Tips to Drafting an Effective Electronic Design Project Specification

While working on the product specification document it is very important to capture and present well-structured core information about the product, its function, properties, attributes, constraints and intended purpose. The document should be clear, concise and should outline all the information required by the design team and product team to successfully realize a functioning, marketable product.

Here are some pointers to keep in mind while drafting the electronic product specifications:

1. Purpose of the design/product


a. What is the purpose or idea behind the product? What is the problem is it solving?

b. This information will guide the design team to get a perspective and then, they can start thinking about how to design.

2. Intended User Personas


a. Identify and define the various user personas. Understand how each persona will interact with the product and define the requirements accordingly.

3. Targeted Geographical Markets


a. Identify the geographical markets the product will be marketed and sold in. Each country/region will have a different set of standards and regulations that the design/product will have to comply with.

4. Diagrams and Figures


a. Create a rough block diagram or Figure of the product to define different sub-blocks and keep refining as the discussion progresses. This is important to have a good high-level overview of the project.

5. Prerequisite Design Requirements


a. Regulatory Compliance/Certification requirements:


1. Understand and research the applicable Safety (UL/CSA/IEC), EMC/EMI (FCC/ISED/ EC EMC Directive) and Wireless radio operation (FCC/ISED/ EC Radio Equipment Directive) regulatory compliance regulations and Standards for the target countries. If in doubt, research similar competitive products literature to find out what regulations and standards will apply.

b. Target BOM cost


1. Target BOM cost gives the necessary direction to the design engineer for selecting various components, PCB technology to be used. As an example, a smaller PCB will cost less, mounting components on both sides of the PCB will cost more time and cost in the production but reduces the PCB size, etc. An off- the-shelf enclosure will be easier to source in the supply chain vs. custom enclosure that requires up-front NRE costs. As much as possible, all components, power supplies, wiring, enclosures, and any custom designed parts should be sourced from reputable suppliers and parts distributors, who have visibility of availability (OTS parts) and the necessary materials to provide a guaranteed cost and lead time.

c. Environmental Conditions


Provide the environmental conditions in which the product will operate:

1. What will be the operating & storage temperature range (i.e., -20 to +60 Deg. C)
2. What is the operating humidity range (i.e., 5 – 95 RH%)
3. The expected level of vibration the product will endure during transportation, handling, and installation in the field.
4. Will the product be primarily used indoor or an outdoor?
5. What is mounting style will be required (i.e., tabletop, wall, floor, etc.)
6. Is the environment hazardous (fumes, dust, gases, etc.)?
7. Is an IEC 60059 IPXX/NEMA YY water resistance/protection or dust resistant/dust-tight level required?
8. Will the product operate in a non-ideal environment (i.e., sea level, at elevated heights, etc.)?

The above points will dictate both the Hardware, wiring, connector, power supply designs, but also the mechanical design of the enclosure.



d. Production Volume


1. For high volume production, consider making a design that makes for efficient manufacturing: i.e., use of SMD components, fewer number of system components, fewer number of fasteners that require manual process.
2. Specify automated PCB Assembly inspection and functional testing equipment; these features will require additional HW and FW design to accomplish.

e. Product Lifecyle


1. Engineers should know the expected life of the product, as they will pay special attention to the critical component Lifecycle (active, mature, NR/ND or EOL) and alternatives. If the product will be available for 5+ years, it is important to consider long term availability while selecting various critical components. This will allow you to sell the product for 5 or more years and extend this product lifecycle to offer service and/or repairs.

f. Warranty:


1. If possible, think about the product warranty so that all project stakeholders can understand the reliability requirements. The design engineers will carefully select critical components when designing the Hardware circuits. Designing for a warranty of 1 year or 10 years will be entirely different.

6. Main Features


a. Hardware Design:
The Hardware design specification should provide detailed requirements related to various features as given in the block diagram, figures, or photos. These include:


1. Should be powered by an external AC/DC wall or desktop power source.
2. Should be powered by 5V DC input, via USB Type C Power Delivery (PD) source.
3. Should be powered with a secondary rechargeable Lithium-Ion/Lithium-Poly battery pack that will charged in X hours and provide Y hours of typical operation.
4. Should have Wi-Fi 5 (802.11 b/g/n/ac), Bluetooth / BLE 5.0, LoRa and/or 4G LTE-FDD Cat-4 cellular wireless connectivity.
5. Should have a backlit LCD/OLED display visible from a distance (specify).
6. Should have a simple User interface to configure via a keypad, or custom pushbutton configuration. (NOTE: If you have a preferred configuration, insert in the specification).
7. Should indicate the color and functionality when the operator visible LED(s) are operating.
8. Should have one serial (RS-232 or RS-485), one Ethernet (1 Gbps) and one HDMI/DisplayPort connection.
9. Should have X number of Analog, and Y number of Digital Inputs, all should be 3.3V/5V/12Vdc compatible.
10. Should have X number of electro-mechanical or Solid-State relays to control external equipment.
11. Should have suitable 32-bit ARM CORTEX-M33 MCU or 64-bit ARM CORTEX-A53 multi-core CPU that supports the required OS, and support key peripherals (I2S, I2C, SPI, UART, USART, USB 2.0/3.0) and has embedded core circuits (DMA, Flash memory, PWM driver, ADC, DAC, etc.).
12. The whole product should not consume more than X watts peak and Y watts typical (state the conditions for both peak and typical functionalities).

b. Hardware Protection Circuits:


1. State the I/O, Power supply and other required protections, such as: The DC input voltage should have over-voltage, over current, surge protection. All IO interfaces should have ESD protection and CM chokes.
2. Industrial RS232, RS-485, Ethernet I/Os should have Surge protection, voltage clamping and/or isolation based on the end user’s requirement document or industry standard.
3. Review possible failure modes in the field, to provide necessary protection to ensure the product functions for a longer period.
4. Use suitable EMI components and CSA certified/UL recognized isolation transformers, MOVs and TVS diodes for all input / output power sources and I/Os.
5. Note that Hardware design will be dictated by your stated environmental conditions, thermal cooling of higher power parts, and regulatory compliance requirements (Safety and EMC/EMI standards).

c. Firmware:


1. State the I/O, Power supply and other required protections, such as: The DC input voltage should have over-voltage, over current, surge protection. All IO interfaces should have ESD protection and CM chokes.
2. Industrial RS232, RS-485, Ethernet I/Os should have Surge protection, voltage clamping and/or isolation based on the end user’s requirement document or industry standard.
3. Review possible failure modes in the field, to provide necessary protection to ensure the product functions for a longer period.
4. Use suitable EMI components and CSA certified/UL recognized isolation transformers, MOVs and TVS diodes for all input / output power sources and I/Os.
5. Note that Hardware design will be dictated by your stated environmental conditions, thermal cooling of higher power parts, and regulatory compliance requirements (Safety and EMC/EMI standards).

d. Hardware Protection Circuits:


1. Create a high-level flowchart and discuss with your Firmware team what will be the high-level code execution plan.
2. Request proper FW code structure with modularity and reuse in mind, written in a common low-level language (C++, C#).
3. For an LCD/OLED displays, define the screen layout/Menus/colors.
4. For wired and wireless communication interface, define a clear command packet structure, desired Protocol (MQTT) and data interchange payload type (JSON).
5. If required, state if a RTOS will be needed, or if a higher functionality OS (LINUX based) will be needed.
6. Is power management critical, ensure that the Power ON, Power Off of various voltage rails is stated.
7. If cybersecurity and encryption is required, clearly state the standard version and/or key cryptographic protocol versions that are required for packet based wired and wireless data communications.

e. Firmware Field updates:


1. Due to tight design project timelines, it is not practical to test all field conditions for your product; this means you will need to fix a bug or provide a feature update to improve UX or add certain specific features (i.e., enable 3G UMTS-FDD or W-CDMA) frequency band or particular4G LTE-FDD frequency band for a different country), when the product is already in the field.
2. Think about the embedded firmware update in the final field installation:
   
   1. If the product will have wireless communications, state how OTA firmware updates shall be completed (i.e., Wi-Fi, Bluetooth, 4G LTE Cellular, Zigbee, LoRa, etc.); this will facilitate creation of the firmware upgrade algorithm.
   2. If wireless connectivity is not present, state that the firmware upgrade mechanism should be done via wired interfaces (USB) or over serial interfaces (RS-232. RS-485), or high-speed interface (Ethernet) .
   3. The firmware update methodology should be easy to use by your service and support partners. In most cases, the end user should not open the product enclosure to perform the Firmware update.

f. Software (Tablet/Mobile Device, local Server, or cloud-based server)


1. State whether configuration software will be needed, how the end user shall be supported.
2. If there is a mobile device or tablet application required, state the OS versions that must be used.
3. Define functional details and screens for all SW applications.

g. User Experience (UX)/ User Interface (UI):


1. It is critical to define the end user experience, and end user interface needs, based on similar products.
2. State your expected end user experience requirements and provide a list of features that will provide great user experience during product operation.

h. Enclosure


1. Do some research for the enclosure/case design, what are the maximum dimensions and mounting method. The size should be able to fit all required PCBA modules, PSUs, interconnecting cables, etc.
2. You can provide initial sketches of the enclosure and discuss ideas with the design team.
3. Determine how the user will interact with the enclosure, if mobile, portable, or handheld, it should be easy to carry and light enough not to require a second person.
4. If possible, create preliminary 3D models and fit suggested components/assemblies inside to see how cooling air (if applicable) will flow, and for ease of manufacturing, and servicing in the field.
5. Note that Enclosure design will be dictated by your stated environmental conditions, thermal management of higher power parts, and regulatory compliance requirements (Safety and EMC/EMI standards).

7. Fabrication


a. Manufacturing (DFM)


1. Your specification should state whether this project will be a Proof of Concept (PoC) or prototype/production devices to be manufactured.
2. If you have information of the various considerations from the manufacturing point of view from your current/preferred Contract Manufacturer, these requirements, stated these as design inputs for the design engineers.

b. Validation testing & Production testing


1. Quality Assurance testing by separate, non-design staff is necessary to find issues and improve the reliability of the product.
2. Request a proper QA validation test plan should be created for both for the validation during prototyping stages, and for PCBA module and/or System production testing. A detailed plan will help HW designers and FW source code developers ensure that the product is easy to test in all stages of NPI development and production.
3. A good plan will state that proper, accessible test points & interfaces, as well as additional firmware code to enable the testing are both required for design validation.
4. For production testing, the time required should be of short duration and efficient. For PCBA module, the product design should have all related test points are accessible; if very high volume or small size, use of automated test setup will reduce setup time and test the product with maximum coverage.

8. Field Use Considerations:


a. Most custom designed circuits will likely fail, so research the scenarios where the product could fail, and how you want repairs (if applicable) will be performed.

b. If you’re a specifying low-cost products, consider if you want the user to ship back the failed product(s).

c. If the product is large or costly, a rugged design is critical. If the product failure is a major type, it will impact the user’s confidence, and your company’s brand reputation. The design should be optimized so that turnaround time should be in minutes (not hours) when field repair is required.

d. You should decide if the product/board is going to be repairable or not, as this fact is useful for engineers during product design; the design team will make decisions that will affect the reliability and repairability of the product.

e. Will your product require service personnel for repairs? This will add cost to the product since you need to maintain service centers with their associated costs (parts, repair documentation, resources, training, etc.).

9. Documentation:


a. Product documentation (Specifications, application notes, datasheets, etc.) are particularly important. This provides information to the end user so they can compare the developed product vs their requirements.

b. Professionally written product documentation with easily readable key features will help the potential client make their decision to buy, while poor product documentation will lead to no or very limited sales.

In addition, the end user needs to know how to use the product safely and effectively.

c. Your product’s user interface should be easy and intuitive to your target market user; the ease of use will define how much support may be needed. Depending on the end user feedback, you may need to create additional documents (FAQs, How To articles, videos, etc.) or even online support group web site to help customers.

d. In many cases, good documentation and support is a critical differentiation for complex use cases, especially when your product uses new technologies.

It is not a simple matter to create a detailed technical specification for most innovative electronic/electrical products. This is usually the case when you don’t have much experience in the design, or you are part of a start-up company with no defined procedures or established guidelines. A well-defined, easily readable technical specification provides clarity to the design engineer and reduces the timelines and wasted time communicating back and forth to clarify important requirements.