motion sensor question

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I would like to put three LCD character displays into a long triangle shape like a Toblerone package. The display facing the viewer would display text. There would be thousands of messages stored on a serial EEPROM. The message displayed would change as the device was rotated.

I could stick the battery, the AVR, and the serial EEPROM in the center part of the triangle made up of three 24x2 LCD displays.

But how would I detect that the user has turned the device so that a new LCD display is facing them? Micro mercury switches? very cheap accelerometers?

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accelerometer sounds like the easiest way really

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Maybe a LED and a wheel with holes (like mices used to work).

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Is this on an axle, fixed mounted? Mount a knob encoder on the shaft. some of them have a "home" position.

You can put lipstick on a pig, but it is still a pig.

I've never met a pig I didn't like, as long as you have some salt and pepper.

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I guess it depends on the axis of rotation - a digital compass might work. (but only for rotation in the horizontal plane)

Or how about IR sensor and IR lights placed strategically around the room?

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accelerometer sounds like the easiest way really

...a digital compass might work.

Way too expensive. The final device with connectors and packaging can't sell for more than $20. That is the most of what people will pay for a novelty.

Is this on an axle, fixed mounted?

No, it would be a small hand-held item.

..LED and a wheel with holes

This would probably be close. Three low-power super-cheap IR LEDs and detectors arranged in a circle. There would be a center-mounted shaft with a metal flange. Gravity would pull the flange down to point to the ground as the unit was turned. The flange would shutter one LED/detector pair and that switch would update the LCD display that the user was viewing.

Thanks for the suggestions.

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I don't know how (in)expensive your IR detectors/LEDs are, but what about 3 pieces of copperclad arranged in a triangle with a small (tiny) ball bearing or metal bead rolling around inside. The bead will always short two planes together when it's held relatively horizontal. The conductive surfaces would be slightly concave to hold the ball, but if it's too far out of horizontal the ball rolls over into a nonconductive end cap.

You can determine by trial and error whether a slight tilt toward you (front/bottom shorted) or away from you (back/bottom shorted) activates which of the two upper faces.

(concave = etch a strip out of the middle. In fact, just use the two strips being shorted to detect the ball, not the sorting of two adjacent planes)

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Chuck Baird

"I wish I were dumber so I could be more certain about my opinions. It looks fun." -- Scott Adams

http://www.cbaird.org

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As I think about this a little more, you could etch a couple of identical pcbs as the endcaps, with three strips of copper arranged in a triangle. On each strip solder an el shaped piece of conductor so that one side sticks up off the surface of the pcb (the other side of the el is soldered to the copper strip). The side that sticks up is slightly wider than the diameter of the ball.

Put the two pcbs facing each other so the triangles line up, but with the protruding conductors not quite touching (closer together than the diameter of the ball). The ball is inside the resulting enclosed space. Done.

When the thing is held more or less horizontal, the ball will ride in the space between two rails and you can detect it. When it's way out of horizontal, the ball will be rolling around somewhere you don't care about, and you can shut the display down.

Attachment(s): 

Chuck Baird

"I wish I were dumber so I could be more certain about my opinions. It looks fun." -- Scott Adams

http://www.cbaird.org

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Is the device typically heald horizontal when in use?

If so, you can obviously expand upon Chuck's idea by making the plates in an Octagon shape, for example, to increase the resolution of detecting motion.

Scan the plates in a manner analogous to scanning a keypad, ( Make plate N high, measure Plate N+1 and Plate N-1, repeat for Plates 0-N...).

JC

Or connect the plates in series with resistors between them selected so that you can read the plate group with a voltage divider and an ADC and know which two plates are shorted. QED.

JC

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Quote:
Is the device typically heald horizontal when in use?

I was assuming it was, like when you're reciting last rites over a Toblerone package.

Chuck Baird

"I wish I were dumber so I could be more certain about my opinions. It looks fun." -- Scott Adams

http://www.cbaird.org

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Thank you for your replies. I'm a little to heat stroked to analyze them right now.

I'm thinking of having three sets of IR LED and IR LED detector pairs right next to each other. And a metal shutter on a shaft. When the device is held, the shutter will fall and point to the ground. The IR 'light' will reflect off it and be detected. The other two detectors will be 'dark' and not active. Maybe a standard visible light LED and detector would work better, but IR devices are cheap at about $0.16 each. I like cheap. The future is cheap.

Turning the reader device like a kaleidoscope will have the shutter always pointing downward. One pair of LED/detectors will always be on.

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Off Topic...

So Chuck, some day Microsoft's IE will actuall spell check for me...

By the way, a Toblerone isn't Leon's favorite new micro-development board with a USB interface and an HTTP stack. What it is can be found here: Wiki Toblerone

JC

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Quote:
a Toblerone isn't Leon's favorite new micro-development board

Thanks, but I'm all too well aware what a Toblerone is and am quite addicted to them. That's why when they get in my hands they need last rites.

And Firefox spell checks, so it's time to leave the dark side.

Chuck Baird

"I wish I were dumber so I could be more certain about my opinions. It looks fun." -- Scott Adams

http://www.cbaird.org

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By the way, Simonetta, although it appears that you have made up your mind on the approach to be taken don't be too quick to dismiss Chuck's idea.

It is possibly less expensive, and certainly provides a higher "turn resolution", and does so at a significantly lower current draw, (i.e. giving the ability to detect smaller amounts of motion, and making your batteries last longer).

JC

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Quote:
I'm thinking of having three sets of IR LED and IR LED detector pairs right next to each other.
Not knowing exact design of your gizmo.
But in my mind I see only ONE set of led-detector(you asked for cheap) and some sort of disc with 3 strategically placed holes mounted to the axis.
Turning the displays make led-detector packet pass one of the holes in the disc.