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Comment by PascLeRasc | Hacker News Reader

I had one of these for an interview a few months ago. A huge schematic and I was told to find out "why it wouldn't work". It took me about 10 minutes to figure out that one FET's diode network was set up so that it'd short out and fail, and I ended up failing the interview for taking so long and labeling every subsection. They told me this was a spot test, and this kind of thing should just jump out immediately if you're smart enough. They also said me immediately jumping into the details of each component and its role was a red flag and they didn't think I'd be able to get the big picture of circuit design.

I've been thinking about this since and I don't know how I can fix this. I just don't know any other way to think other than looking at the details. Does their assessment that this is a flaw seem on point?

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Sounds like the interviewer tried to use this tactic, and did a lousy job of applying it.

1) "Why it wouldn't work" is vague and nonspecific. "Applying power and hearing a pop/smelling smoke" is a big hint. You have to phrase the question in a way that gives up some information for it to be a decent use of time.

2) Complexity fucking kills these interviews. You shouldn't be handing off a multi-page schematic with complex interconnects. Five or six major components, max. Label your subsections for clarity: things like "microcontroller", "EEPROM", "LED driver", "half bridge driver", "ADC", etc.

Sounds like you did the right thing, and got penalized for it. Fuck 'em. They weren't the right fit for you anyway.

Ok, to be fair, they did say "when we turned it on, part of it blew up" when I asked for more details, and it was just a 2-page schematic with 6-7 subsections. I think it was pretty fair, I'm just frustrated that it felt like I couldn't solve it by thinking slowly and methodically.

It was a really cool company and I'd have loved to work there. It's the kind of place where I want to be a good fit.

I do wonder if this is just a scenario where there's no way to win. The person writing this blog post has exactly the same interview prompt - something went pop when the board was powered up - but they expect candidates to spot subtle things like missing decoupling capacitors that almost certainly aren't the cause of the problem.

Just about every person I've used this prompt on has found the prompted error, and then gone on to find a few more. However, I don't really care about the number of errors you find nearly so much as I do seeing and hearing you reason your way through a new problem.

I don't expect you to find all the issues. (But if you do, then congratulations! I'm gonna try to hire you.) I do expect you to talk to me about your thought process when confronted with a novel issue.

That's what good electrical engineers do. They don't know all the answers - they reason their way through unexpected challenges.

Did they tell you exactly where it blew up? Then it might be fair, 2 pages is not that big. Though you'd still be at quite a disadvantage compared to someone who spent a lot of time designing the thing.

I gotta say though, if they themselves designed this board that promptly blew up, perhaps they should recalibrate their expectations for EEs.

I started doing board level design and firmware in 1984. What's that now, 35 years? I'd rather have a methodical EE than smug cowboys like those guys.

They failed you for doing what any competent engineer would do.

Hard to say for sure, since I don't know you or the company and can't see the test myself. It is a legitimate skill, especially in higher-level engineering positions, to take a huge pile of code or schematics or whatever and get a high-level understanding of what it seems to be doing without getting too bogged down in over-analyzing any particular sub-section too soon. Some things do tend to jump out easily when you have a sufficient level of experience with the overall domain.

I would suggest it’s not about “being smart enough”, but about pattern-matching. Over time, the brain gets trained to recognise things and react without conscious effort. You haven’t put in enough repetitions to get to that point yet, for that interview.

I think you lucked out actually. Interviews go both ways.

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