Kenneth MacCallum

I Hate Wires

Does this conversation sound familiar?

KM: How’s the product design going?

EE: The PCB designs are done.

KM: How do the boards connect to the motor, heater, laser, each other, etc.?

EE: I put connectors on the board. We’ll wire them up.

KM: When will you do that?

EE: When the boards arrive.

I have learned not to be too subtle while having this conversation because others often don’t get that shiver of fear rattling down the back of their necks like I do. There are very few things more frustrating than spending a day or more in the lab wiring up a new system when missing your deadline is already imminent for other reasons.

Fortunately, I’ve found a very pleasant solution which I now brutally evangelize: avoid wires. I ‘m not pushing RF or IR: I mean wireless in the “less wires” sense. Even before a product is a twinkle in anyone’s eye I’m lobbying to remove wires. I know that’s maybe a bit unreasonable but if you don’t have lofty goals then you’re doomed to mediocrity.

So how do we do it? We use those very PCBs that required the wires in the first place. Instead of choosing connectors which must mate with wires, we choose board-to-board ones. Instead of making boring, rectangular PCBs, we make cool, odd-shaped ones that fit intimately with the other hardware bits. Connectors to the outside world are put on the same plain; controls, switches and indicators are chosen and located so they are board-mounted. Finally, we do all of this in a way that doesn’t make the Industrial Designers hate us.

I can picture the unbelievers in the room shaking their heads: “How can all of that be ‘simpler’ than just wiring things together with a good, old-fashioned wiring harnesses?” Well, the simple answer is that it’s not, but often only by a tiny little bit. Even wiring harnesses must be designed, wire lengths specified, connector housings and crimps chosen, BOMs built and procedures written. Of course this assumes that we’re going to document the wiring properly. We are, aren’t we?

If the effort is a wash, what’s the real advantage? Timeline. Back in the early stages of the detailed design of the product, the interconnection strategy can be worked out through collaboration between the electrical and mechanical engineers. The boards and mechanical parts are designed pretty early in the process and so the interconnection is too. This is in contrast to the week before the first prototype ships if you defer it all to a complex wiring harness.

Let’s not fool ourselves though, there will always be wires. How do we prevent even the small amount left from causing grief at the last moment? We design it as best we can up front. Wire lengths and routing can be estimated early during design; components can be chosen back then too. It all can then be built early, even subcontracted. When the boards are in and the initial power-up and debugging took longer than expected, you can at least take comfort in knowing that you won’t waste that day or two mucking around with crimpers and things when you should be tackling the deeper problems that you haven’t even discovered yet.

Let’s not leave it down to the wire.


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