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Wrist Diode-Dial

 Have a five o’clock shadow on your arm.
  (+14, -1)(+14, -1)
(+14, -1) 		  [vote for,
against]

This retro wristwatch would have no hands. Instead it would show the time by casting hour and minute shadows from a central, pointer, similar to a sundial. The light source would be two concentric rings of 24 diodes each, one over the other. The diode ring nearest the base would light, one-by-one, to cast a long, minute shadow. The upper ring would create a short, hour shadow. For example if the first upper diode and the third lower diode to the right of 12 were lit, the time would be about 6:37.

I found some references to electronic sundials on the net but without description or pictures.

—FarmerJohn, Jul 16 2002

wrist sundial http://colorsofindi...m/sundial/play.html
These, not using electronics, are quite baked [FarmerJohn, Jul 16 2002, last modified Oct 21 2004]

Wrist Diode-Dial sketch http://www.geocitie...nnie/diodedial.html
with thanks to beauxeault, wherever he may be [FarmerJohn, Oct 04 2004, last modified Oct 21 2004]

Solsuno LED Watch. http://www.thinkgee...dgets/watches/664e/
[ThinkGeek] LED coolness! [Letsbuildafort, Oct 04 2004, last modified Oct 21 2004]

Street Clock http://3eyes.co.uk/...ic/?doc=Streetclock
Public art sundial thingy. (Beware embedded .mov) [Acme, Jul 28 2005]

[link]






       For two LEDs at full brightness, that's going to be at least 20 mA current drain at 1.6 - 1.8 V. A typical CR2016 coin cell (Lithium Thionyl Chloride) used in many watches has an energy capacity of about 100 mAH, so it would run the watch (assuming the power drain for the timekeeping system is negligible) for about 5 hours.   

       I think the device is practicable - although it would be hard to read in direct sunlight - but would be limited by battery life.   

       NOW:   

       If you do the following:   

       1. The LEDs illuminate only on user command,   

       2. The "face" of the watch is a photovoltaic,   

       3. The watch incorporates a compass so that you can use it as a real sundial when you are outdoors and the sun is out,   

       then you might have something more practical for day to day use.   

       You could even use the sundial/compass combination to set the watch automatically to local time (except near the poles)   

       I really like this beacause it's a very good fit for the Hafbakery Mission Statement, and doesn't involve anyone getting splattered with hot fat and bits of charred sausage (bitter bitter bitter). Croissant.
—8th of 7, Jul 16 2002
   

       I thought of pressing a button for viewing the time. The combo with sundial was pretty well thought out until I saw that the latter was baked and would probably sink the idea.   

       Of course there are also difficulties such as isolating the compass from the battery's magnetic field, markings for 6 AM and 6 PM being where 9 and 3 are, varying hour intervals depending on latitude and different compasses and markings for northern and southern hemisheres.
—FarmerJohn, Jul 16 2002
   

       The 6AM/6PM thing is easy enough to handle if you have an LCD which can dynamically recalibrate; the Lat/Long is a bit more tricky unless you have GPS, in which case the sundial is a bit redundant as you get the time for free ....
—8th of 7, Jul 16 2002
   

       Can I get it in a granite finish? (Flintstones)
—Mr Burns, Jul 16 2002
   

       Sure, maybe you're also interested in a sandstone hourglass.
—FarmerJohn, Jul 16 2002
   

       Yup. Hook it up!
—Mr Burns, Jul 16 2002
   

       // a central pointer, similar to a sundial //
Am I picturing this correctly as a small pointy triangle jutting up from the back of my wrist? I see myself getting tired at work, dropping my head onto my folded arms on the desk for a quick nap, and going around the rest of my life with my left hand nailed to the bridge of my nose.
—hob, Jul 16 2002
   

       Well it's not a pyramid, more like a syringe . . . no maybe twice as tall as the axel for the hands on regular watch, covered by glass (crystal).
—FarmerJohn, Jul 16 2002
   

       Another cool watch could be made similar to this, with very flat ring of red diodes and a very flat ring of green diodes, one on top of the other, and a simple, thin, cylindrical post extending from the center of the watch face to the center of the glass that covers the face. If you used the red diodes for hours and the green ones for minutes, you'd have a white watch face with a red minute hand and a green hour hand. Except for when the hands overlapped, and then you'd have a single black (or gray) hand. The "hands" would really be thin wedges extending from the center post to the edge of the dial. You'd lose the sundial function, but I think it would look cool enough that it would actually sell. Too bad about the battery problem.
—beauxeault, Jul 16 2002
   

       Oh, with a crystal over it -- as in FarmerJohn's link, I see. Now I feel safer.   

       However, I don't see how this can work if the time is, say, 6:00 or 12:33. You'd be trying to cast two shadows in opposite directions; wouldn't the lights cancel out the shadows or at least make them extremely hard to see -- unless the lights are of different colors as beaux suggests, but I'd think this would be a pretty subtle effect unless you're in a dark room... (just call me Mr. Negativity)   

       (bliss - Thanks. I am, but I haven't been working since last year; not sure if I've had enough or not.)
—hob, Jul 16 2002
   

       beauxeault & hob: The colors would make a neat effect. Another, less sophisticated way to improve readability would be to show the hour shadow one second followed by the minute shadow.
—FarmerJohn, Jul 17 2002
   

       The problem is how to get a tan where the shadow is cast? Nice idea FJ.
—pashute, Nov 04 2002
   

       I like this concept: a wrist sundail which, unlike the "old" models, works even at night.
—supercat, Nov 04 2002
   

       Returning to the led current consumption, this can be drastically reduced by driving the leds with pulses of current, and adjusting the 'duty cycle' - the proportion of 'on' to 'off' time. Also, how about incorporating a mini solar cell array in the dial to help keep rechargable cells alive.
—viridens, Nov 20 2002
   

       I don't think you need the LEDs anyway. Lots of watches don't have lights. You just use them under streetlights, cigarette lighter, etc.   

       It wouldn't be even the slightest bit accurate for telling the time of course, but then if you wanted practicality and accuracy you'd buy a good digital for 20 bucks.
—Chippy, Jun 16 2003
   

       [Chippy] It's the shadows that the two lighted LEDs cast from the central pointer that are the watch's hour and minute hands. It would show the correct time within 2 1/2 minutes.
—FarmerJohn, Jun 16 2003
   

       ThinkGeek markets a watch with 138 colored LEDs on it. Going a step in your direction, anyway ... with linky too!
—Letsbuildafort, May 03 2004
   

       beauxeault: red and green light actually make a pleasing shade of yellow - not white. Maybe if you used red, green and blue for the hour/minutes/second hands.
—Macwarrior, May 03 2004
   

       LED watches are definitely baked, I'm wearing one now. It only lights up when I press a button, and lasts a year or two on ordinary watch batteries. Mine also adjusts brightness to light, so it can be seen in bright light without wasting excessive power in low light. So I think this idea is doable.
—Corona688, Jul 28 2005
   

       This is one of the better ideas on this site. I think, anyway. So plausible, too.
—bristolz, Feb 22 2006
   
      
[annotate]
   


 

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