Detection of slow circular motion

[baruchli]

Hello,

I need to detect a position of wall clock hand by electronic located beyond clock face. I can think about next possibilities:

1. Hall effect sensors on clock round edge - magnet on clock hand tip - too expensive and bulky + magnet on clock hand will disturb its motion
2. Some grid on mechanics moving part connected to clock hand - will give me motion but not position + i need super sensitive photo element to distinguish motion of a small grid.
3. 3-axis accelerometer is overkill - I need only one axis + it whould be hard to read data from chip which is changing its angle relevant to other electronic units


Pot which moving part would be able to complete full round movement and would give me different analaogInput four each angle would be ideal.
Ladyada does such thing exist?
Does anybody has other ideas?

[adafruit_support_bill]

How about an optical encoder. They come in many styles. http://www.societyofrobots.com/sensors_encoder.shtml and can be found at many of the on-line robot vendor sites.

We have a pot-style 20 position rotary encoder in the store, but one of the encoder-wheel-style ones would likely be easier to adapt.

[meseta]

would it not be feasible to count the second ticks? You can add a sense wire into the wires that feed the coil in most (cheap) clocks.

[jwhance]

Might be beyond the capabilities of an AVR/Arduino chip but I'm sure you could use a camera, even a tiny/unobtrusive one, and take an image of the clock face. Since the only things in that image that should ever change are the positions of the hands, and they should be quite predictable, some realtively unsophisticated image processing should allow you to discern the hand positions.

My concern with the AVR is that you may not have enough memory (i.e. RAM) to store an image of high enough resolution to resolve the hands. You could always add an external RAM chip to your design if needed.

I think it would be in interesting project. I've not seen much on image processing in the Arduino space.