How to reverse time

[moddy] sent in a couple of his projects that would probably be entertaining on a Sunday afternoon. The first one is how to reverse the rotation of a battery powered travel clock. It’s just a simple modification of the plate the coil is wrapped around. The second is adding 9V battery terminals to a cell phone. Neither project is practical, but they’re still fun.


  1. Billw says:

    Sometimes the most enjoyable hacks are the ones that have no practical application. You just do them because they’re cool and you can!

    It brings to mind a crazy topic started at the site about how many times a day a clock is right…
    …some of us have too much time on our hands.

    For the record, a backwards clock will be right 4 times a day!

  2. Mac says:

    Hi, I`m looking for any draw program for create clock dial ( reverse )

  3. h says:

    My father has a disabled parking badge which includes a little cardboard dial that you are supposed to set to your arrival time:

    Then the traffic warden looks in your windscreen and gives you a ticket if it’s set to more than three hours ago, or to a time in the future (so you can’t cheat).

    I tried modifying a clock to turn the disc automatically so that it would maintain a constant ~1 hour behind the current time. I didn’t manage to make the clock go backwards and anyway I don’t think it would have had sufficient torque. In the end I used a small stepper motor from a floppy drive, and an 8-pin PIC with an accurate-ish crystal, and had it step every hour. Worked pretty well.

  4. Jim Watters says:

    I took the wall clock my wife put up in the computer room that had a weak battery for over a month so the second had would tick but not move.
    I never looked at it because I have the time right on my desktop. I had it apart, modded, back together, and battery replaced before I even started. Even though it only felt like 10 minutes.

    Waiting for the reaction when she figures out it is moving backwards.


  5. matt says:

    Post #3 (h):
    All you would have to do is put a clock in there, that is half-speed (so 30 mins is 1 hour, therefore fitting 24hrs on a 12hr clock) and set it 1 hour fast. Stick the little time wheel on the hour hand, and TADA!

  6. ben says:

    I must be missing something— how does flipping the insert, which is symmetric, change the direction of the motor? are you swapping the polarity of the winding?

  7. moddy says:

    The plate is magnetic. When you rotate the plate 180 degrees, it changes the polarity from the battery.

  8. Andre says:

    Yeah, that makes sense. The same trick will probably work equally well on a cheap analogue watch, bit more difficult to do though.

    I’ve yet to find a way to get a digital watch to run backwards though, apparently it can be done on some types of mains clock as the chip is an up/down counter.

  9. moddy says:

    I tried it on a watch. It was an $8 dollar analog from Big Lots (one of my favorite places for potential mods) It’s interal mechanism is so small and seam melted together, honestly, you need a microscope and needles to work. I’d like to have one for the novelty though.

  10. h says:

    The little cardboard dial is only 12 hours so you don’t need the clock to run half speed. But you do need it to run backwards – look at the picture I liked and think about the geometry, given that the clock must be mounted behind the card. If it runs clockwise, the indicated time would *decrease*, because unlike a conventional clock you are turning the face with the numbers on it, not turning a hand.

    If I were to do it again I’d try using an ordinary clock movement, modified to run backwards as in the article, driving the disc from the hour hand as you say. But I’m not sure it would have enough torque. Even the stepper motor was prone to sticking occasionally until I loosened the card a bit.

  11. Andre says:

    Yeah, that makes sense. The same trick will probably work equally well on a cheap analogue watch, bit more difficult to do though.

    I’ve yet to find a way to get a digital watch to run backwards though, apparently it can be done on some types of mains clock as the chip is an up/down counter.

  12. Andre says:

    I thought of a use for this hack:- determining the remaining battery life on AA/etc nicads.
    All you do is parallel a resistor and set the time to what it should be (i.e. 2 1/2 hours for a 2500mAh cell) and wait for the clock to stop.


  13. Dustin says:

    Aww, and I was hoping for a time machine hack. =(

  14. The_steven says:

    Ok folks, sing it with me now…

    If I could turn back time…..

  15. vasiliy says:

    This is perfect! You just replace the dial with a its mirror image and you’ve got a clock that runs in reverse yet shows the correct time!

  16. The Steven says:

    Also, “Left-Handed” clocks work the same way…

  17. Jim Watters says:

    Now remember to turn off the bottle cap it is Reverse-Clock Wise. and to put it back on Counter Reverse-Clock Wise?

  18. Gav says:

    I’d just like to say that this hack (the clock) is really nifty.

    In the past I’ve tried (and failed) to do this by reversing the coil wires. I never thought that the non-descript looking peice of metal had a built in polarity.

    So, thanks to the submitter I now have a trendy looking desk clock that works backwards, with a professional looking label. (Surprisingly enough the office photocopier had a ‘mirror’ function).

  19. Jason says:

    I did this with my clock. It wasn’t as easy as the one in the pictures. There were gears on both sides of a plastic plate. The plate needed to be removed to change the direction of clock movement. This made it difficult to put it back in place, but it works backwords now and that’s the key.

  20. Jonathan davis says:

    I’ve managed to do this, really good little hack!

  21. pal says:

    they sell backwards clocks for barbershops, where you can view them through a mirror. i had one given to me and it drove me! this hack allowed me to _fix_ it. so there is a practical application! now to print up a new face in inkscape.

    to mac (message 2) try inkscape. use a circle as a guide, draw it normally then select all and object – flip horizontal. you’ll need x11 installed, if you don’t already have it.

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