PCBs
The many paths to electronic prototypes
By Simon Meadmore, global head of IP&E at Farnell T
he range of tools available to assist with the introduction of new products has never been more extensive. Thanks to the improved performance of desktop computer hardware, access to cloud resources and the availability of advanced simulation tools, engineers can model the performance of electronic systems to a high level of detail in the virtual domain as well as the physical domain through prototypes.
In the virtual domain, it is now possible to not just analyse the frequency capabilities and noise levels of mixed-signal circuits, even their electromagnetic compatibility can be assessed before a single integrated circuit is placed on a printed circuit board (PCB). Such simulations can provide a high degree of confidence in design without the need for investment in high-performance test equipment to perform extensive analysis of a circuit design. Simulation can help ensure that mistakes in circuit layout are avoided so the final test can be performed quickly and easily using rented facilities.
Affordable tools, such as those provided by Altium and National Instruments’ LabView, provide not just tools to perform SPICE simulations that are vital for assessing the analogue performance of a basic schematic, but tasks that determine how well a design will perform once placed and assembled. PCB stackup calculators, for instance, can determine the
Simon Meadmore, global head of IP&E at Farnell
parasitics associated with routed traces and signal-integrity analysers will pinpoint potential crosstalk and noise issues.
Hardware prototyping and low volume production
Despite the capabilities of simulation available today, there are many occasions when
36 March 2022
nothing other than a hardware prototype will do. The team may need to use hardware implementations to test assumptions that are too difficult or time-consuming to perform in the virtual environment. For example, there may be a software-programmed control loop designed to run on a microcontroller that needs to be evaluated against real-world signals in real time in order to determine whether it is stable across a range of target scenarios. A software instruction-set simulator may simply not be able to deliver results in a timely fashion or be driven by realistic input data. Another scenario is that the performance of different antennas in a radio frequency (RF) design need to be evaluated and this may be better performed by trying different configurations attached to a hardware prototype. Alternatively, it may be the case that the project has progressed to the point where field trials and early customer acceptance
Components in Electronics
tests are needed. In the context of the Internet of Things (IoT) in particular, it is important to see how multiple devices work on a network with each other and with the cloud. At this point, the team needs to consider the options for prototyping and possibly low-volume production to be able to provide enough hardware to support a satisfactory field trial. A number of options are open to the team. Which is the best will depend on a variety of factors. The choices range from adding custom I/O daughterboards to an existing single-board computer (SBC) to ordering a low-volume production run from an electronics manufacturing services (EMS) partner. If the aim is to ensure that software will perform as expected in a hardware-in-the-loop test of core functions, it will make sense to employ a compatible SBC and have a prototype I/O card made if the off-the-shelf board does not have the required interfaces, or if they do not perform to a sufficient level. Even if the final design calls for a custom PCB design, possibly using a different variant of the onboard microcontroller, the prototype will deliver enough useful information to be justified and minimise any software changes that will be
needed for the production version. By isolating the custom I/O to a daughterboard, the team can minimise the time and cost needed to construct a viable prototype.
Custom-designed prototypes There will be cases when using a combination of off-the-shelf hardware with custom I/O will not perform as well as a custom-designed prototype. Testing assumptions about signal integrity may call for a PCB design that is as close as possible to the final production model. Field trials will often call for hardware that fits into a highly constrained physical or power envelope. The decision then becomes one of the capabilities of an in-house lab to construct a working prototype versus the lead times and cost of having fully assembled hardware provided by an EMS partner. If the complexity of the hardware parts is relatively low, a breadboard-based option may be viable. This can be a suitable choice for the situation where an SBC is combined with a custom I/O daughtercard, as the number of components that need to be assembled onto the breadboard will be relatively low. If the components are mostly discretes, it is
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