It is becoming increasingly difficult to buy electronic components on the high street, as more and more of the bricks and mortar retailers that sell a wide range of electronic components shut down. This means that those who are interested in more complex hobby projects, and those that work extensively with electronics and like to do ad-hoc prototyping are forced to look online for components.
There are numerous places that you can buy components online, from auction and independent sellers on Amazon and eBay, to sites such as Jameco.com, Sparkfun.com and Digikey.com. The challenge is figuring out which components are worth buying, and exactly what you need. Indeed, for the novice and the intermediate hobbyist, one of the best things about buying from a regular store is that you could go into the store and ask them for advice if necessary. It’s harder to get support online and it can sometimes feel like you’re taking a shot in the dark when you’re picking out something like a resistor or capacitor, let alone a more complex IC.
Where to Buy
If you’re not sure where to buy, then you might want to start your shopping trip at Bitsbox, or Sparkfun. These are hobby stores that have most of the standard components that you are likely to want for a beginner project. You can get the part number from one of those stores and then shop around to see if there is anywhere that has a sale on or that offers fast/free delivery to your area. You don’t have to buy direct from those stores if the price isn’t right.
If you need something more obscure than the items in the hobby store catalogues, then look to DigiKey. They have the best list of electronic components, but it can be a little intimidating to trawl through their catalog as a hobbyist. It’s pretty much essential to use it if you’re working on a more complex project though. Alternatively, if you’re doing highly specialist work in, say, a medical or military niche you might need to communicate with the manufacturer of the boards you’re working with to get the parts that you need for the job.
Tips for Choosing Components
If you’re working from a schematic and it gives you a vague list of components, then narrowing down what you actually need in the store might be a little difficult. Let’s say you need a resistor rated at a certain number of Ohms. OK, that should be easy enough to buy, but when you’re browsing the catalog you find that there are so many different types of resistor to choose from.
What’s better, metal or carbon film? Do you want a foil resistor or a wire wound? Why should you care?
Well, to an extent if you’re making something basic for a school science exhibit it might not matter at all, except for price. But if you’re making a more complicated project then it will matter. Some resistors are accurate, some are intended for high power situations. Some are designed to be able to withstand high temperatures, and some are good for high speed applications, or for measurement, or for low noise. Some are just intended to be as cheap as possible while still getting the job done.
For a simple project, you will most likely be able to get away with using the cheapest resistor you can find that has the correct Ohm rating, and a power rating that is roughly twice the power rating for the job. There are a few scenarios when you would want to choose a non-standard resistor, though, such as:
– Audio circuits that are noise-sensitive
– RC circuits
– Measurement circuits where accuracy is vital
– High power circuits
– High speed circuits
If you are working from a schematic that doesn’t give a power rating for the resistor, then you can try to calculate it yourself. If you can’t do that, then you can try a 1/4W resistor, since that’s the most common type. If you find that this fails quite quickly, then swap it out for a higher wattage rating.
Capacitors are another thing that confuse a lot of beginners when they are trying to buy components online. The two main types of capacitor are polarized ones and non-polarized ones. Polarized capacitors have two sides, one positive and one negative. They must be aligned correctly in the circuit. A non-polarized capacitor is not like this and can be placed with the pins either way around.
You can tell whether or not you need a polarized capacitor or not by looking at the circuit diagram. If you need a polarized capacitor then the capacitor symbol will have a + on one side to indicate where the positive pin should go.
Once you know whether you need a polarized or non-polarized capacitor, the next question is whether to get an aluminum capacitor or a tantalum capacitor. Both of these may be labelled as being electrolytic, which indicates that they are polarized.
Aluminum capacitors are the most common, and also the most affordable. They are a good choice unless you have a specific reason to purchase tantalum ones. Tantalum capacitors are smaller and more durable, so are often used where space is at a premium or if the application will require components that can tolerate wide temperature ranges.
Non-polarized capacitors can be ceramic, or film capped. Ceramic caps are small, and they don’t cost a lot, so they are a popular choice. Film caps, however, are a bit more expensive but they are useful for more demanding applications where you might want low tolerance, improved reliability, or better toleration of high temperatures. There are other varieties of capacitor, but they are beyond the scope of a general guide.
If you are looking for other, more specialist components, then it’s a good idea to download and read the data sheet for the component that you are considering buying from WWW.DIRECTICS.COM and compare it to the schematics. Usually you can figure out what exactly you need with some basic research.