My goal is to take a typical white clock and make it light up green at 3pm, yellow and 6pm and red at 9pm

I'm guessing I'm going to need 6 red led lights, 6 yellow led lights and 6 green led lights

What I'm not sure about is how something on a timer switch would be wired up, would I use transistors, diodes or something else

The clock is run off of 2 AA batteries

  • \$\begingroup\$ Complexity is added in sensing the big and little hands at those positions to advance the light sequencer which might be more than you expect , then the LEDs will consume more power than the clock itself normally draws reducing the life of the batteries significantly. So it becomes a problem. \$\endgroup\$ Commented Dec 19, 2018 at 1:24
  • \$\begingroup\$ I can add more AA batteries, just tell me how it's done and I'll figure what I'm missing \$\endgroup\$
    – user184118
    Commented Dec 19, 2018 at 1:29
  • \$\begingroup\$ you would be missing about 2 batteries per day. \$\endgroup\$ Commented Dec 19, 2018 at 1:40
  • \$\begingroup\$ @TonyEErocketscientist do they still make clocks with big and little hands? If so, does anyone under 40 know how to read them? Is it 3:15 or quarter after 3? I'm pretty sure the clocks with big and little hands only need one AA battery. Dem dare new fangled clocks are the ones dat need two AA batteries. \$\endgroup\$ Commented Dec 19, 2018 at 2:27
  • 1
    \$\begingroup\$ OLd is relative. THIS is an OLD alarm clock: ancientpages.com/2016/05/06/… \$\endgroup\$ Commented Dec 19, 2018 at 3:31

1 Answer 1


would I use transistors, diodes or something else

Seeing LEDs are diodes, we'll go with a yes to diodes.
Transistors? Very likely if you want to use the clock's LED driver.
You would configure the transistors as logic gates.
The "something else" could be resistors.

enter image description here

Your clock would need to be a digital clock with 7 segment digits.
You would need to know the pinout for the 7 segment LED driver.
You would need to know the driver's current and voltage for each segment.

You would drive the logic gates with with two of the clock's segments.
Build a logic table for the segments when the hour digit is a three, six, or nine. You need a logic combination that will have a unique output for each of these three digits. The outputs of the logic gates would drive another transistor that turns the LEDs off and on. OH! Look, more diodes!

enter image description here

It's not going to be easy to use the drivers in the clock.

Your best bet would be to use a microcontroller with a realtime clock to drive the red, yellow, and green LEDs. It will work with any type of clock, analog or digital.


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