Greater Clarks Hill Regional Library


Seconds: How Do They Work?

Sam Link
Oct 19, 2015

The title. I’m not kidding. Calculating the passage of time baffles me.

If you go to the ground floor of the Columbia County library, in the Young Adult Room, you’ll find a big sign that says “READ” with flashing lights around it. I program the light display, and at least 80% of that time is spent calculating how many seconds it takes each part of the display to finish.

And I’m never, ever right.

I miss a loop, and it might just be a tiny loop that cycles five times, but that’s a multiplicative mistake – if the part inside that loop is timed out at two minutes, then we just went from a two-minute display to a ten-minute display. And then that’s in another loop, and suddenly we’re up to over an hour of the same pattern.

I discovered this, not by sitting and watching the display – after all, I did the math on it, I know everything runs for two minutes, two-and-a-half tops – but by setting up a camera so I could show the display to other counties. 45 minutes, and exactly one pattern runs.

So I run the math again and discover I’d left out a loop that runs eleven times in my calculations, which makes the inner loops run more than I estimated. Then the inner loops were calculated at two minutes each, not at 1/22nd of two minutes. Moreover, the delay was per bulb, not per loop. What was supposed to be two minutes had become one-thousand, eighty-three minutes and forty seconds. Put in perspective, there are only one-thousand, four-hundred forty minutes in a given day. So, at any given point, a patron was probably seeing slowly blinking lights.

My wife is in precalculus right now, and every once in a while she asks me “Who actually uses this?”

I tell her about the light show. She clarifies with “When am I or any normal, sane person going to use this?”

And, honestly, I have no idea. But math is important, and when you’re figuring out how many times a light show can loop to add up to 120,000-150,000 milliseconds in units of 20-50 milliseconds per flash of a bulb math becomes really important.

Anyway, you should really go look at the light show down there – the Halloween part looks awesome, and it’s the kind of thing you learn to do in the Makerspace. It’s all run off an Arduino – a tiny, basic computer capable of simple commands and automation – and learning to program one is a Makerspace activity, in addition to soldering the lights together, connecting the power supply, etc. Plus, you’ll have a chance to learn about 3D design, sewing, weaving, using a basic recording studio, video editing, and more.

For more information, you shouldn’t contact me; talk to the young adult librarian downstairs. Or send me an email and I’ll get it to him.

Sam Link
System Services Librarian