Electronics, Photography, Gadgets

Month: March 2010 (page 1 of 2)

Ohm’s Law

This video from Make Magazine is a great introduction to ohm’s law and a good way of bringing some of the science behind electrical circuits to kids and adults alike.


A First Simple PICAXE Microcontroller Project

Some of my son’s other interests include traffic lights (or stop lights), boom barriers, automatic doors and control panels of any kind. The first microcontroller project we decided to build was a traffic light system including a pedestrian crossing. The microcontroller kit I decided to use for this was the PICAXE-20M Starter Pack (USB) which uses a PICAXE 20M with 8 input pins, 8 output pins, 220 lines of program memory and supports interrupts, digital temperature sensors, radio-control servos, keyboard input, user defined musical tunes, infra-red transmission and reception, an 8/10 bit ADC option, pwm motor control and input pulse counting. The device is programmed via the supplied USB cable. It is a surprisingly sophisticated chip for 2,35 euros. Below is an image of the 20M connected to a small breadboard with three LEDs (one red, one yellow, one green) and 330 ohm resistors.

PICAXE 20M Traffic Light Project

In the circuit above, we connected output pin1 to a 330 ohm resistor and then a red LED, output pin2 to a 330 ohm resistor and then a yellow LED and finally output pin3 to a 330 ohm resistor and then a green LED. To program the PICAXE, you will need a copy of the MacAXEPad for the Apple Mac or AXEPad for the PC which is available at the PICAXE software download page. There is also a comprehensive set of manuals online which describe how to develop code for the PICAXE in BASIC. The basic program below controls the traffic light and is my son’s first ever piece of code. :-)

high 1
pause 3000
high 2
pause 1000
low 1
low 2
high 3
pause 3000
low 3
high 2
pause 1000
low 2
goto tlight

Alarm 2.0 and Microcontrollers

The next projects we have been working on and will be described in later posts are much more sophisticated than the previous alarm system. The projects include: building logic gates such as AND, NAND and OR out of NPN transistors, a four bit adder out of logic gates which in turn are built from NPN transistors, a 4 bit counter from J-K Flip-Flops, a new version of our alarm system using 555 timers, logic gates, diodes and a keypad to activate and de-active the alarm and finally, a traffic light system using a PICAXE microcontroller and logic gates. If you would like to find out more about these components and electronics in general, I can highly recommend Make: Electronics by Charles Platt.

Make: Electronics

If you would prefer an online source of information, I can also recommend doctronics which has some great guides and projects with useful circuit diagrams in breadboard format. Take a look at the doctronics biscuit tin alarm for a fun project.

From Breadboard to Perforated Board

The next phase in the development of our first alarm system was to move the components from the breadboard we had been using for prototyping to a perforated board on which we could solder the components and install it in my son’s room. To do this, you will first need to learn how to solder and there are some great online soldering tutorials such as the one below.


I personally chose a 15 watt soldering iron as I will only be using it to solder electronic components and the lower power should help protect the components from being damaged through exposure to too much heat. I recommend that you also purchase a vacuum de-soldering tool and a decent stand. What I have also found important is a third hand such as the one pictured below. This is a great tool for holding your board while soldering components onto it.

The Indispensable Third Hand

After a few minutes of practice, we were able to construct the simple alarm circuit described in a previous post onto a perforated board with little difficulty. The final result can be seen below.

Simple Alarm Circuit on Perforated Board


Editing PDF Files For The Kindle DX

In my previous post on the Kindle DX I mentioned two small issues with PDF files: PDF files with large borders and PDF files with restrictions. The Kindle DX automatically removes large borders from PDF files which makes the size of the text larger and easier to read. When, however, the border has something in it like a page number, the kindle does not remove the border as it contains something. An example of this is shown in the following screenshot.

Example PDF With Large Borders

The solution to this problem is to trim the unwanted borders and to do this I use an application for the Mac called PDFPen, which you can get here, from Smile on my mac. Not only can this application trim the borders from single pages or entire documents, but it can also merge PDF files or set the metadata in a PDF file so that the correct author is displayed in the Kindle’s home screen.

PDFPen Trimming a PDF

The second slight annoyance are PDF files with restrictions such as the inability to print or save the document. The problem is not being unable to print or save but the fact that the Kindle has problems with the metadata contained within these files. This means that the author name in not displayed or, in some rare cases, a collection of random symbols is displayed in its place. Annoying but not a big deal.

Our First Alarm Project

The project my son decided we should work on is an alarm system for his room. The first alarm we built is based on the lessons that we learnt using the conrad starter kit. It is based on the same components – a 9v battery, resistors, LEDs and an NPN transistor. The circuit can be seen in the image below.

Simple Alarm Circuit

The only components I added are a piezo buzzer, marked as buzzer in the circuit diagram, which you can buy for about 1 euro at most electronics retailers, and two switches marked as on/off and door in the diagram. For the on/off switch we used a lock switch which mean that the alarm can only be turned on or off with a key. For the door switch we used two power strips with multi.core wire stuck to them and then covered in aluminum foil – when the door opens, the contact is broken and the alarm is activated. The description for the circuit is below – give it a try! Please note that in the diagram I used an LED symbol as Circuit Simulator doesn’t have a buzzer component. The code for the circuit is listed below. Just copy and import the code into the free Java Circuit Simulator to get a feeling for the circuit.

$ 1 5.0E-6 10.20027730826997 50 5.0 50
v 368 368 368 272 0 0 40.0 9.0 0.0 0.0 0.5
r 368 272 368 208 0 330.0
162 512 208 512 288 1 2.1024259 0.0 1.0 0.0
s 368 208 512 208 0 0 false
w 512 208 608 208 0
162 608 288 608 368 1 2.1024259 1.0 0.0 0.0
w 608 448 512 448 0
w 512 448 368 448 0
w 368 448 368 368 0
s 512 288 512 448 0 1 false
w 608 208 688 208 0
w 688 208 768 208 0
t 688 288 768 288 0 1 -1.0853467247068087 0.6355071463035651 100.0
w 768 208 768 272 0
162 768 304 768 368 1 2.1024259 1.0 0.0 0.0
w 768 368 768 448 0
w 768 448 608 448 0
w 608 288 608 208 0
162 608 368 608 448 1 2.1024259 1.0 0.0 0.0
r 608 288 688 288 0 10000.0
x 413 237 469 241 0 18 on/off
x 788 347 847 351 0 18 buzzer
x 452 378 492 382 0 18 door

Amazing Java Circuit Simulation

Circuit Simulator is an amazing piece of free software. If you are in any way interested in electronics, download it from here and play around with it for an hour or so. I’m going to be using this application to publish the layouts for the cicuits we are working on in my future electronics related posts.

Circuit Simulator

If you want to see how the blinking LED circuit shown in the previous post works, paste the following into program using the import feature.

$ 1 5.0E-6 382.76258214399064 99 5.0 43
v 352 672 352 400 0 0 40.0 5.0 0.0 0.0 0.5
w 352 400 352 288 0
w 352 288 608 288 0
w 608 288 880 288 0
162 880 288 1008 288 1 2.1024259 1.0 0.0 0.0
r 1008 288 1008 320 0 500.0
w 1008 320 1008 336 0
w 1008 336 1120 336 0
w 1120 336 1120 832 0
w 1120 832 1104 832 0
r 1104 832 992 832 0 10000.0
w 992 832 816 832 0
t 528 400 608 400 0 1 -0.12632236495348304 0.5010407108474094 100.0
w 528 400 528 832 0
w 528 832 736 832 0
w 528 400 528 352 0
t 944 400 1008 400 0 1 0.5847909946260287 0.6273630758008925 100.0
w 1008 336 1008 352 0
w 1008 352 1008 384 0
w 1008 416 1008 672 0
w 800 352 800 400 0
w 800 400 944 400 0
w 1008 672 672 672 0
w 672 672 352 672 0
w 608 416 608 560 0
w 608 560 656 560 0
w 656 560 656 608 0
w 656 608 672 608 0
w 672 608 672 624 0
w 672 624 672 672 0
r 608 288 608 352 0 5000.0
w 608 352 608 384 0
r 608 352 528 352 0 5000.0
w 800 352 608 352 0
c 736 832 816 832 0 1.0E-5 0.21083170251411693

Electronics For Beginners

A new hobby that my son and I have taken up is Electronics. Not only is the topic interesting, but it is also educational for kids. The place that we started was with this starter kit from Conrad in Germany, but most electronics retailers such as Maplin Electronics in the U.K. and Maker Shed in the U.S. will have similar kits. The kit consists of assorted resistors, a 45uF capacitor, two NPN transistors and, fourLEDs, a small Bread Board, a length of single core wire and a battery connector. You’ll be amazed how much you can learn from a kit like this! In the picture below, you can see one of the circuits that we built using our first little kit – two NPN transistors connected to a 45uF capacitor and a few resistors that makes an LED flash on and off!

Blinking LED

Why Are Netbooks Good for Nothing?

After my last post, I thought that I should maybe qualify the reasons why I think notebooks are good for nothing. This is, of course, just my personal opinion and your mileage may vary. Firstly, I’ll point out my reason for buying a netbook in the first place:

  • My Netbook Use Case (reason for buying): I purchased a PIXACE microcontroller which I wanted to build and program with my son as part of our exploration into the world of electronics. Not being very experienced in electronics, I didn’t like the idea of connecting my Mac Book Pro or iMac to a 30 euro device which could explode or short circuit something. Answer: a cheap netbook to program the device, view circuit diagrams and component layouts, occasionally edit documents, watch videos, look at pictures and maybe surf the web now again (which I shouldn’t be doing of course – see my Kindle DX post).

Based on my needs, here is what I found and I’ve added some additional general points:

  • Viewing technical document and circuit layouts. The screen is too small! As netbooks screens typically only have 600 vertical pixels (1024*600), there is not enough screen real-estate.
  • Editing documents. The keyboard is too small to do anything half way serious – maybe my hands are too large.
  • Surfing the internet. It’s too slow. It is painfully slow – flash is a painful experience.
  • Watching videos. It’s kind of ok, but 720p won’t work. The sound quality is, again, kind of ok.
  • iTunes. Too slow. The user experience is awful, don’t do it.
  • Viewing images. It’s too slow. This may be a little unfair as I use raw format exclusively on a 12.3 megapixel camera. I also loaded on some jpegs and that was just about bearable.
  • Using it as an electronics stunt partner (something that wouldn’t break my heart if it broke when everything goes terribly wrong). Would work really well but, because of the price and limited usefulness, one of the cheap laptops I mention in the previous posts is a much better option – please note that two of these options only cost 10 euros more than the netbook I tried.

I really have no idea why these things are so popular…

Netbooks Aren’t Good At Anything

When Steve Jobs said this about Netbooks during his iPad keynote, I was a little skeptical of his claim. However, having used one for a week, I can only say that it is absolutely true. The experience is downright awful. They are slow, the display is too small, the keyboard is too small and they are really really slow. This experience was made on a netbook with an Intel Atom 1.6GHz N270 processor and the Intel 945GSE chipset. It also had 1GB of RAM, a 160GB HDD and a 10.1″ LED display running Windows 7 Starter. So, unless you need a really slow and small laptop with a terrible user experience, do yourself a very big favor and buy a cheap laptop such as one of the following and install Ubuntu on it:

  1. Acer Extensa 5235-901G16N (279 euros from Amazon) – dual core Intel Celeron M900 at 2.2GHz, 15.6″ wide screen display, 1GB RAM, 160GB HDD, WLAN 802.11 b/g/n, 3xUSB  Intel GMA 4500M, DVD.
  2. Fujitsu Esprimo Mobile V6535 (279 euros from Amazon) – dual core Intel Celeron M900 at 2.2GHz, 15.6″ wide screen display, 1GB RAM, 160GB HDD, WLAN 802.11 b/g, 4xUSB  Intel GMA 4500M, DVD.
  3. Asus X5DIJ-SX155L (369 euros from Amazon) – dual core Intel T4300 at 2.1GHz, 15.6″ wide screen display, 2GB RAM, 320GB HDD, WLAN 802.11 b/g/n, 4 x USB, Intel GMA 4500M, DVD.
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