Clock Face

Our house came with this clock in the kitchen. The clock runs several hours fast per day, making it completely useless for telling time. So of course, I took it apart and messed with it.

I was hoping to find some timing adjustment inside, but the clock must have cost around 5¢ to make, leaving no room for such niceties. In the end I just figured out the gear assemblage and put it back together.

Here’s the insides:

Mechanism Front
Motor Diagram

The motor on the left is rather clever. There’s an IC on the back containing the piezo. Every second, this reverses the polarity of the attached coil, causing a magnet to flip over. This makes the ‘click’ sound in electric clocks. Unfortunately, I can’t do anything to fix a faulty IC circuit.

Mechanism TopGears Diagram

Gear layout. The motor drives gear 1 (omitted from photograph), which is transmitted to the second hand (3), the minute hand (5), and the hour hand (7). Gears are labeled with the number of teeth.
Gear Ratio to previous time/revolution
1 2 sec
2 4 8 sec
3 15/2 60 sec
4 15/2 15/2 min
5 8 60 min
6 3 3 hr
7 4 12 hr

One thing I was unable to figure out is the mechanism keeping the magnet flipping in a consistent direction. So as a prank/experiment I reversed the leads on the motor coil. We’ll see how long it takes my roommates to figure out that the broken clock now runs backwards.


3 thoughts on “Hardware Hacking: Clock

  1. So did they ever notice that time was running backwards? Of course even under conditions of inverted chronality a clock is right twice a day!

    1. They did eventually notice, after a couple days.

      I think one of the gears is getting worn out so that the second hand tends to slip. So it might not be right even twice a day, since it runs slow even backwards.

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