Choosing the product and regulatory requirements
Among an energy meter, an irrigation controller and a medical monitor, the decision matrix picks the irrigation controller if feasibility and regulations carry weight, and the monitor if only the market and the team’s interest do. The weights are also a decision.
01From the idea to the need
The final project integrates the degree into a product or system that solves a real problem. Ideas can come from a need observed in a company, a hospital, a cooperative or a municipality, from a new technology that opens up a possibility, or from improving an existing product. Before thinking about circuits, it pays to answer: what problem is being solved, for whom, and how is it solved today? Talking to the future users, observing how they work and studying the products that already exist avoids designing something nobody needs.
02Requirements and specification
The need is translated into requirements: functional ones say what the product must do —measure the current, notify through the phone, log a year of data—; non-functional ones, how it does it —accuracy, battery life, operating temperature, size, cost, service life, ease of use—. The specification makes them quantitative and verifiable: not “low power consumption”, but “two years on two AA batteries”; not “accurate”, but “±1 % between 10 and 100 A”. Every number in the specification must be verifiable with a test at the end of the project.
03Comparing alternatives
When there are several ideas, or several ways of solving one, a weighted decision matrix organizes the discussion: the criteria are chosen, each is given a weight according to its importance, each alternative is rated on each criterion and the products are added up:
Three ideas rated from 1 to 5 on five criteria (higher is more favorable): A, household energy meter with wireless connection (4, 4, 4, 3, 3); B, irrigation controller with soil moisture sensors (3, 5, 5, 5, 4); C, portable vital signs monitor (5, 3, 2, 1, 5). The weights are chosen with the controls.
04Regulatory requirements
An electronic product that is sold has to comply with standards, and it pays to know them from the start because they constrain the design: insulation distances, the mains filter, the enclosure, the materials. The corresponding tests were covered in tests and standards.
| Aspect | Reference standards and bodies |
|---|---|
| Electrical safety | IEC 62368-1 for audio, video and information technology equipment; IEC 61010-1 for measuring and laboratory equipment |
| Electromagnetic compatibility | Emissions according to the CISPR family and immunity according to the IEC 61000-4 series |
| Radio equipment | Type approval from ENACOM (the national communications regulator) in Argentina |
| Medical equipment | IEC 60601 series and registration with ANMAT (the national drug and medical device regulator) |
| Environmental | Restriction of hazardous substances (RoHS) and electronic waste management, depending on the market |
In Argentina there is also a mandatory safety certification regime for electrical products. Standards and resolutions change: the current text has to be consulted on InfoLEG and from the relevant bodies before fixing the specification.
05In the laboratory
Interview three potential users of the chosen product and rewrite the requirements with what they said.
Convert each requirement into a quantitative specification and write, next to it, the test that would verify it.
List the standards the product should comply with and the tests they require.
06Common mistakes
- Starting with the technical solution. First the need and the user; then the circuit.
- Writing requirements that cannot be verified. “Rugged” or “intuitive” cannot be tested.
- Discovering the standards at the end. They can force a redesign of the enclosure or the power supply.
- Choosing a scope that is too large. A finished and tested project is worth more than an ambitious half-done one.
07Self-assessment
With the initial weights of the lab, what score does each idea get?
A 3.71, B 4.29 and C 3.29: the irrigation controller wins.
What weights make the vital signs monitor win?
For example, market 5, feasibility 1, cost 1, regulations 0 and interest 5: C gets 4.58.
What is the difference between a functional and a non-functional requirement?
The functional one says what the product does; the non-functional one, how and under what constraints it does it.
Which body approves radio equipment in Argentina?
ENACOM.
08Further reading
- Karl T. Ulrich and Steven D. Eppinger. Product Design and Development. McGraw-Hill. (Spanish edition: “Diseño y desarrollo de productos”.) Customer needs, specifications and concept selection.
- Tim Williams. EMC for Product Designers. 5th ed., Newnes, 2016. Compatibility standards and how to design to meet them.
- Jack Ganssle. The Art of Designing Embedded Systems. 2nd ed., Newnes, 2008. Practical advice for taking an embedded system from the idea to the product.