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Datasheets are your friend
Before buying components, you should read the datasheet. A datasheet for an electronic component includes a wealth of information, such as:
- Physical dimensions for mounting and PCB layout
- Electrical requirements
- Details for proper usage
A datasheet can range from a single page to hundreds. For example, many modern Intel CPUs have 2-volume datasheets that total well over 100 pages.
Datasheets are normally in PDF format. (In the old days you would call the manufacturer and they would send you actual paper!) If it doesn't actually say "datasheet", check carefully - it may just be marketing material without the specific details you really need. Datasheets also change over time - a revised version might cover fixes to CPU flaws or improved tolerances or other changes.
Even if you think you know exactly what component you want to use, get the datasheet. There may be relatively subtle distinctions between components - e.g., voltage requirements or current usage - that can make one version of a component far superior to another for a particular application. For example, current usage may not matter much for a device running on mains power, but for a field sensor collecting data on battery/solar power 24/7, every milliwatt counts!
Datasheets are available in a variety of locations. The best sources are usually the manufacturer or a major distributor, but some are available through Wikipedia and other sources. Here are two examples:
Where to Purchase Components
Once you have figured out what components you want to use, you need to figure out where to get them. In the olden days, Radio Shack was the go-to place for hobbyists. But Radio Shack is mostly gone, and the universe of electronic components is far larger than it was 40 years ago. Your natural inclination may be to go to Amazon. But beware. Components purchased from Amazon can vary greatly in quality and may even be counterfeit. Be particularly wary of anything that says "Fulfilled by Amazon". That is a code phrase for "Someone else is importing this item and shipping it via Amazon, but Amazon is not really guaranteeing what is in the box". In addition, for small components, Prime-includes-shipping can bump up the price. You also may find a 50-cent item listed as $0.01 + $3.99 shipping, where if you bought it from a regular vendor it would really be a $0.50 "true cost". Buyer beware.
Most component manufacturers will not sell directly to small companies & hobbyists. A number of reputable distributors fill the gap. In addition to handling small orders, these distributors allow you to order items from multiple manufacturers at one time, provide access to datasheets and additional information, easily search through products (unlike Amazon where LED diodes get jumbled together with LED strip lights and LED headlights and incandescent bulb replacements) and find what you need. Some examples (as of 2020) are:
Keep in mind that not all distributors ship (at least at an acceptable price) to all locations and there are minimum order requirements and other constraints. But overall, a dedicated component distributor will provide more & better options than a general store such as Amazon.
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Any electronic component or module you buy for a project or design should have a data sheet. By data sheet I mean a portable document format (PDF or equivalent) like this: -
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Do not assume that the product will be OK based on marketing/sales claims without researching the fine detail in the data sheet. This is why you need a data sheet so, do your homework and ensure that what you think you need is matched by the technical details in the data sheet. Make sure you have the latest data sheet (see 3 below).
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The data sheet is sometimes wrong so, if something appears not to make sense, double check that you have the latest issue of data sheet and, if in doubt about some parameter or other, you can always raise a question on this site to gain clarity.
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Earlier revision data sheets are usually available and so, if the manufacturer updates it, this can be traced back to the point where the change was made. Always save the data sheet in your design file when you use a new part. On the other hand, web-based specifications have no historical traceability and can lead to confusion and mistrust should things go wrong. This can make you appear stupid or careless and, won't provide the evidence that can cover you should there be customer dissatisfaction or legal problems.
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The manufacturer of the part should be reputable but, as we know, new part manufacturers entering the market may not have gained a significant reputation. So, this may be hard to establish and, you have to be cautious. A lot of confidence can be gained by reading and understanding the data sheet of the part.
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The supplier/shipper must be reputable for the type of goods they are handling (namely electronic parts) and, they should provide links to the manufacturer's data sheet (1). How do you know that some unmentionable supplier hasn't mishandled the goods and damaged them? I'm thinking ESD and water damage here but, there are probably other ways "unseen" damage can occur.
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Watch out for fake parts - if the price seems too good to be true then maybe consider that the parts might be fake or possibly failed items underhandedly acquired by some disreputable supplier
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Decide what you need to buy - don't assume that any old resistor, capacitor, transistor or op-amp is going to work - think about what your final expectations are and, where things can go wrong (such as drift or basic output inaccuracies). You can't expect a supplier to be held responsible for you choosing a part that you haven't thought through sufficiently. This is what design is about - it's not about guessing that this or that will do so, do your homework (or pay the cost).
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If you buy from a source selling unbranded goods you are taking a risk and, quite possibly, you will pay more (due to you wasting your own time) in the longer run so, how much do you value your time?
I'll probably think of a few more things to add as time passes by.
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