How would I rig an old analog clock to light up LEDs to show the time?

 I was thinking of using the 10mm ultra-brights for the hour mark and the standard 5mm for the minutes. Should I connect them all to a common ground and use the hands as the "hots?" Should I use a plate-type contact; cause I feel that the post-type would interfere with the sweep of the hands. What kind of batteries should I use?


orksecurity6 years ago
Difficult. You'd have to somehow make the hands trigger switches without putting so much drag on them that they slip (remember, they're just a press fit onto the shaft) or stop the motor (remember, it wasn't designed to do more than move the hands!).

I'd suggest using optical interruption to pick up the hands' passing. Except that by the time you've gotten that complicated, you might as well just get a clock chip and have done with it.
I am guessing that you want 60 LEDs total, twelve10mm ones marking the top of each hour, and forty-eight of the 5mm kind in the other spots, arranged in a circle around the periphery of the clock, evenly spaced every 6 degrees, or 1/60th of a circle.  Moreover I am imagining only one LED is illuminated at any instant in time, and each LED is illuminated for 12 minutes, or 1/60th of a 12 hour period. 

That is to say the hour hand is always approximately pointing at the illuminated LED. The big 10mm LEDs, (Maybe they're a different color too. That'd be fun.) are illuminated at the top of every hour.  That is: from [h:00m:00s] to [h:11m:59s]

LED:  10 mm, 5mm, 5mm, 5mm, 5mm
time: 12:00, :12, :24, :36, :48
      1:00, :12, :24, :36, :48
      2:00, :12, :24, :36, :48
      3:00, :12, :24, :36, :48
      4:00, :12, :24, :36, :48
      5:00, :12, :24, :36, :48
      6:00, :12, :24, :36, :48
      7:00, :12, :24, :36, :48
      8:00, :12, :24, :36, :48
      9:00, :12, :24, :36, :48
     10:00, :12, :24, :36, :48
     11:00, :12, :24, :36, :48


If it is an "old" analog clock utilizing either quartz timing, or sync'd to the power timing, then you can just use a whole bunch of digital counters with decoded outputs (like the CD4017), or a microcontroller capable of driving 60 LEDs somehow, as long as you find a way to sync the 0-to-59 counter you build, with the same signal, the same train of pulses, that is driving the clock's hands.

In other words, build a simple digital clock and install it into the same case as the analog clock. That might indeed be the simplest answer.
Exactly! With the provision that the two clocks be locked to the same source of clock pulses, so that they march in step, and stay synchronized.

Although modern quartz timing is pretty good, so even if you had two independent quartz-timed clocks, in the same case together, it might take a while (days? months?)  for the two clocks to drift noticeably out of agreement with each other.  So I guess that would kinda work too.