Every time you start your project one of the most important things is to thinking about what electronic components you will choose. There might be a series of questions you might have to answer for yourself. Lets say you will construct some robotic or other sensor related system based on microcontroller. Then questions might be as follows:
What type of microcontroller to use for your project?
What type of clock generator to use?
What type of power source to use?
What type of sensors will be used for gathering of information?
What will be output devices (motors, displays)?
Will you need some kind of memory excluding internal microcontroller memory?
Can all required components be found without problems?
And the last question you will need to ask yourself is:
Can other amateurs repeat your project on your component base? Lets say you will make your system using some exotic electronic components or programming environment then it can be difficult to replicate your system. Of course if you are making it only for your needs and you are not going to document it, then there is no problem.
But in other situations first thing in your project is accessibility of electronic components. Of course some components may obsolete or reach end of line like Atmel’s AT90S2313 microcontrollers.
If your project isn’t very professional then it is better to use well known electronic components like:
diodes 1N4001, 1N4192;
transistors 2N3904, BC547/BC557;
field transistors IRF510/IRF9510;
ceramic resonators ECS;
logic components TTL series 74LS;
voltage stabilizers 78(L)XX;
Usually there is no problems with resistors and capacitors. Sometimes it is hard to find tantalum capacitors for filtering of IC’s power supply but they can be substituted by ceramic ones.
The key question is a choice of microcontroller. It has to fit all required characteristics. Choice may depend on previous experience. For instance if you are used to use ATMEL Atmega series of microcontrollers then you will probably will chose on of those wit desired properties. And check manufacturer product table to find out is this microcontroller in production or in end of line…