ESP8266 and DS18B20: Transmitting Temperature Data

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I’m ready to tie together much of what I’ve learned to read a DS18B20 temperature sensor using the oneWire protocol and transmit the temperature via UDP to an echo server. (In a future post I will act upon the received data.)

Wiring the Sensor

Very straight forward:

here is what it looks like:

Testing the DS18B20

I entered the following onewire/ds18b20 test code straight into my ESP8266, just changing the pin:

https://github.com/nodemcu/nodemcu-firmware/blob/master/lua_examples/onewire-ds18b20.lua

This worked fine:

40    23    200    64    5    0    0    9
Device is a DS18S20 family device.
P=1
177    1    75    70    127    255    15    16    141
CRC=141
Temperature= 27.625 Centigrade

I decided to make a few changes so I could see the address and data in hex form:

pin = 4
ow.setup(pin)
count = 0
repeat
  count = count + 1
  addr = ow.reset_search(pin)
  addr = ow.search(pin)
  tmr.wdclr()
until((addr ~= nil) or (count > 100))
if (addr == nil) then
  print("No more addresses.")
else
  --print(addr:byte(1,8))
  s=string.format("Addr:%02X-%02X-%02X-%02X-%02X-%02X-%02X-%02X", 
    addr:byte(1),addr:byte(2),addr:byte(3),addr:byte(4), 
    addr:byte(5),addr:byte(6),addr:byte(7),addr:byte(8))
  print(s)
  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.")
        repeat
          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))
          s=string.format("Data:%02X-%02X-%02X-%02X-%02X-%02X-%02X-%02X", 
            data:byte(1),data:byte(2),data:byte(3), data:byte(4),
            data:byte(5),data:byte(6), data:byte(7),data:byte(8))
          print(s)
          crc = ow.crc8(string.sub(data,1,8))
          --print("CRC="..crc)
          s=string.format("CRC: %02X", crc)
          print(s)
          if (crc == data:byte(9)) then
             t = (data:byte(1) + data:byte(2) * 256) * 625
             t1 = t / 10000
             t2 = t % 10000
             print("Temperature= "..t1.."."..t2.." Centigrade")
          end                   
          tmr.wdclr()
        until false
    else
      print("Device family is not recognized.")
    end
  else
    print("CRC is not valid!")
  end
end

getTemp: Function to Return Current Temperature

Once I knew I could access the DS18B20, I reworked the code into a function that, when called, simply returns the temperature. It returns the temp with an implied decimal point, 4 places from the right (99V9999):

function getTemp()

    local addr      = nil
    local count     = 0
    local data      = nil
    local pin       = 4             -- pin connected to DS18B20
    local s         = ''

    -- setup gpio pin for oneWire access
    ow.setup(pin)

    -- do search until addr is returned
    repeat
        count   = count + 1
        addr    = ow.reset_search(pin)
        addr    = ow.search(pin)
        tmr.wdclr()
        until((addr ~= nil) or (count > 100))

    -- if addr was never returned, abort
    if (addr == nil) then
        print('DS18B20 not found')
        return -999999
        end
  
    s=string.format("Addr:%02X-%02X-%02X-%02X-%02X-%02X-%02X-%02X", 
        addr:byte(1),addr:byte(2),addr:byte(3),addr:byte(4), 
        addr:byte(5),addr:byte(6),addr:byte(7),addr:byte(8))
    --print(s)

    -- validate addr checksum
    crc = ow.crc8(string.sub(addr,1,7))
    if (crc ~= addr:byte(8)) then
        print('DS18B20 Addr CRC failed');
        return -999999
        end

    if not((addr:byte(1) == 0x10) or (addr:byte(1) == 0x28)) then
        print('DS18B20 not found')
        return -999999
        end
        
    ow.reset(pin)               -- reset onewire interface
    ow.select(pin, addr)        -- select DS18B20
    ow.write(pin, 0x44, 1)      -- store temp in scratchpad
    tmr.delay(1000000)          -- wait 1 sec
    
    present = ow.reset(pin)     -- returns 1 if dev present
    if present ~= 1 then
        print('DS18B20 not present')
        return -999999
        end
    
    ow.select(pin, addr)        -- select DS18B20 again
    ow.write(pin,0xBE,1)        -- read scratchpad

    -- rx data from DS18B20
    data = nil
    data = string.char(ow.read(pin))
    for i = 1, 8 do
        data = data .. string.char(ow.read(pin))
        end
    
    s=string.format("Data:%02X-%02X-%02X-%02X-%02X-%02X-%02X-%02X", 
        data:byte(1),data:byte(2),data:byte(3), data:byte(4),
        data:byte(5),data:byte(6), data:byte(7),data:byte(8))
    --print(s)

    -- validate data checksum
    crc = ow.crc8(string.sub(data,1,8))
    if (crc ~= data:byte(9)) then
        print('DS18B20 data CRC failed')
        return -9999
        end

    -- compute and return temp as 99V9999 (V is implied decimal-a little COBOL there)
    return (data:byte(1) + data:byte(2) * 256) * 625
    
    end -- getTemp

This function is tested by simply sending

> =getTemp()
246250
>

The temperature returned is 24.6250 degrees Celsius.

xmitTemp: Transmitting the Temperature

Now I need a function that will get the temperature and transmit it via UDP. Note that the temp is converted to a string before sending it.

function xmitTemp()
    local temp = 0

    temp = getTemp()

    -- if something went wrong, don't transmit
    if temp == -999999 then
        return
        end

    -- transmit the temperature to the host
    cu:send(tostring(temp))

    end -- xmitTemp

Initialization

I need to initialize networking which I do with this function:

function initWIFI()
    print("Setting up WIFI...")

    wifi.setmode(wifi.STATION)

    wifi.sta.config("SSID","PASSWORD")
    wifi.sta.connect()
    tmr.alarm(1, 1000, 1,   
        function() 
            if wifi.sta.getip()== nil then 
                print("IP unavailable, Waiting...") 
            else 
                tmr.stop(1)
                print("Config done, IP is "..wifi.sta.getip())
                end 
            end -- function
        )
    end -- initWIFI

and setup the UDP connection. I am setting up a UDP connection to the echo service on my Raspberry Pi which allows me to easily verify that the ESP8266 is properly transmitting:

function initUDP()

    -- setup UDP port
    cu=net.createConnection(net.UDP)
    cu:connect(7,"192.8.50.106")
    end -- initUDP

Tying it Together

Finally, the initialization functions must be called, and then xmitTemp is called based on a timer. For my initial testing, I am using a 10 second interval.

initWIFI()
initUDP()
tmr.alarm(0, 10000, 1, xmitTemp)

The Entire Program

Using my prior idea for init.lua, here is my init.lua which allow boot termination by setting the abort variable:

function startup()
    if abort == true then
        print('startup aborted')
        return
        end
    print('Starting xmitTemp')
    dofile('xmitTemp.lua')
    end

abort = false
print('Startup in 5 seconds')
tmr.alarm(0,5000,0,startup)

and here is the xmitTemp.lua program in its entirety:

function getTemp()

    local addr      = nil
    local count     = 0
    local data      = nil
    local pin       = 4             -- pin connected to DS18B20
    local s         = ''

    -- setup gpio pin for oneWire access
    ow.setup(pin)

    -- do search until addr is returned
    repeat
        count   = count + 1
        addr    = ow.reset_search(pin)
        addr    = ow.search(pin)
        tmr.wdclr()
        until((addr ~= nil) or (count > 100))

    -- if addr was never returned, abort
    if (addr == nil) then
        print('DS18B20 not found')
        return -999999
        end
  
    s=string.format("Addr:%02X-%02X-%02X-%02X-%02X-%02X-%02X-%02X", 
        addr:byte(1),addr:byte(2),addr:byte(3),addr:byte(4), 
        addr:byte(5),addr:byte(6),addr:byte(7),addr:byte(8))
    --print(s)

    -- validate addr checksum
    crc = ow.crc8(string.sub(addr,1,7))
    if (crc ~= addr:byte(8)) then
        print('DS18B20 Addr CRC failed');
        return -999999
        end

    if not((addr:byte(1) == 0x10) or (addr:byte(1) == 0x28)) then
        print('DS18B20 not found')
        return -999999
        end
        
    ow.reset(pin)               -- reset onewire interface
    ow.select(pin, addr)        -- select DS18B20
    ow.write(pin, 0x44, 1)      -- store temp in scratchpad
    tmr.delay(1000000)          -- wait 1 sec
    
    present = ow.reset(pin)     -- returns 1 if dev present
    if present ~= 1 then
        print('DS18B20 not present')
        return -999999
        end
    
    ow.select(pin, addr)        -- select DS18B20 again
    ow.write(pin,0xBE,1)        -- read scratchpad

    -- rx data from DS18B20
    data = nil
    data = string.char(ow.read(pin))
    for i = 1, 8 do
        data = data .. string.char(ow.read(pin))
        end
    
    s=string.format("Data:%02X-%02X-%02X-%02X-%02X-%02X-%02X-%02X", 
        data:byte(1),data:byte(2),data:byte(3), data:byte(4),
        data:byte(5),data:byte(6), data:byte(7),data:byte(8))
    --print(s)

    -- validate data checksum
    crc = ow.crc8(string.sub(data,1,8))
    if (crc ~= data:byte(9)) then
        print('DS18B20 data CRC failed')
        return -9999
        end

    -- compute and return temp as 99V9999 (V is implied decimal-a little COBOL there)
    return (data:byte(1) + data:byte(2) * 256) * 625
    
    end -- getTemp

function xmitTemp()
    local temp = 0

    temp = getTemp()
    if temp == -999999 then
        return
        end

    cu:send(tostring(temp))

    end -- xmitTemp

function initUDP()

    -- setup UDP port
    cu=net.createConnection(net.UDP)
    cu:connect(7,"192.8.50.106")
    end -- initUDP
    
function initWIFI()
    print("Setting up WIFI...")

    wifi.setmode(wifi.STATION)

    wifi.sta.config("SSID","PASSWORD")
    wifi.sta.connect()
    tmr.alarm(1, 1000, 1,   
        function() 
            if wifi.sta.getip()== nil then 
                print("IP unavailable, Waiting...") 
            else 
                tmr.stop(1)
                print("Config done, IP is "..wifi.sta.getip())
                end 
            end -- function
        )
    end -- initWIFI

initWIFI()
initUDP()
tmr.alarm(0, 10000, 1, xmitTemp)

This program works great. Upon initialization, it gets the network running, sets up the UDP connection, then starts transmitting temperature packets every 10 seconds: