Top 10 MCU Selection Mistakes That Cost You in the LONG RUN
A lot of hardware products fail because one early decision pushed everything else in the wrong direction.
In my experience, the one decision that causes the most consequences is choosing the microcontroller.
Once that part is locked in, everything else has to bend around it.
Firmware structure, power behavior, wireless choices, certification, and how hard it is to debug all get shaped by that single decision.
So in this video, I’m going to walk through the ten most common mistakes I see when people choose a microcontroller, counting down from ten to one.
#10 Choosing an MCU with weak tools, documentation, and community support
This usually doesn’t show up right away. Early on, everything looks fine.
The peripherals match, the price works, and the chip seems like a good fit.
Then firmware development gets a few weeks in and progress starts to feel heavier than it should.
The IDE doesn’t always behave, and the documentation explains how things should work but not how they actually behave in real situations.
You go looking for answers and realize there’s not much of a community around the part, no active forums, few real examples, and almost nobody discussing the specific problems you’re running into.
When something breaks, you’re never quite sure whether it’s your code, a silicon quirk, or the toolchain, and there’s nobody out there who has already solved it and written about it.
That uncertainty is what slows everything down.
Schedules rarely slip during schematic design or PCB layout. Those timelines are usually predictable.
Where schedules drift is during debugging, because you’re fixing issues nobody expected, and weak tools, thin documentation, and a small community turn every problem into a long investigation instead of a quick answer.
Teams do ship products in this situation, but every change afterward takes more effort than it should, and that drag never really goes away.
#9 Selecting for features instead of real requirements
This mistake usually starts when the MCU is chosen right at the edge of what the product needs.
The GPIO count matches almost exactly, the memory fits as long as nothing changes, and everything looks efficient on paper.
Then the product evolves a little. You add another button, you realize a status LED would actually help, and those debug pins you didn’t think you’d ever need suddenly matter.
Now you’re deciding whether to bolt on an IO expander chip, juggle signals in awkward ways, or move to a different MCU entirely.
None of those choices feel like improvements. They feel like expensive fixes to a decision that was too tight from the beginning.
Because that experience is both common and painful, a lot of teams swing to the opposite extreme.
They pick a part that can supposedly do everything, with peripherals and features they might use someday. In reality, “someday” usually doesn’t arrive.
Those unused capabilities still increase cost, they influence power behavior in ways you don’t fully control, and they make firmware feel more complicated than it needs to be simply because the device is capable of far more than the product actually uses.
I’ve reviewed many designs where the MCU was doing minimal work and was still one of the most expensive components on the board.
When cost pressure shows up, that decision becomes very difficult to defend.
Good MCU selection sits in the middle. So give yourself realistic room to grow, without drifting into overkill that makes everything heavier than it needs to be.
#8 Overestimating performance needs
More CPU performance feels safer. It gives the impression that the product will never slow down.
But most products are not limited by CPU performance. They spend most of their time waiting on sensors, handling communication, responding to users, or sitting in low-power states.
Choosing a fast MCU for a slow job increases power use, heat, and cost without making the product meaningfully better.
There’s another side effect. When performance feels unlimited, nobody worries about efficiency.
Code gets written in whatever way is easiest, and timing decisions become afterthoughts. Later, when battery life suddenly matters, you find yourself fighting architectural choices that were baked in early on.
Performance should be chosen because the application truly needs it, not because it feels reassuring.
#7 Ignoring real power behavior in the finished product
Power problems almost never come from one obvious mistake. They come from many small decisions that slowly stack together over time.
A peripheral stays enabled longer than expected, or a GPIO configuration leaks a little current, or the firmware wakes the MCU more often than planned, or the wireless stack draws bursts of current that never showed up clearly during early testing.
Low-power modes exist, but using them well depends on decisions made early around clocks, timers, wake sources, and firmware structure.
When those choices are postponed, the product still works, but the battery life comes in far below what everyone expected.
Teams then try to optimize late and discover that the problem isn’t one parameter. It’s the whole approach, and most of the easy fixes are no longer on the table.
#6 Assuming memory is “plenty” without modeling usage
Early firmware almost always fits comfortably into the available memory, which creates a false sense of confidence that space will never become a problem.
Then features get added, logging grows, wireless capabilities expand, security requirements increase, and the free space that once felt generous starts disappearing.
When memory runs out, it rarely fails in an obvious way. You get unstable behavior, features that only work when others are disabled, and builds that behave differently depending on configuration.
Debugging turns confusing because nothing points to a single obvious failure.
By the time this shows up, the choices all hurt. Cut features, rewrite major sections of firmware, or move to a larger MCU and respin the board.
#5 Letting firmware convenience drive the hardware decision
It’s tempting to pick a chip you already know. The tools feel easy, the libraries exist, and early progress moves quickly.
But convenience hides tradeoffs. An MCU that’s pleasant to develop on can still be a poor fit for cost, power, availability, or certification.
Those problems rarely show up in prototypes, and instead they show up later when it’s expensive to change direction.
The result is firmware working around hardware constraints that never should have existed in the first place.
Power budgets get tight, wireless performance becomes unpredictable, and the overall cost structure becomes harder to justify.
Developer comfort matters, but it shouldn’t outweigh the real constraints of the product.
#4 Treating firmware updates as an afterthought
Firmware almost never stays frozen, and products evolve through bug fixes, diagnostics, security updates, and hardware revisions.
If the MCU was chosen without a plan for how updates will actually happen, you run into limits much sooner than expected.
For connected products, over-the-air updates aren’t really optional.
That means you need to plan how Flash will be partitioned, where the update image will live, and how you’ll safely switch between versions.
In most cases, OTA requires enough Flash to hold the current firmware and the new firmware at the same time.
In practice, that usually means needing roughly twice the space you thought you needed.
For wired products, there still needs to be a reliable and maintainable update process that normal operators can use.
If updates require special tools or insider knowledge, they eventually stop happening once devices are deployed.
When update planning is ignored, teams end up freezing features not because they want to, but because there is no safe, structured way to change anything once units are in the field.
#3 Picking the MCU before defining the system architecture
When the microcontroller gets chosen first, the rest of the product is forced to work around it.
Decisions about power, communication, timing, and expansion all start getting made to satisfy the chip instead of the needs of the system.
Little compromises stack up, and the design slowly drifts into something that feels more constrained than it should be.
This is why the system architecture should come first. Map out how the system is supposed to behave, what needs to talk to what, what needs to sleep, and where you may want room to grow.
Once that picture is clear, picking the MCU becomes a supporting decision instead of a limiting one. Reversing that order is one of the easiest ways to create complexity that didn’t need to exist.
#2 Overlooking certification and compliance constraints
This is where assumptions start costing real time and real money. Clocking choices, reference designs, grounding, and wireless implementations all affect EMI and RF performance.
A product can work perfectly on the bench and still fail certification testing.
I’ve seen teams walk into certification assuming it would be routine, only to discover that the fixes required major hardware changes.
The team starts talking about adding shielding, rerouting critical traces, and reworking sections of the board to calm the emissions down.
But unfortunately, in some cases, a full board redesign becomes the only realistic way forward.
#1 Choosing a part without a supply and lifecycle plan
This mistake shows up right when things finally seem to be working. The product performs well, the firmware is solid, certification is complete, and customers are ready to buy.
Then the MCU disappears from distribution or becomes impossible to buy at any reasonable volume, and lead times stretch into next year.
A redesign at this point means a new schematic, a new PCB, porting firmware, and repeating large parts of validation. In many cases, you’re also revisiting certification.
Products stall not because the engineering failed, but because availability was never treated as a design constraint.
If you can’t build consistently, everything else stops mattering.
If you’d like help designing your product and avoiding costly mistakes, then we can help you inside the Hardware Academy.
And if you found this video helpful, then I’d suggest watching this video next where I review four of the best microcontrollers available today.
