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        riddles >> medium >> The broken clock
        
(Message started by: Frost on Jul 26^th, 2002, 2:44pm)

Title: The broken clock
Post by Frost on Jul 26^th, 2002, 2:44pm

My fancy new digital alarm clock is broken! :'(

The time 'jumps' around.
When I reset it, it reads 12:00:00. Then it runs as it should, but after 12:04:15 it resets back to 12:00:00. It counts up to 12:04:15 again and then it jumps to ... 12:08:32 ! Weird stuff.

Do you know what's wrong with my alarm clock?

Title: Re: New Riddle: The broken clock
Post by william wu on Jul 26^th, 2002, 4:30pm

heh, at first i thought your clock really was broken and that this was some kind of lame joke. ;)

fascinating. i'll definitely think about it. thanks!

Title: Re: New Riddle: The broken clock
Post by Mark Davis on Jul 26^th, 2002, 8:00pm

Hmm, 4:15 = 255 seconds. 8:32 = 512 seconds. Sounds like there's a binary counter in there somewhere..

Title: Re: New Riddle: The broken clock
Post by Mark Davis on Jul 26^th, 2002, 8:03pm

Maybe a binary clock readout with the 8'th light (2^8 = 256) burned out.

Title: Re: New Riddle: The broken clock
Post by william wu on Jul 27^th, 2002, 12:07am

I have added this cool new riddle to the archive, and I would really like to credit you, but I don't know what your real name is! Currently you are just credited as [Frost]. If you're interested, you can send me your real name via e-mail: wwu@ocf.berkeley.edu.

Title: Re: New Riddle: The broken clock
Post by Frost on Jul 27^th, 2002, 7:50am

Yay! I scored a medium on the Wu-scale! ;D
You can credit me under my irl name, which I mailed you.
Mark: http://www.tuxedo.org/~esr/jargon/html/entry/off-by-one-error.html

Frosty.

Title: Re: New Riddle: The broken clock
Post by john on Aug 19^th, 2002, 4:13pm

don't know if this is the "why" but your clock seems to be counting each second alright. it would be helpful to hear what is happening after it reads 12:08:32. because, at 12:08:32 it is back on time again. count out the seconds. don't forget to count the two seconds it takes to change the readings from the first 12:04:15 to 12:00:00 and from the second 12:04:15 to 12:08:32. somehow i don't think this is the answer to the riddle though. thoughts anyone?

Title: Re: New Riddle: The broken clock
Post by Icarus on Oct 17^th, 2002, 6:22pm

Here is my answer:

The clock uses a counter to track seconds since midnight. The value of the counter is sent to a separate circuit which converts it to a standard time display. Since the clock displays seconds #256-511 the same as seconds 0-255, the 9th bit of the counter is not reaching the display circuit. The counter itself must be okay, since it resumes a correct display at second #512. Apparently, there is a short in the wire for bit 9 of the data bus from the counter to the display circuit.