Your prototype works. You plug it in, it does exactly what it's supposed to, and your brain tells you you're almost done.

That little voice in your head is lying to you, and it's about to cost you months of wasted time and a pile of money.

Because a working prototype hides a whole stack of problems that don't show up until you try to turn it into a real product you can actually sell.

So I'm going to show you five things your working prototype is hiding from you, and why each one can blindside you right when you think you've crossed the finish line.

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Lie #1: "I just need to put my parts on a PCB"

This one fools almost everyone, because your prototype already works, so it feels like all that's left is taking those same parts and laying them out on your own board.

When you build a prototype, you're usually snapping together modules, dev boards, and little breakout boards.

Those boards exist to make your life easy, and that convenience is hiding a ton of work from you.

A part that shows up as a nice tidy breakout board today might be a tiny fine-pitch chip on your own board, with pins so small and close together you can barely solder them by hand.

Or it could be a chip with no leads at all that has to be soldered flat against your board, which is a whole different level of difficulty to design and assemble.

A wireless module is even sneakier, because it hides the antenna, the radio tuning, the shielding, and the certification work, all in one tiny part.

You get to keep all of that as long as you use the whole module, so the real trap is putting the raw wireless chips on your own board just to save a few cents.

And if any of your parts run fast signals, like USB or a camera or external memory, your board has to be laid out very carefully, because those fast signals are picky about how they're routed.

The moment you put those same parts on your own circuit board, you've started a whole new project.

If any of that layout work is off, getting a corrected board made and assembled is another several weeks and a few thousand dollars, before you even find out whether the fix worked.

And your prototype told you nothing about how big that project actually is.

Lie #2: "It's reliable, it ran on my desk for a week"

Getting one unit to run on your bench is the easy version of the problem.

But keeping thousands of units working across heat, cold, vibration, humidity, and years of people dropping them is much, much harder.

One unit sitting in a nice controlled room on your desk tells you almost nothing about how a full production run behaves once it's out in the hands of real customers.

Every component you use has tolerances, which means no two units are ever exactly identical, and the weird failures only start showing up once you've built a lot of them.

Back when I was at Texas Instruments, a sharp new engineer joined the team and started designing his very first chip.

He got the first batch of chips back from the factory, tested one, couldn't find a single problem, and came to me bragging that he'd hit first-pass success, which almost never happens.

But a few days later they tested more units, and the whole thing fell apart.

The design had a fundamental flaw that made the chips vary way too much from one unit to the next.

It was baked so deep into the design that there was no fixing it, so he had to scrap the whole thing and start over.

And it doesn't matter whether you're designing a chip or a whole product, one good unit on your bench just isn't proof that the rest will hold up.

That's the trap, and the way you get ahead of it is to test hard across temperature, vibration, humidity, and plenty of units, before your customers find the problems for you.

Lie #3: "The firmware is basically done"

Bench firmware and the firmware that actually ships in a product are two very different things.

When you're the only person using your prototype, your code only has to work when everything goes right.

A real product has to keep working when things go wrong, and out in the world a lot of things will go wrong.

You've got to figure out how the factory is going to load your firmware onto thousands of boards quickly and reliably, which usually means building a custom jig just to program every board on the line.

Then there's the watchdog, which is a little timer that automatically resets your chip if the firmware ever freezes, so your product doesn't just sit there dead in a customer's hands.

And you need to handle the ugly edge cases that never come up when you're the only user, like the wireless connection dropping right in the middle of sending data and corrupting it.

Worse, a firmware bug you find after production means reloading the software on every single unit, or even pulling them back from customers.

So the firmware that feels basically done on your desk is usually nowhere near ready to ship.

Lie #4: "Power is handled, it runs fine"

Your prototype has been plugged into USB through a dev board this whole time, so your power consumption never even came up.

Nobody measured how much current it draws while it's sleeping, and nobody bothered to look at your duty cycle, which is just how much of the time your product is actually awake and working versus sitting idle.

That dev board is also covered in extra parts like voltage regulators, status LEDs, and USB chips that all burn power and won't even be in your final design.

Your bench setup is hiding your actual battery life from you completely.

This is how people end up designing a coin cell product that's supposed to run for a year, and then the real thing dies in about a week, because the background draw was way higher than anyone measured.

For most battery products, it's the sleep current that decides your battery life, not the active current, because the device spends almost all of its life asleep.

Even when a coin cell still has plenty of charge, it can't push out a big, sudden burst of current due to its high internal resistance, so the moment your radio switches on, the voltage can dip far enough to reset the whole chip.

And the worst part is you usually find this out after the design is already locked in, when fixing it means starting a big chunk of the design over.

So if you care about battery life, measure your current draw early, because "power is handled" really just means it's handled on USB.

Lie #5: "The enclosure works, I 3D printed it"

A 3D-printed enclosure can fit together perfectly in your hand and still be completely impossible to mass produce.

3D printing will build almost anything you draw, with no rules about how the part is shaped, which is great for making prototypes but does nothing to get you ready for real manufacturing.

Once you move to injection molding, which is how plastic parts get made in volume, a long list of rules suddenly applies.

You need draft angles, which means the walls have to be slightly slanted so the part can pop out of the metal mold instead of getting stuck inside it.

You also have to keep the wall thickness consistent, because thick chunks of plastic shrink and warp as they cool and leave ugly dents in the surface.

And you can't have undercuts, which are little lips or hooks that physically trap the part inside the mold, unless you pay a lot more for a mold with moving parts, called side actions, that slide out of the way to free it.

On top of all that, every separate plastic piece needs its own steel mold, and those molds run thousands of dollars each and take weeks to cut.

I taught myself injection molding for my own product, and the gap between what prints just fine and what actually molds was a lot bigger than I expected.

So your prototype enclosure can feel completely finished, when really it's hiding the part of the project that catches most people off guard.

All five of these lies point at the same thing.

A working prototype tells you almost nothing about whether you can actually build your product at volume.

That jump from one working unit to thousands coming off a production line is the actual project, and how hard it is depends entirely on the details of what you built.

Some of those jumps are pretty easy, and others turn into a months-long nightmare, and most people have no idea which kind they're sitting on.

And don't count on the factory to save you, because your manufacturer just builds whatever design you hand them, they don't fix it for you.

Every one of these problems stays your problem until somebody who knows what to look for actually reviews your design.

Cheers,

John Teel
Founder / Engineer
Predictable Designs