Should designers use off-the-shelf parts?
05-11-2020 | By Robin Mitchell
Developing a solution often requires multiple stages of prototypes before a finalised design can be made. However, designers should be careful when using off-the-shelf parts as while these may present opportunities, they can also be highly problematic.
What are off-the-shelf parts?
The term off-the-shelf refers to parts, components, or modules that themselves serve no specific purpose, and thus can be integrated into many different applications. Some off-the-shelf parts will have characteristics aimed at key areas (such as aerospace and military). However, even then, the functional capability of these parts still allows them to be used in many different applications. However, while components such as resistors and capacitors could be seen as being off-the-self, the fact that all electronic circuits are built using such parts makes it harder to define them as being off-the-self, and instead be defined as a fundamental component. The same holds for many ICs including CPUs, microcontrollers, and controllers as these are needed for most circuits to function. But, if such a circuit needed to be serviced in the field and found to require an IC replacement, then the term off-the-shelf could apply as the IC that has failed may be available from different manufacturers (thus, an off-the-shelf part).
So, what does off-the-shelf imply in the electronics world? Generally speaking, off-the-shelf parts are those that refer to modules and systems that contain all the circuitry needed to perform their operation, and such parts can often be connected without the need for adding more circuity. Such off-the-shelf parts include Raspberry Pi’s, beagle boards, Arduino development boards, and sensor modules. Many of these parts are found in the maker world, whereby projects can quickly be prototyped and constructed with little hardware effort. Still, others can be found, such as Wi-Fi modules that integrate a microcontroller, RF front end, and shields to produce a near-complete product.
What advantages do off-the-shelf parts present?
One of the biggest advantages of using off-the-shelf parts in a project is the speed at which a project can be prototyped. Instead of needing to design the circuitry at the component level, a project can be put together in a matter of hours, often using temporary wire connections between different subsystems. From there, the designer can focus on tasks such as software development which allows for the project to be developed in a much shorter time. Another advantage to using off-the-shelf parts is the price; while designing circuits from scratch can be cheaper in bulk, purchasing premade modules is far cheaper when only creating one or two prototypes. This brings us into the third advantage which is development costs; the ability to quickly develop a design while using off-the-shelf parts significantly reduces project costs as engineering time is reduced and major problems with a design can be determined early on.
Once out of the R&D stage, products that are deployed in their final application can then continue to benefit from off-the-shelf parts. For example, if parts of the design fail, they can be easily replaced as those components are already widely available. Designs that utilise off-the-shelf parts are also more likely to use a construction method that is easy to take apart and put back together, thus making it easier for trained technicians to both service and repair the end product. Furthermore, if parts can be replaced, then those systems hardware can more easily be upgraded as technology progresses. For example, a system that utilises the Raspberry Pi 2 as is processing core can be upgraded with the use of the Raspberry 4, and software updates allow for more functionality.
What disadvantages do off-the-shelf parts present?
Using off-the-shelf parts during R&D of a product or solution carries very few disadvantages as this stage is designed for experimentation. Thus a solution that can be quickly put together and tested is ideal. However, not all applications can benefit from off-the-shelf parts during development (such as a high-speed bus link between an SoC and a memory IC). Thus the use of off-the-shelf parts may not help with the development of hardware. If a project does require the use of custom hardware, then off-the-shelf parts can increase the overall price of the development stage, but this point becomes mute if the use of custom designs only requires many iterations before getting the design correct (i.e. off-the-shelf parts can help to prove a design before committing to it).
However, the project will eventually need to leave the R&D stage and move into the deployment stage. From there, designs that use off-the-shelf parts can quickly run into issues including cost, reliability, and security. Cost is a major issue with off-the-shelf parts; while it may be cheaper to produce one or two designs with off-the-shelf parts, manufacturing thousands can become enormously expensive. A design that uses a custom PCB and carefully chosen components will always be cheaper when producing in bulk. This is why most, if not all products, on the market utilise custom PCBs using the bare minimum number of components needed to make the product function.
Depending on how the end product is physically constructed, using multiple modules connected using wires will never be as reliable as a single or multiple PCBs with specifically designed connectors. Sources of mechanical vibration, wear and tear, and other unexpected external forces can result in wires becoming loose and modules failing. While custom made PCBs can also suffer from the same issues, they are far less common due to the use of permanent wire fixtures and joining techniques.
Security is also another major issue to keep in mind when designing a product using off-the-shelf parts. The use of commonly available parts, such as single board computers, opens up a design to potentially well-known bugs and flaws that attackers could exploit. From there, not only is a device vulnerable from attack but so is the inbuilt intellectual property found in code and software that runs the system. The use of off-the-shelf parts also opens up a design to attack with the use of generic operating systems that may leave ports open, store unnecessary information, or have inbuilt remote access (such as SSH), that can provide alternative entry points for an attacker to exploit.
Should you use off-the-shelf parts in a design?
Overall, the use of off-the-shelf parts in a finalised designed should be discouraged for reasons of safety alone, but this again depends on the end application as well as the intended number of installations. For example, a one-off solution in a factory can greatly benefit from the cost savings of using off-the-shelf parts while also taking advantage of easy repairability. However, a product that will be found in millions of homes should not use off-the-shelf parts for both cost and security reasons. Thus, when deciding to use off-the-shelf parts, a designer must consider all aspects of their end application but generally speaking, it is best to avoid off-the-shelf parts for any commercial solution.
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