Google Analytics

Monday, July 4, 2016

Security System - Local Alarm From Kit

As part of my Security System, I wanted to place an audible alarm near whatever sensor I'm using.

My sensors are going to be networked, feeding information to the main security control.  Currently I'm using a NodeMCU which makes use of a ESP8266's WiFi network capabilities.  This also means I can send a request, from the main security control, to turn on the alarm remotely, should I desire to do so, as its under the control of the ESP8266 device.

In this post, I'm not showing any type of sensor.  However, in most cases, I'll be using a PIR or a ultrasonic sensor to set the ESP8266 in alarm output for pin 5, and then enabling the local sensor alarm sound.  So, I'm just showing the alarm device and ESP8266 here.

Because the ESP8266 is a 3.3 vdc device, it can only supply 3.3 vdc and a limited amount of current; this wasn't enough to directly drive the audible alarm, so I've added a switching transistor to supply the switching current.

Scroll down for circuit description, construction, and construction photos.

In this post, I'm showing the use of a cheap commercial Window and Door Open/Closed Sensor Alarm, that I picked up for $1.00 at a local Dollar Store.  It contains a circuit board with:

  • square wave generator
  • battery holder
  • transformer
  • on/off switch
  • piezo electric speaker
  • 3 1.5 vdc batteries

I'm not making use of the magnetic switch in this post.  Instead, I'm making use of the audible piezo alarm (hereafter referred to as ALARM), when enabled by the NodeMCU device.

Circuit Description
In this design (software in a later post), the NodeMCU is driving pin 5 high to 3.3 VDC.  The output of this pin is connected to a 6.8K resistor, then to the base of a 2N3904 NPN transistor, which is biased as a switch.

The negative battery post of the ALARM has been separated from the ALARM circuit board, with the transistor inserted between the negative battery post and the circuit board, with the ALARM circuit board connected to the transistor's collector, and the negative terminal connected to the circuit common ground.

When a high value (3.3vdc) is applied to the base of the transistor, it turns on, basically connecting the circuit board through the transistor to ground - the ALARM sounds.

When a negative value (0vdc) is applied to the base of the transistor, it turns off, stopping current flowing from the collector to the emitter, so that the circuit is open, and no ALARM sounds.

Any 3.3vdc supply can be applied to the base to turn the transistor on - you don't have to use a NodeMCU.

If other voltages are used, such as a 5vdc from an Arduino, then you should resize the base resistor.

The 2N3904 has a beta of around 200 (varies somewhat), and is limited to 200ma and 625mwatts.

I wanted to restrict the current through the transistor to 100ma.

For 100ma at 3.3vdc and beta of 200, this equates to:
CollectorCurrent (Ic) = BaseCurrent(Ib) x Beta(200)
Ic = Ib x Beta
Ib = Ic / Beta
Ib = 100ma / 200
Ib = .5ma

Base Resistor (Br) = Vdc/ma
Br = 3.3/.5ma
Br = 6.6Kohm

While I'm showing 3.3 vdc above, a closer approximation would be 3.3 - .7 = 2.6 vdc, which includes the voltage drop across the base-emitter, which would yield about 76 ma instead of the 100 ma.  However, that's good enough for this circuit, and the 6.8K is close enough, and it sound loud enough for a local alert for me; the main security controller will driving the loud stuff.

The battery voltage of 4.5 (3x1.5)vdc is flowing from the ALARM's batteries, and is being switched via the transistor's base of 3.3vdc.

This ALARM can be used in any device with a small voltage to switch the transistor on and off, by making adjustments to the base resistor.  I've put one, with a much larger value resistor into a box, so I can use it as a beeper for simple circuit tests and continuity tests; the higher value resistor limits the sound!


Construction Pictures:

The device I bought for $1.00 at the local Dollar Store

The contents of the device: 3 1.5vdc batteries, a magnet, and the sensor/alarm/battery case.

Remove the battery cover, then remove the screw I'm pointing at in order to get into the back of the case.

After you've opened the case, this what it will look like.

Two board types in stock!  Both work the same for our purposes!  We are only using the red wire where it connects to the negative battery terminal post.

Newer Device Circuit Board - pointing at black blob.
While building the circuit, I realized there were two (2) versions of the device, both bought at the same time from the same Dollar Store.  This is the newer device, showing a 'black blob' where the square wave generator is located.

Older Device Circuit Board - pointing at discrete components.
This works the same as the newer board.

Unsolder the red wire from this junction - it is the negative battery post.  Leave the other end of the red wire still connected to the circuit board.  We will be inserting the transistor between this negative battery post and the red wire, so the transistor, in acting like a switch; allowing current to flow back to the negative battery post when transistor enabled, and no current when transistor disabled.

Connect a green wire to the negative batter post you just removed the red wire from above.  This will be connected to our circuit common.

Next we are going to connect a yellow wire to the red wire that was removed from the negative battery post previously.  So, solder it in already!  Our transistor will be going between this yellow wire and green wire.

This is how the circuit will function.  The green wire is connected to ground, the yellow wire is connected to the collector of the 2N3904 NPN transistor.  The emitter is connected to ground.  The base is connected to a 6.8K resistor, and then to the output pin 5 of the NodeMCU device, which will switch 0 - 3.3vdc.

There isn't anywhere in the ALARM case for the two new wires to pass, so I used my soldering iron to melt a small hole in the case, then put the wires in, and closed up the case.

Testing!  A simple test of just the wiring changes!
Before transistor and software are added to the circuit!

I've inserted the batteries (polarity as indicated in the battery compartment bottom), and made sure to slide the switch to 'On' position - it won't sound if you don't turn it on!

With everything on, and the two wires not connected, the ALARM should not be making an alarm sound.

With everything on, and shorting the yellow and green wires together, the ALARM should be making an alarm sound!

Circuit schematic.

Using the NodeMCU with software I created, testing.  High output from NodeMCU pin 5 (also showing on blue LED on NodeMCU) causes ALARM to sound alarm.

Using the NodeMCU with software I created, testing.  Low output from NodeMCU pin 5 (also showing no LED on NodeMCU) causes ALARM to not sound alarm.

I'll upload the software in a later, separate post.


Wednesday, February 17, 2016

Home Security/Automation System - New Design!

Design Update  (February 17, 2016)
Previous     Next     Table of Contents

Well, if you've been following this blog from the start, then you know that I've had a lot of hurdles to overcome!

My background in programming, while extensive (beginning in 1977) and including many programming languages, did not have any real front-end presentation layer activities.  So, with no front end stuff, then no HTML, no Javascript, no Nodejs, no Express, no Jade.....just a lot of "no's!".

Since I had a lot of Java background, that was my first approach.  But it was just too heavy for my target hardware - a Beaglebone Black.  Also, I was tired of programming in it!  Since I was now retired, I decided I wanted something more efficient than Java, both from a programming standpoint, as well as a system load standpoint (Beaglebone remember!).

My search led me to Python.  I considered Scalia and Ruby, but Python looked good to me, and was something I could easily use on future code for around the house.  So, I started planning on Python.  But I ran into a problem on the front end presentation layer - not much better than what I was used to in Java!   But I kept going...see my posts on Kivy on this blog.

Life intervened, and I had to stop the project for a while.  But I kept occasionally researching, and somewhere came across nodejs.  This really peaked my interest.

I dug into nodejs (note: this is the new, correct spelling for this product; after their recent merger, then changed the name from node to nodejs).  I really liked what I saw.  That, along with the ability to push data to a HTML5 browser (I refused to do polling) meant I could move off of Kivy etc. bandwagon, and move to a browser, which would simplify a lot of things, particularly with respect to system monitoring while away from home via the internet.

So, I started leaning Nodejs, which begat getting a firmer knowledge in Javascript.  Then backtracking to HTML, then CSS - none of which I needed in my professional life before; well, OK, I did some stuff, but barely anything.  Then came Jade, and document databases, and Nedb.  Then somewhere Express.  I stayed away from CSS, Express, Jade for a while, because I was concerned about the Beaglebone being able to host all of this, but it turned out not to be a problem.

So, if you were like me, experienced programmer, but needing web based knowledge, then I was suggest the following learning path, in this order:

  1. HTML
  2. CSS
  3. Javascript
  4. Nodejs
  5. Express
  6. Jade

So, my redesign!

  • Uses the Beaglebone Black.  I'm going to also develop on the Raspberry PI 2; will update with that info.
  • Hosts a web server via Nodejs
  • Uses the Google Chrome browser.  Others may work, but I'm not testing or programming to those other platforms.
  • Provides dynamic web page security updates.
  • Displays current weather information while no security work or events taking place.

Since the base display is weather displays, and I needed somewhere to start, I first programmed the weather display system.  The design for this is:

  • Runs on Beaglebone
  • Hosts a web server via Nodejs
  • Uses the Google Chrome browser.
  • Provides dynamic web page weather updates.
  • Obtains live data from for my local, every 5 minutes.
  • Obtains static radar jpg images from and wunderground.
  • Displays a digital clock, data from the Beaglebone pushed to web page.  If the network drops, the Beaglebone freezes, the server freezes, the browser freezes - then the seconds no longer update.  In the future, the time will also change color, and maybe an alarm is generated.
  • Will switch to security mode on work or event.
The weather system is functional.  I'm currently refactoring the code and adding a few new features.

When those updates are complete, I will publish.


Nodejs: Passing values from Express to jade to javascript!

Passing values from Express to Jade to Javascript

Note: jade version 1.11.0
Today's date: 2/17/16
Note: assumes you are somewhat familiar with the technologies mentioned (nodejs, jade, express, javascript, html)

I've been hard at work on my security system, but came across an issue that took several hours to resolve.  I'm a very experienced programmer (C, C##, Java, Python, assembly, Fortran, Basic, etc), but almost all of that development has been done on back-end stuff; not much GUI front end stuff, no HTML stuff.  So, I'm somewhat weak on the front-end stuff; just now leaning nodejs, jade, express, javascript, html!

The security system I'm designing and building requires a lot of front-end stuff; it's showing the status via sms text messages and the browser.  This means the architecture is going to make use of:

  • Nodejs (note this is now the correct spelling for this product)
  • Jade (used with Nodejs)
  • Express (used with Nodejs)
  • Javascript
  • HTML

Instead of having an image of the current security system on display in the browser all of the time, I decided to have the current weather shown, along with the current time.  Weather in the Southeastern US can be quite volatile, so I have kept a radar image up on an old laptop in our living room for years, so weather is important to me to keep aware of.

The idea is the weather will be shown until either I select to view/work on the security system, or a security event occurs, in which cases the browser will display the appropriate security screen.  As part of the weather, I'm getting current weather information from the API.  For items such as radar images, I'm looping through some current jpg files that are offered from and

Now - the problem I was encountering.

In looping through the various web pages, I have to have a delay between pages in seconds.  I want this value to be passed in at the time the application is started, for the default value.  Later, I intend to add a change that will let me interactively change the delay time.

The current architecture, using Nodejs and Express, renders a loopingPages.jade file.  I'm passing the the DELAY value obtained at startup via process.env.DELAY in app.js, where it stores the value, before rendering the looping pages.  So, the DELAY value is passed from the startup command line to the app.js (the server), then to the jade rendered page via:

     app.get('/loopingPages', function(req, res) {
          res.render('loopingPages', {delay:DELAY}

The jade file loopingPages.jade includes a script file.  So, to be clear, the value that is originating from app.js server (using Express), needs to be passed to the rendering jade file loopingPages.jade, and this file includes a javascript file loopingPages.js, where the DELAY is actually used.

Well, I couldn't get it to work.  I could get the DELAY value from the environment variable passed at startup using the 'process.env.DELAY' term, but I could not get it to propagate properly.

After a lot of searching on the internet, I was unable to find an example that matched the one I needed, and most were old.  Seems this was an exercise in futility and esoteric programming!

But, I finally got it to work!

Below is a simplified version, which I was able to get to work.  It assumes you have created a fresh nodejs Express architecture for using this, which creates the proper directory structure and contents that I'll add to.  All directory locations are relative to your base directory for the application where app.js is located.

1. Modify routes/index.js to add name:'Banjo'
        res.render('index', {title: 'Express', name: 'Banjo' });

2. Modify views/index.jade to add p My name is index.jade #{name}
It should look like this:
     h1= title
     p Welcome to index.jade #{title}
     p My name is index.jade #{name}

The #{name} will show the name value passed from the app.js on the web page.  The #{title} was already available from the initial build.

3. At the bottom of index.jade (above), add the following inline script and script src:
          var theName = "#{name}"
          var theTitle = "#{title}"
          console.log("name passed in to index.jade is " + theName)
          console.log("title passed in to index.jade is " + theTitle)

Note the new file indexInclude.js which you will create next.

4.  Using your programming editor, create the file
It should have the following content:
     console.log("This is from indexInclude.js");
     console.log("+++++++++++FINAL: IF Banjo SHOWS THEN SUCCESS!+++++++");
     console.log("indexInclude.js theName is " + theName);

5. Run the app.js server
6. Open your browser to your localhost:port needed for nodejs
7. Confirm you see 'Banjo' printed on the page
8. Right-click on the page, then do 'inspect element' or similar for your browser.
9. Select 'console' tab
10. The console.log item should show text that includes the above (step 4) Banjo.

I hope this has helped you!