The faulty digital clock problem (2021)

for years I was faced with a similar problem, but my constraits were different so I was able to definitively solve it a different way.

Sony made a bedside alarm clock-radio back in the 80's—actually two models, a mono- and a stereophonic—that had a rare feature that I loved: you set the alarm with two dedicated and detented knobs, one to set the hour, and one to set the 5-minute mark for the alarm, and the alarm could be the radio. I would have the alarm go off every morning to either a classical or npr (back when it was listenable :) station. I loved that I could set the alarm just by reaching out in the dark and turning the knobs, as I could tell by feel what they were set to. I felt sure this idea was going to take over alarm clocks worldwide! Instead, even Sony dropped it a couple years later.

for at least 15 years I kept this alarm clock with me as I moved cities a couple times. Unfortunately, the nixie tubes for the time display went bad so it became hard then impossible to read the numbers. I struggled with that for awhile, then I realized, I didn't care to read what time it displayed, I just needed the alarm to work. So, I would unplug it (and the 9V battery backup) and plug it all back in at midnight; A broken clock being right twice a day, that's the time it would assume. Got to use my favorite stereo radio for a number of additional years. It even lasted into my subsequent and on-going "I will never buy anything from Sony, ever again" boycott :)

edit: found a picture of it https://images.bonanzastatic.com/afu/images/8ddb/9523/9356_8...

guess it wasn't nixie, some type of gas flourescent though. also, 24 hr clock so I guess it was right once a day.

This was a really neat read! It's fun to speedrun the experience of "I've never thought about this" => "There's a structure to map out here" => "I wonder how this is solved in general?" => the nitty gritties of hashing out a solution. Thanks for sharing!

I once pondered about a much stronger version of this problem, where not only you don't know which segments are faulty, but also you can't tell one state from the next state that is identical to the previous (i.e. no forward button, nor known update interval), and you don't know which variant glyphs for some digits are used. I was partly motivated by digital clocks in a bus, which I could never continuously observe, explains those changes. Obviously they had a great impact on the number of possible states---somewhere around ~100K states---and my attempt to draw a reasonable graph out of them was futile.

Discussed at the, er, time:

The faulty digital clock problem - https://news.ycombinator.com/item?id=27346655 - May 2021 (16 comments)

Nerd sniping indeed! Upvoted

I find it interesting that in 2024 there is a significant portion of the population that would probably die in the escape room. No matter how long they were given to consider the puzzle.