ESP8266 Community Forum

- Tue Dec 09, 2014 8:10 am #4358 I'll try to simulate negative temperatures and I'll update the example tonight.

- Tue Dec 09, 2014 5:06 pm #4433 Well, this was FUN!
I had to walk to my freezer like 6 times to put and pull the module and rewrite the code.
In the meantime, I identified a bug in the nodeMCU related to Modulo operation upon negative integer (bug is here: http://www.esp8266.com/viewtopic.php?f=18&t=795).

Until the bug is fixed, following code will work OK:

Code: Select allpin = 9
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

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

srv=net.createServer(net.TCP)
srv:listen(8080,function(conn)
    getTemp()
    t1 = lasttemp / 10000
    t2 = (lasttemp >= 0 and lasttemp % 10000) or (10000 - lasttemp % 10000)
    conn:send("Temperature: " .. t1 .. "." .. string.format("%04d", t2) .. "\n\n")
  conn:on("sent",function(conn) conn:close() end)
end)

Btw, doing XOR on my own - that's what I call challenge
The line with t2 calculation will have to be modified after the fix of the nodeMCU.
The code runs on the device on port 8080, so I can do

Code: Select allnc esp 8080

and it will reply with

Code: Select allTemperature: -9.1875

The esp is the domain name my router assigns to the device's DHCP request...

- Sat Dec 27, 2014 1:19 pm #5797 Hi sancho,
If is a single sensor DS18B20 on bus, you can replace the getTemp() with this for speed:

Code: Select allfunction getTemp()
        tmr.wdclr()     
        ow.reset(pin)
        ow.skip(pin)
        ow.write(pin,0x44,1)
        tmr.delay(800000)
        ow.reset(pin)
        ow.skip(pin)
        ow.write(pin,0xBE,1)

        data = nil
        data = string.char(ow.read(pin))
        data = data .. string.char(ow.read(pin))
        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


- Mon Dec 29, 2014 7:49 am #5890 Hi Sancho,

Great example to get DS18B20 temperatures, I am using your modified code which works with negative temperatures, I connected 2 sensors, and it appears to be very robust however, from the browser when I enter http://192.168.0.179:8080/ and I can see in uploader it gets both temperatures (don't understand why it does this twice ? ):
Last temp: 298750
Last temp: 242500
Last temp: 302500
Last temp: 241875

But on the web page I only get 1 temperature which is always the second one like in this case 24.2500, any idea how I can get this code to print out both readings from the 2 sensors on the webpage ?