Hacker News Reader

Comment by mrtksn | Hacker News Reader

This sounds like a swoftware written by an oldschool electrical engineer or something. I mean, in electromechanical systems that do not have computers, engineers find interesting ways to do more advanced things.

For example, ovens with clocks keep track of time through the grid frequency and if the grid frequency changes, the clocks diverge too.

View on HN

Any time you get cross-disciplinary stuff done by people significantly lacking in experience in one of the disciplines, you get stuff like this. Programmer art (shudder), artist code (double shudder), EE software, software engineer circuit board layout, mechanical engineer wiring... Smart people will figure something out but it always looks janky to specialists in the figured-out field.

Even just between different SE fields this can happen to a degree. Let a C++ programmer write a website with PHP and Javascript - it will probably work, but I'd guess for a web dev the code would look a quite weird.

And the same applies for people criticizing the fields they know little about. I'm pretty sure that not all electrical engineers in the world are idiots and that there's a solid reason why they've chosen the grid frequency as a standard way of doing it. One thing that comes to mind is that the crystal oscillators frequency is very temperature sensitive, so probably not ideal solution for using in ovens?

It's because it saves several dollars on the BOM, and really an oven probably doesn't need a hyper accurate clock

Grid frequency actually is hyper accurate in a lot of places. i.e. in the Western US the grid is regulated such that a clock running off it will never deviate more than 2 seconds from the atomic clock derived National Bureau of Standards time [1].

Compare to a typical quartz oscillator which will gain or lose around 15 seconds per month.

[1] https://www.naesb.org//pdf2/weq_bklet_011505_tec_mc.pdf

This comment should be higher up in the thread.

This is being pedantic but I guess I was saying it's not hyper accurate in terms of time keeping, even though it's pretty accurate in practical terms.

Also, I guess that means my devices with clocks that drift more than two seconds, ie several full minutes, are actually using crystal oscillators? I guess it makes sense for a microwave which needs second level granularity, but that seems odd to me.

Yes.

The crystal in your microwave's CPU clock circuit will drift, and so will the time-of-day derived from it until you set the time again, if there is no external reference. The benefit of using the incoming 50/60Hz AC signal as a timebase is that the power station is responsible for controlling the long term frequency to avoid drift so it can be used as a very reliable reference.

This is the reason.

But often times the "good reason" is that the engineer can quietly solve a problem in their cubicle without fighting an epic political battle that affects multiple departments. From that engineer's perspective, it's a perfectly rational choice.

And that engineer who writes code might be a brilliant engineer and competent coder, but they just haven't been on many software projects before and they don't see how damning that decision could end up being.

It works and everyone is happy, but it's a wart that people have to build around for the next 20 years.

As a software guy I have to point out that often software "engineers" overbuild and abstract the wrong stuff, doing stupid things like making everything a layer. There is way more bad code written by professional software engineers than by EEs, who tend to be more results oriented.

I partly agree, but also, have you seen EE code (from EEs who are not also software devs)? It's not terrible in a "uses php instead of lambdas", it's terrible in a "absolutely zero consistency in variable naming, indentation, or in fact anything, also any comments will consist entirely of broken code or cryptic half-words."

I deal with this stuff semi-regularly in my day job and wow.

I could live with all that crap, but what kills me is the unnecessary global state. Everywhere, particularly when it's not needed.

It's a complete nightmare to integrate with the rest of the application.

Oh, yeah I forgot to mention the “global-first” memory management style. So scary.

It's because of cost and because grid power is generally very accurate (at least in the US). No one cares if their oven clock loses 10 seconds per year, and "white goods" (appliances) are generally designed to minimize costs as much as possible. The electronics in a typical oven are very simple, and using the power line as a frequency reference is very easy and cheap to do.

Also, crystal oscillators aren't that accurate. You can make them more accurate by heating them to a given temperature, but this is something only done in expensive test & measurement equipment.

There was a really interesting anomaly last year where, due to a political dispute, Serbia and Kosovo refused to synchronize their grids, causing the entire European grid to drop from 50 Hz to 49.996 Hz, in turn causing grid-based clocks to run 6 minutes slow by the time the issue was resolved. [1]

I don't disagree with you that grid frequencies are generally very accurate and they are a practical clock source for cheap clocks, I just found that interesting.

[1] https://www.reuters.com/article/serbia-kosovo-energy/serbia-...

Also they know the incredible effort that goes into keeping the grid synchronized and that if any generator is out by any significant fraction of a waveform then a few fast oven clocks are the least of their problems.

and famously if there's ever a blackout, most of modern ovens will refuse to work until you setup the clock... never seizes to piss me off each time I have to do it...

This is a security feature. Most modern ovens allow you to set a timer with auto shut-off. This is very useful if you want to go out and come back to a ready meal. You can imagine what would happen if the power went out for a while and after it came back the oven switched on automatically. Refusing to turn on the oven when the clock is not set is the easiest way to prevent problems when it is in use.

good point... still, quite annoying when you come to check your meal cooking in the oven for the last hour, only to find out that it never actually switched on because of the clock :)

Reply on news.ycombinator.com