Designing an electronic circuit starts with boxes whose insides are ignored
Before an engineer picks a single resistor, a new circuit usually exists as a diagram of empty boxes. Each box states a job, such as amplify, filter or power, with no thought yet about what goes inside. This black-box approach lets a daunting design be split into smaller puzzles that a team can share out.
The work begins with a specification describing what the finished circuit must do, never how. It lists the signals coming in and going out, the power available and the most it may draw, plus physical demands such as size, weight, temperature range, moisture resistance and tolerance of vibration or acceleration. As the design takes shape, engineers often return to that document, tightening requirements and adding tests, though any change that clashes with the customer's original wishes normally needs their approval.
Poor communication at this stage invites design creep, which ranges from a circuit that does more than anyone needed to one that does the wrong thing. A common rule of thumb is to keep options open as long as possible, because removing spare elements later is easier than squeezing new ones in.
From the block diagram, each box is fleshed out with increasing electrical detail, often backed by research or mathematical modelling. If one block turns out to be impossible within its limits, neighbouring blocks may be redesigned to compensate. Only at the end are individual components chosen and laid out, typically as artwork for a printed circuit board or chip. This step eats time because the choices are vast, and a calculated value is useless if nobody sells that part, so designers lean on what is sometimes called catalogue engineering, picking standard parts off the shelf.
Two checks follow. Verification walks through the design on paper and in large computer simulations to confirm it meets the specification, often uncovering problems that force substantial rework. Testing is its physical twin: building prototypes and measuring whether they behave. Designing usually costs far more than making each unit. In the European Union, the paperwork typically ends with a CE declaration naming the person responsible for compliance.
Source: Circuit design
