Raspberry PI Temperature Sensor

The Raspberry Pi (PI) is pretty nifty little device. I have done various programming projects with it over the past seven to nine months. A few days ago a had a strong drive to experiment with the PI's GPIO interface and connect a heat sensors to measure temperatures.

This project comprises of three distinct phases namely: a) Electronics Circuitry, b) Software Development and c) Testing and Integration.

a) Electronics Circuitry (EC): The EC phase entails the assembly of the temperature components as a complete unit onto the breadboard. One of the Dallas sensor is placed directly on the breadboard, The second sensor is wired on the other end of the ethernet cable.

b) Software Development (SD): The SD phase entails preparing the suitable software application to control and manage the EC assembly. Various option exist which languages could be used to develop an application to read, process and store temperature readings. Python is an excellent choice and probably the easiest. However, I am Pascal kind of person both on Windows and Linux operating systems.
Bear in mins that in the absence of any form of a software package, the PI is not able to make any temperature readings, even if the sensors are connected correctly to the GPIO pins. My SD environment is as follows:

• Free Pascal compiler in CLI mode to develop an executable that takes readings from the senors.

• Sqlite 3 database to store the temperature readings as per the FPC CLI program.

• A cron job to run the FPC program every 5 minutes.

c) Testing and Integration (T&I): TI in essence means integrating the EC and SD components into a single functional module.

My bill of materials was:

• 1x Raspberry Pi 2 B (including PSU, card and box).
• 2x Dallas DS18B20 temperature sensors.
• 1x 4K7 Ω resistor.
• 1x Breadboard.
• A dozen male to female jumper wires.
• 1x 3m long UTP ethernet cable.

The final assembly is illustrated in the image below:

Raspberry PI with Temperature sensors on a Breadboard

The sensor on the ethernet cable is temporarily placed outside a room to measure the outdoor temperatures while the breadboard is placed indoors. Below is an extract form the temperature log file (csv formatted with the temperature in celsius degrees being the last 3 characters): 

2016-01-04 00:00:01,28-000006df1322,27.5

2016-01-04 00:00:02,28-0000059a01ed,22.7

2016-01-04 00:05:02,28-000006df1322,27.5

2016-01-04 00:05:03,28-0000059a01ed,22.6

2016-01-04 00:10:02,28-000006df1322,27.5

2016-01-04 00:10:03,28-0000059a01ed,22.6

2016-01-04 00:15:02,28-000006df1322,27.5

2016-01-04 00:15:03,28-0000059a01ed,22.4

2016-01-04 00:20:02,28-000006df1322,27.4

2016-01-04 00:20:03,28-0000059a01ed,22.4

The listing below comprises the complete Pascal program used to read and store temperature readings into  Sqlite 3 database table:

program tempsensors;

{$mode objfpc}

uses Classes, SysUtils, db, sqlite3ds;

const appVersion = '0.1';

var sl       : TStringlist;
    rows     : integer;
    temp     : string;
    slDevs   : TStringlist; //devicesList
    i        : integer;
    devCount : integer;
    devFile  : string;

    logOutput : string;

    dsTempLog : TSqlite3Dataset;
    sqlstr  : string;

function parseTemperature(tempStr: string):string;
{*
 Function parses and returns a temperature value from the given string tempStr.
 tempStr = temperature string.
*}
var
    x : integer;   //index used to parse temperature value in a string.
    c : integer;   //temperature reading in celsius.
    f : real;      //temperature value / 1000.

begin
 result := '';

 if tempStr = '' then
 exit;

 x := pos('=', tempStr) + 1;

 begin
   c := strtoint(copy(tempStr,x,5));
   f := c/1000;

   result := floatToStrF(f,ffFixed,2,1);
 end;
end;


function logDateStamp:string;
var current : TDateTime;
begin
 current := now;

 result := formatDateTime('YYYY/MM/DD hh:mm:ss', current);
end;


procedure logToTextFile(aFn, aLogdata: string);
var fh : TextFile;   //filename to log to.
begin
 assignFile(fh,aFn);

 if not fileExists(aFn) then
 begin
   rewrite(fh);
 end
 else
 begin
   append(fh);
 end;

 try
   writeln(fh,aLogData);
 finally
   closeFile(fh)
 end;
end;

begin {begin of main program.}

// writeln('Script started by user.');
// writeln('Hello Pascal on Raspberry Pi.');


 //Exit this program if prescribed file does not exists:
 if not fileExists('/home/pi/progs/pascal/sensorDevices.txt') then
 begin
   writeln('Alert: Error in opening the sensor devices descriptor file.');
   exit;
 end;


 //Load into the devces stringlist a text file that contains declared sensor devices:
 slDevs := TStringlist.create;

 dsTemplog := TSqlite3Dataset.create(nil);
 dsTemplog.Filename   := '/home/pi/progs/pascal/templog.db';
 dsTemplog.Tablename  := 'temps';
 dsTemplog.PrimaryKey := 'id';

 try
   slDevs.loadfromfile('/home/pi/progs/pascal/sensorDevices.txt');

   devCount := slDevs.count;

   //Declare String list that will hold conrtents of sensor device w1_slave file contents:
   sl := TStringlist.create;


   try
      //Iterate through each device file name
      for i := 0 to devCount-1 do
      begin
         logOutput := '';

         devFile := '/sys/bus/w1/devices/' + slDevs[i] + '/w1_slave';

         if not fileexists(devFile) then
         begin
            writeln('Alert: Sensor device system file not found.');
            exit;
         end;

         //Load fiel contents of w1_slave file to extract the temperature:
         sl.loadfromfile(devFile);

         rows := sl.count;

         //Display temperature log reading if prescribed conditions are met, else display error message.
         if (rows = 2) and (pos('YES', sl[0]) > 0)  then
         begin
            temp := sl[1];
            writeln('Processing  device with index : [' + inttostr(i) + ']. Row count: ' + inttostr(rows));
            logOutput := logDateStamp + ',' + slDevs[i] + ',' + parseTemperature(temp);

            writeln(logOutput);

            try
{               sqlstr := 'insert into temps (date_log,device_id,temp) ' +
                         'values ' +
                         '(%f, ''%s'', %f)';
}

               //Construct the SQL insert statement
               sqlstr := 'INSERT INTO temps ' +
                         '(date_log,device_id, temp) ' +
                         'VALUES '+
                         '('''+logDateStamp+''','+''''+slDevs[i]+''','+''''+parseTemperature(temp)+''')';

//               dsTemplog.sql := Format(sqlstr, [logDateStamp, slDevs[i], parseTemperature(temp)]);
//               dsTemplog.sql := Format(sqlstr, ['2016-01=03 10:00:00', slDevs[i], '28.0']);
               dsTemplog.sql := sqlstr;
               dsTemplog.ExecSql;
            except
              writeln('Alert: Error in inserting data to the DB table with sql statement:');
              writeln(sqlstr);
            end;

            logToTextFile('/home/pi/progs/pascal/tempreadings.log',logOutput);
         end
         else
         begin
            writeln('Alert: Temperature string not found');
          end;
      end;
   finally
      sl.free;
   end;
 finally
   dsTemplog.free;
   slDevs.free;
 end;

end.

Going forward my intention is to:

• Duplicate the project on a Raspberry PI Zero.
• Add a dozen more DS18B20 temperature sensors.
• Provide environmental proofing of the sensors.
• Develop a web portal that accesses the Sqlite table for display and control capabilities.

A Web Portal in Dart

In my previous post I shared my initial views on programming with Dart. To date I have developed a few projects, both in the private and business realm, and my experiences have been extremely favourable.

The most recent projects entailed a web portal for company. Considering that my Javascriot/JQuery has never been my strength, Dart evolved as a natural substitute for the limited PHP/JQuery skills set I had. The high level features of the web portal are:

• Web technology based portal.
• Dart front end.
• JSON based back end integration.
• User login based access control.

Web Portal in Dart

Needless to say, the back end server is developed in PHP and primarily serves to interface the portal to a MySQL database by means of JSON. However, in the future the PHP implementation will be replaced by either a Golang or Dart version.

Below is a code snippet used to render the most recent articles on the portal:

void xhrFetchJson_articles(HttpRequest request, String aContext, String aUrlAction) {
  /* 
   * Function is used to list actual imagery content as retrieved from a database table.
   * 
   * 1. This function initiates an HttpRequest to fetch json data from a PHP backend script.
   * 2. The JSON data is decoded in a dart Map structure to enable the relevant fields.
   * 3. The relevant MAP structure fields are the used to generate a table that includes an edit buton.
  */  
    
  print("[Debug] Evoked function rxhrFetchJson_articles");
  print("[Debug] Function argument aContext   = " + aContext);
  print("[Debug] Function argument aUrlAction = " + aUrlAction);
  print("[Debug] ---------------End.");

  if(request.status == 200) {
    print("[Debug] function xhrFetchJson_articles Data fetched from http server (200).");
    
    if(request.responseText == "zero.rows.found"){
      
      window.alert("Alert: No content found.");
      querySelector("#output").appendHtml(gallery.displayGallery_WIP("images/contentnotfound.png"));
      
      return;
  }
  
  //Proceeed if valid content has been returned:
    
    //Debug messages to print responsetext received from the xhr function: 
//      print(request.responseText);
    
    querySelector("#output").text = "";

    JsonObject data = new JsonObject.fromJsonString(request.responseText);    
    
    String aArticleAuthor   = "";
    String aArticleTitle    = "";
    String aArticlePubDate  = "";
    String aArticleText     = "";
    String aArticleImageUrl    = "";
    
    //Loop through the JSON data instance and creaye a link navigation menus:
    for(int i = 0; i < data.length; i++) {
      aArticleAuthor    = data[i].author.toString();
      aArticleTitle     = data[i].title.toString();
      aArticlePubDate   = data[i].date_pub.toString();
      aArticleText      = data[i].article_text.toString();
      aArticleImageUrl     = data[i].url_image_intro.toString();
      
//      displayNews_Content(String aTitle, String aAuthor, String aPubDate, String aArticleText, String aFilename) {

      querySelector("#output").appendHtml(displayNews_Content(aArticleTitle,
                                                              aArticleAuthor,
                                                              aArticlePubDate,
                                                              aArticleText,
                                                              aArticleImageUrl));
            
    }
    
  }    
}

In comparison to other web oriented development environments I have used before, I really found that Dart is a very capable, suitable  and powerful in its ability to manipulate the HTML DOM and processing of JSON interfaces.

It may be  noteworthy to mention that 3rd party frameworks are not incorporated into the web application. However, I did make use of a 3rd party JSON Object library as indicated below:

import 'dart:html';
import 'package:json_object/json_object.dart';
//import 'dart:convert';
//import 'nlc_serverroom.dart' as server;
import 'nlc_lib_contacts.dart' as contacts;
import 'nlc_lib_galleries.dart' as gallery;
import 'nlc_lib_pbx.dart' as pbx;
import 'nlc_lib_assets.dart' as assets;
import "fn_authentication.dart" as libAuthenticate;
import 'trials.dart' as trial;
import 'package:intl/intl.dart';