温度測定を題材にラズパイIoTシステムの「収集」「蓄積」「活用」を理解する：ラズパイで製造業のお手軽IoT活用（2）（4/4 ページ）

小型ボードコンピュータ「Raspberry Pi（ラズパイ）」を使って低コストかつ現場レベルで導入できる手法について解説する本連載。第2回は、温度測定ツールを題材に、データの「収集」から「蓄積」、「活用（可視化）」までを行う流れについて具体的に解説します。

[株式会社アムイ 代表取締役 山田浩貢，MONOist]

※本記事はアフィリエイトプログラムによる収益を得ています

記事に使用したサンプルソースのテキスト

import glob
import time
import subprocess
import sqlite3
import threading
base_dir = '/sys/bus/w1/devices/'
device_folder = glob.glob(base_dir + '28*')[0]
device_file = device_folder + '/w1_slave'
db_file = '/home/pi/MTS/temperature.sqlite3'
def read_temp_raw():
 catdata = subprocess.Popen(['cat',device_file], stdout = subprocess.PIPE, stderr = subprocess.PIPE)
 out, err = catdata.communicate()
 out_decode = out.decode('utf-8')
 lines = out_decode.split('\n')
 return lines
def read_temp():
 lines = read_temp_raw()
 if lines[0].strip()[-3:] != 'YES':
  return False
 equals_pos = lines[1].find('t=')
 temp_string = lines[1][equals_pos + 2:]
 temp_c = float(temp_string) / 1000.0
 return temp_c
def save_temp():
 try:
  connection = sqlite3.connect(db_file)
  cursor = connection.cursor()
  temp = read_temp()
  if temp:
   cursor.execute("INSERT INTO DATE_TEMPERATURE VALUES (strftime('%Y/%m/%d', date('now', 'localtime')), strftime('%H:%M:%S',time('now', 'localtime')), ?);", (temp,))
   connection.commit()
 except:
  connection.rollback()
 finally:
  connection.close()
while True:
 th = threading.Thread(target=save_temp)
 th.start()
 time.sleep(3)

リスト1　「mt.py」のサンプルソースコード

<?php
 $dataNum = 180;
 $check = false;
 while ($check == false) {
  try {
   $db = new SQLite3("/home/pi/MTS/temperature.sqlite3", SQLITE3_OPEN_READONLY);
   $date = date("Y/m/d");
   $sql = "select * from DATE_TEMPERATURE where DATE = '" . $date . "' order by TIME desc limit " . $dataNum . ";";
   $res = $db->query($sql);
   $i = 0;
   while ($t = $res->fetchArray(SQLITE3_NUM)) {
    $b[$i] = $t;
    $i += 1;
   }
   for ($k = 0; $k < $dataNum - $i; $k++) {
    $a[$k][0] = $a[$k][1] = "";
    $a[$k][2] = "null";
   }
   for ($k = 0; $k < $i; $k++) {
    $a[$dataNum - $i + $k] = $b[$i - $k - 1];
   }
   $check = true;
  } catch (Exception $e) {
   $i = 0;
   $check = false;
   usleep(10000);
  } finally {
   $db->close();
   $db = null;
  }
 }
 $str = "[";
 for ($k = 0; $k < $dataNum; $k++) {
  $str .= "'" . $a[$k][1] . "'," . $a[$k][2] . ",";
 }
 $str .= "]";
 echo $str;
?>

リスト2　「jsonTemps.php」のサンプルソースコード

  <script>
   var today = new Date();
   var date = '' + today.getFullYear() + ('00' + (today.getMonth() + 1)).substr(-2) + ('00' + today.getDate()).substr(-2);
   var xhr
   var xhr2;
   var times = new Array();
   var temps = new Array();
   var ctx;
   var chart;
   var color;
   onload = function(){
    ctx = document.getElementById('temp').getContext('2d');
    updateGraph();
    setInterval(updateGraph, 1000);
   }
   function updateGraph(){
    xhr = new XMLHttpRequest();
    xhr.onreadystatechange = myupdate;
    xhr.open("GET", "jsonTemps.php?date=" + date);
    xhr.send(null);
   }
   function myupdate(){
    if (xhr.readyState == 4 && xhr.status == 200) {
     list = eval('(' + xhr.responseText + ')');
     for (var i = 0; i < list.length / 2; i++) {
      times[i] = list[2 * i];
      temps[i] = list[2 * i + 1];
     }
     drawChart();
    }
   }
   
   function startMt(){
    xhr2 = new XMLHttpRequest();
    xhr2.open("GET", "startMt.php");
    xhr2.send(null);
   }
  function stopMt(){
   xhr2 = new XMLHttpRequest();
   xhr2.open("GET", "stopMt.php");
   xhr2.send(null);
  }
  </script>
  <script>
   function drawChart() {
    if (typeof chart != 'undefined') chart.destroy();
    color = "rgb(100, 200, 200)";
    chart = new Chart(ctx, {
     type: "line",
     data: {
      labels: times,
      datasets: [{
       label: "温度",
       lineTension: 0,
       fill: false,
       backgroundColor: color,
       borderColor: color,
       data: temps,
      }]
     },
     options: {
      responsive: false,
      animation: false,
      scales: {
       xAxes: [{
        scaleLabel: {
         display: true,
         labelString: date
        }
       }],
       yAxes: [{
        scaleLabel: {
         display: true,
         labelString: "温度(℃)"
        },
        ticks: {
         min: -20,
         max: 120
        }
       }]
      }
     }
    });
   }
  </script>

リスト3　「latest.html」のサンプルソースコード