1. The Need Specification

2. References Adapted from:
Design for Electrical and Computer Engineers, first edition, by Ralph M. Ford and Chris S. Coulston
Excerpts from the book “Engineering Design, a Project Based Introduction”, second edition by Clive I. Dym and Patrick Little. John Wiley and Sons, Inc. ISBN

3. What are Specifications?

4. Definitions
Specification A detailed and exact statement of particulars, a statement fully describing something to be built.
American Heritage Dictionary
Specifications A detailed, exact statement of particulars, especially a statement prescribing materials, dimensions, and quality of work for something to be built, installed, or manufactured.
answers.com
Specifications may indicate as well acceptance criteria (very important).

5. What to Specify?

6. What to Specify?
The Objectives and The Problem Statement resulting from the attributes in the Need Analysis
Short statements that describe the need in the language of the client (or the user) like:
“The amplifier should have good sound quality” resulting from:
Interview, survey, brainstorming
Translate the Objectives into Engineering Language and attach numbers to them
The system should have Low Total Harmonic Distortion
Specification: THD < 1%
Constraining the Objectives

7. Translating the Need into Engineering Language and Technical Specifications
Performance
Performance specifications identify performance levels that signify the achieved desired functional behavior.
The system should detect 90% of all human faces in an image.
The amplifier will have a total harmonic distortion less than 1%.

8. Who defines the specifications?

9. Who defines the specifications?
The Client and the Team
After the Need Analysis, requires
One or more additional meetings

10. Objectives and Problem Statement Properties
Abstract: What the system will do, not how it will be implemented
Verifiable: There should be a way to measure or demonstrate that the objectives met in the final realization
Unambiguous: Each requirement should have a single unambiguous meaning and be stated with short complete sentences.
Traceable: Each Engineering requirement should be traceable to client, users or designers

11. Objectives and Problem Statement Properties
Good Example
The robot must move forward fast, with the ability to accelerate from standstill to the average speed in under one second.
Bad Example
The robot uses IR sensors to sense its external environment and navigate autonomously controlled by a Raspberry Pi
Fast always indicates short time
IR sensors and Raspberry Pi are implementations
Autonomous cannot be associated with single meaning

12. Validation VS. Verification

13. Validation
Validation = Are we building the right product? (Objectives)
Verification = Are we building the product correctly? (Specifications)

14. Technical specification
A complete list of the technical details for a given system, e.g., accuracy, speed, dimensions, etc.
List as a table at the end of section

15. One Example

16. Car Audio Amp The Audio Amplifier should have excellent sound quality.
Objectives
Specification
Justification
The Audio Amplifier should have excellent sound quality.
The Audio Amplifier should have high output power.
The Audio Amplifier should be easy to install.
The Audio Amplifier should have low cost.
The Audio Amplifier should be efficient.

17. Car Audio Amp THD Output Power
Objectives
Specification
Justification
THD
Output Power
The Audio Amplifier should have excellent sound quality.
The Audio Amplifier should have high output power.
The Audio Amplifier should be easy to install.
The Audio Amplifier should have low cost.
The Audio Amplifier should be efficient.
Translate Objectives into Engineering Language. i.e., Sound Quality = Total Harmonic Distortion (THD)

18. Car Audio Amp The Audio Amplifier should have excellent sound quality.
Objectives
Specification
Justification 1
The total harmonic distortion should be <0.1%.
Based upon competitive benchmarking and existing amplifier technology. Class A, B, and AB amplifiers are able to obtain this level of THD. 2
Should be able to sustain an output power that averages  35 watts with a peak value of  70 watts.
This power range provides more than adequate sound throughout the automobile compartment. It is a sustainable output power for projected amplifier complexity.
The Audio Amplifier should have excellent sound quality.
The Audio Amplifier should have high output power.
The Audio Amplifier should be easy to install.
The Audio Amplifier should have low cost.
The Audio Amplifier should be efficient.
Determine the specs and justify them.

20. Probably most of user will not distinguish between .1% and .01% THD
Or Probably 200 W will represent a hazard for users in a car
Probably nobody will buy a 10% THD
Or one that delivers a max of 5W

21. How to determine the values: Trade-Off
THD
Power
Usually the better the spec the more expensive to produce

22. How to determine the values: Trade-Off
Power
Probably improving the THD spec may require to impair a little the power spec to keep price reasonable
THD
THD
Usually the better the spec the more expensive to produce
Power

23. How to determine the values:
Competitive Benchmarks
Cost
Perception

24. Competitive Benchmarks
Apex Audio
Monster Amps
Our Design
THD
0.05%
0.15%
0.1%
Power
30W
50W
35W
Efficiency
70%
30%
40%
Cost
$250
$120
$100 24

25. Car Audio Amp. Objectives Specification Justification 1
The total harmonic distortion should be <0.1%.
Based upon competitive benchmarking and existing amplifier technology. Class A, B, and AB amplifiers are able to obtain this level of THD. 2
Should be able to sustain an output power that averages  35 watts with a peak value of  70 watts.
This power range provides more than adequate sound throughout the automobile compartment. It is a sustainable output power for projected amplifier complexity. 5
Should have an efficiency () >40 %.
Achievable with several different classes of power amplifiers. 3
Average installation time for the power and audio connections should not exceed 5 minutes.
Past trials using standard audio and power jacks demonstrate that this is a reasonable installation time.

26. Car Audio Amp. 3,4 The dimensions should not exceed 6” x 8”x 3”.
Fits under a typical car seat. Prior models and estimates show that all components should fit within this package size. 4
Production cost should not exceed $100.
This is based upon competitive market analysis and previous system designs.
Objectives
The Audio Amplifier should have excellent sound quality.
The Audio Amplifier should have high output power.
The Audio Amplifier should be easy to install.
The Audio Amplifier should have low cost.
The Audio Amplifier should be efficient.

27. Assumptions and Limitations
Assumption – The result of any project decision, which is required to complete the project definition, but is not a physical limit (minimum or maximum) that was imposed by the client, the technology used, or a physical law. Assumptions are the result of decisions that can be made by the team and affect the end-product design and implementation. Examples would include:
The maximum number of simultaneous users of a computer program, or
The maximum number of books to be stored on the shelves of a bookcase.
Limitation – The result of any project decision, which is required to complete the project definition, but is a physical limit (minimum or maximum) that was imposed by the technology used, or a physical law. Limitations are the result of things over which the team has no control, but must consider in its end-product design and implementation. Examples would include:
The maximum weight or size of user that would fit in the product without damaging it.
The maximum power consumption, or (Limited by size of PS or Breakers)
The maximum speed of the end product (limited by the type of gates or microcontroller)

28. Assumptions and Limitations
We care about technical Assumptions and Limitations. Please do not list in your assumptions things like:
The user has technical background or
The weather will be fairly good
Do not confuse constraints with limitations

29. Operating environment
For any end product other than simply a calculation, it is essential to know the environment to which the end product will be exposed or experience.
For example, will the end product be exposed to dusty conditions, extreme temperatures, or rain or other weather elements?
Is the end product likely to be dropped or thrown?
This information is necessary in order to design an end product that can withstand the hazards to which it is expected to be exposed. This element shall be at least one paragraph in length.

30. Intended user(s) and intended use(s).
Knowing the characteristics of the end users makes it much easier to design an end product that will be accepted and used.
The expected end uses are equally important. This description should include what uses are expected as well as what uses are not to be considered

31. Specifications THD < 0.1%. Prms 35W Ppeak 70 W ƞ > 40 %
Average installation time < 5 minutes
Dimension 6” x 8”x 3”
Cost < $100
Input Voltage 12V (Operating Environment)
Temperature in Operation 0 < T < 50C (Operating Environment)
12 hour operation when car is off (limitation)
Human Interface: Touch Screen (Assumption)

32. &
Questions
Answers