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%%% @author Guido Günther <agx@sigxcpu.org>
%%% @copyright (C) 2016, Guido Günther
%%% @doc
%%% Read and write GPIO values from userspace
%%%
%%% @reference http://www.raspberrypi-spy.co.uk/2013/03/raspberry-pi-1-wire-digital-thermometer-sensor/
%%% @end
%%% License: LGLv3
-module(w1therm).
-define(W1_BASE, "/sys/bus/w1/devices/").
-export([get_therms/0,
read_temp/1]).
-type therm() :: string().
% @doc: Get 1wire temperature famliy sensors
-spec get_therms() -> {ok, list(therm())} | {error, atom()}.
get_therms() ->
case file:list_dir(?W1_BASE) of
{error, enoent} -> {ok, []};
{error, Error} -> {error, Error};
{ok, Files} ->
{ok, R} = re:compile("^[0-9]{2}-.*"),
Names = [ X || X <- Files, nomatch /= re:run(X, R)],
{ok, Names}
end.
% @doc: Read temperature from 1wire therm device in ⁰C
-spec read_temp(Therm::therm()) -> {ok, float()} | {error, atom()}.
read_temp(Therm) ->
Sysfs = therm_sysfs_path(Therm, w1_slave),
{ok, Data} = file:read_file(Sysfs),
Last = string:sub_word(binary:bin_to_list(Data), 2, $\n),
TempStr = string:sub_word(Last, 2, $=),
{Temp, []} = string:to_integer(TempStr),
{ok, Temp / 1000.0}.
% private functions
-spec therm_sysfs_path(Therm::therm(), atom() | binary()) -> string().
therm_sysfs_path(Therm, File) ->
io_lib:format(?W1_BASE ++ Therm ++ "/~p", [File]).
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