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quote:
Originally posted by pennsyfan:

A friend wants to build one; and he is finding that all the clocks he would use to modify are of a single chip type which makes it almost impossible.


What's his budget?

By "build one" is he really trying to hack a $10 consumer digital clock?

Is the issue he can't find a datasheet for the chip? Or has he already used a scope to poke around the various signals and the issue is, say, how to convert a 60 Hz reference signal to a 240 Hz signal to make the clock run 4x faster?

What about the boat-load of digital clock kits out there that come with schematics? Some use a dozen or so chips to do the counting and 7-segment display control (rather than a single chip clock IC) and hence you'd have arguably better access to inject a 4x, 8x, or whatever signal to make it run faster. If he goes the kit approach some use Nixie tube displays for an eye-catching retro look.
BTW, we are talking digital clock? I'm assuming given his dismay at finding a single-chip circuit.

That is, the analog wall-clocks I've seen use a gear mechanism to cascade the second-hand movement to the minute and hour hands. So all you provide is a 1 pulse-per-second signal (derived from a 32.768 kHz crystal for battery-power, or from 60 Hz if line-powered) to drive the second-hand movement and you're done. I don't think you'd ever need more than 1 chip to do so.
All,
Thanks so much for jumping in here. I had never used a fast clock, so I turned to the forum for help. The text below is from an email that I received today. It looks like the originator (Jim) found something to his liking. There was definitely good source information exchanged here in these forum posts.

Hey Bob, (Me)
Thanks for you assistance and effort. I got this from my friend yesterday. Looks like he figured his solution. I forwarded him the websites you sent anyway because he'll probably find them interesting. Thanks again.
Bob (my friend)

Hi Bob, (my friend)
I think I found a solution. I did some more reading (for Christmas I got a DVD set of every issue of Model Railroader magazine ever, from 1935 through 2009), and I found a more current article. I looks like it is relatively easy to take a battery operated quartz movement, and remove the crystal oscillator, and then replace it with a 555 timer arranged to send out signals at the desired rate. Ironically, I already have a bunch of the almost exact circuit in use as blinkers for LED's in crossing signals, warning lights, etc. I just need to change the resistors and capacitors to raise the rate. If it works, I'll let you know...you can pass it along to your model railroading friend.
On an amusing separate note, it's funny reading the really old issues of the magazine and seeing the different mindset back then. One phrase from an issue in the 40's was great. It said "just use whatever wire you have left over from the last armature you rewound"
Jim
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