What Makes Part Selection Difficult?

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There are several competing factors that guide part choice.  In this chapter, you will learn some of the things engineers look for when choosing a part for a design.

1. How to Choose a Part

Electrical Engineering is part science and part art.  The science is in the circuit design -- component values are calculated, not guessed.  The art is in balancing all of the competing requirements for a job:  Engineers often have to balance performance, project cost, timelines, link budgets, power budgets, part availability, and more.

Parts have to be suitable for the job at hand.  And determining the suitableness of a part for a specific job is harder in some cases and easier in others.

For example -- if you need a 470 Ω resistor, it's a pretty simple matter to find one, and the limiting factor is usually just cost.  But if you need a microcontroller that has 5 USART busses, capacitive touch, and operates off of ~1 µA in sleep mode, you are going to have to read (and understand) a lot of datasheets from a lot of manufacturers -- make sure you have access to the software toolchain needed to program the microcontroller, and then ensure that the cost fits within your budgetary requirements.

We will learn how to read a datasheet while we are waiting for our boards to be manufactured.  But for now, we've done the hard part and selected all of the parts on the BOM for you.

Hardway Hughes"All jobs are different.  If all you make are prototypes, the cost of parts for a single design isn't all that important.  But there are always constraints put on projects, whether it's manufacturability, reliability, assembly, etc...  Engineers refer to this as 'Design for X' (DFX), where 'X' is manufacturability, assembly, cost, reliability, etc..."