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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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!
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:
Based on my needs, here is what I found and I’ve added some additional general points:
I really have no idea why these things are so popular…
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: