r = 0
   for i = 0, 31 do
      if ( a % 2 + b % 2 == 1 ) then
         r = r + 2^i
      end
      a = a / 2
      b = b / 2
   end
   return r
end

--- Get temperature from DS18B20
function getTemp()
      addr = ow.reset_search(pin)
      repeat
        tmr.wdclr()

      if (addr ~= nil) then
        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
                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)
                data = nil
                data = string.char(ow.read(pin))
                for i = 1, 8 do
                  data = data .. string.char(ow.read(pin))
                end
                crc = ow.crc8(string.sub(data,1,8))
                if (crc == data:byte(9)) then
                   t = (data:byte(1) + data:byte(2) * 256)
         if (t > 32768) then
                    t = (bxor(t, 0xffff)) + 1
                    t = (-1) * t
                   end
         t = t * 625
                   lasttemp = t
         print("Last temp: " .. lasttemp)
                end
                tmr.wdclr()
          end
        end
      end
      addr = ow.search(pin)
      until(addr == nil)
end

--- TODO: Convert to degrees F. 
--- Get temp and send data to thingspeak.com
function sendData()
  getTemp()
  t1 = lasttemp / 10000
  t2 = (lasttemp >= 0 and lasttemp % 10000) or (10000 - lasttemp % 10000)
  full_temp = t1 .. "."..string.format("%04d", t2)
  print("Temp:"..full_temp.." C\n")
  -- conection to thingspeak.com
  print("Sending data to thingspeak.com")
  http.get("184.106.153.149", 80, "/update", {key = "O63P9CRZBCKVTIS1", field1=full_temp}, function (payload)
    print(payload)
  end)
end

-- send data every X ms to thing speak
tmr.alarm(0, 60000, 1, function() sendData() end )