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I want to control an analogue clock movement with a microcontroller. A Lavet motor is used to advance the hands.

The issue is detecting where the hands are. I noticed that some radio controlled clocks move the hands to midnight before moving them to the correct time.

What mechanism do they use to detect midnight position?

user
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  • It could be any kind of sensor, it depends on gearbox. For example if gears are positioned on top, you could drill a small hole and use a LED and photo detector. – Marko Buršič Sep 30 '20 at 19:59
  • It would have to be extremely small to detect 1/60 positions. – user Sep 30 '20 at 20:16
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    Not necessarily, if you have multiple gears on top of each other. – Marko Buršič Sep 30 '20 at 20:21
  • @user all you need is one hole to identify the home position ... when the clock is set, then the controller would search for the home position and advance from there ... during normal operation, if the home position is not reached when expected, then an error is flagged – jsotola Oct 01 '20 at 00:28

3 Answers3

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According to this forum, it has a IR-LED detector and tiny hole.

enter image description here

Marko Buršič
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I know it's a little late, but I have been pondering the same thing, and searching the internet for ideas. Although what I was really looking for was validation of my own idea.

I have a cheap alarm clock that I bought for exactly this purpose. It operates from a 1.5V AA cell, and has a Lavet mechanism internally. My idea is to set the alarm to 12:00 and detect the alarm switch activation (which you can hear clicking on when you move the hands to 12:00).

So, once I disconnect the driver board from the coil and control the hands with an Arduino, I can detect 12:00 by monitoring the alarm switch. Therefore I know the hands are in a known position.

Probably cheaper and easier to find than the clock modules with optical sensors, albeit slightly less accurate at pinpointing 12:00 precisely.

Andrew
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I opened up a broken one and it is indeed an optical sensor. Sorry about the focus.

Sensor is the thing hanging over the top most cog.

enter image description here

user
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