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Comment by brc | Hacker News Reader

It's chance.

Even two cars of the same type never seem to match up. They will often sync for a while, but then gradually get out of synch until they are 180 degrees different.

I suppose it is down to minute differences in lighting circuits, bulbs and all sorts of other things.

Somewhere out there is a population of cars with the same exact turn signal frequency as yours. But the chances of you stopping behind it at a set of lights while you are both signalling to turn and noticing are very, very small.

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I believe it's by design. Differing indicator frequencies make the signals more noticeable.

Back in the old days, turn signals were actuated by bimetallic thermal relays - a simple and highly reliable device. They were constructed with a range of frequencies by manufacturers and sold mixed together, so cars might receive the same part number but with an essentially random on/off period. This part would also mechanically create the familiar clicking sound of a turn signal actuating.

These days indicators are controlled electronically and I assume the randomness is programmed in.

That's interesting and kinda funny since you still get the familiar clicking sound when your turn signal is on I can only assume that this sound is made artificially. It immediately reminded me of the fact that computer keyboards are naturally silent but they engineer in "clicky" sounds. This was very important in the old days when people were transitioning away from type writers and were accustomed to the audio feedback. Now we still have this, but keyboards are a lot quieter these days.

There are keyswitches that do click naturally, e.g. buckling spring keyswitches [1]. And it might be subjective, but I type faster with audible feedback, even though it can drive other people in the flat nuts.

[1] http://en.wikipedia.org/wiki/Buckling_spring

They are intentionally made to be different, even on the same kind of car. I think the circuits used to be made with high-tolerance (high-variability) capacitors to make sure they would come out differently. But now it's all computerized, and in fact I think they are programmed to drift a bit faster and a bit slower as they run!

Old hazard lights, like the ones in rows along construction sites, used to blink more-or-less in time despite not being manually synced. The lightbulb itself would act as a weak photo-diode, so when a neighboring light was on, it took a minutely smaller time to charge the circuit. Eventually they would sync up :)

I think the sync is based on firefly physiology. Logo simulation: http://education.mit.edu/starlogo/samples/firefly.htm

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