nodemcu-firmware/docs/lua-modules/ds18b20.md

DS18B20 Module

Since	Origin / Contributor	Maintainer	Source
2014-12-08	Huang Rui	Huang Rui	ds18b20.lua

This Lua module provides access to DS18B20 1-Wire digital thermometer.

!!! note The module requires ow C module built into firmware.

Require

ds18b20 = require("ds18b20")

Release

ds18b20 = nil
package.loaded["ds18b20"] = nil

enable_debug()

Enables debug output of the module.

Parameters

None

Returns

nil

ds18b20.read_temp()

Scans the bus for DS18B20 sensors (optional), starts a readout (conversion) for all sensors and calls a callback function when all temperatures are available. Powered sensors are read at once first. Parasite-powered sensors are read one by one. The first parasite-powered sensor is read together with all powered sensors.

Syntax

read_temp(callback, pin, unit, force_search, save_search)

Parameters

• callback function that receives all results when all conversions finish. The callback function has one parameter - an array addressed by sensor addresses and a value of the temperature (string for integer version).
• pin pin of the one-wire bus. If nil, GPIO0 (3) is used.
• unit unit can be Celsius ("C" or ds18b20.C), Kelvin ("K" or ds18b20.K) or Fahrenheit ("F" or ds18b20.F). If not specified (nil) latest used unit is used.
• force_search if not nil a bus search for devices is performed before readout. If nil the existing list of sensors in memory is used. If the bus has not been searched yet the search performed as well.
• save_search if not nil found sensors are saved to the file ds18b20_save.lc. When read_temp is called, list of sensors in memory is empty and file ds18b20_save.lc is present then sensor addresses are loaded from file - useful when running from batteries & deepsleep - immediate readout is performed (no bus scan).

Returns

nil

Example

local t = require("ds18b20")
local pin = 3 -- gpio0 = 3, gpio2 = 4

local function readout(temp)
  if t.sens then
    print("Total number of DS18B20 sensors: ".. #t.sens)
    for i, s in ipairs(t.sens) do
      print(string.format("  sensor #%d address: %s%s",  i, ('%02X:%02X:%02X:%02X:%02X:%02X:%02X:%02X'):format(s:byte(1,8)), s:byte(9) == 1 and " (parasite)" or ""))
    end
  end
  for addr, temp in pairs(temp) do
    print(string.format("Sensor %s: %s °C", ('%02X:%02X:%02X:%02X:%02X:%02X:%02X:%02X'):format(addr:byte(1,8)), temp))
  end

  -- Module can be released when it is no longer needed
  t = nil
  package.loaded["ds18b20"] = nil
end

t:read_temp(readout, pin, t.C)

ds18b20.sens

A table with sensors present on the bus. It includes its address (8 bytes) and information whether the sensor is parasite-powered (9-th byte, 0 or 1).

ds18b20.temp

A table with readout values (also passed as a parameter to callback function). It is addressed by sensor addresses.

Notes

Other examples of using this module can be found in ds18b20-example.lua and ds18b20-web.lua files.