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davidr41
01-13-2012, 07:10 PM
Hello All,

My name is David and I have recently purchased a propeller quickstart board from radioshack. I'm very new to microcontrollers, having only done a few programs involving lighting the 8 LEDs on the quiskstart board in various sequences, so I still have much to learn.

I've been thinking of practical projects that I might make using the propellor quickstart and one idea that came to mind was a program and set of sensors that can accurately sense level in 3 dimenions ie knowing when they are all 3 level to the ground relative to each other.

The application of the sensor system would be to determine easily when my telescope tripod was level on all 3 legs to the ground, which is important for properly aligning the telescope for viewing. My telescope tripod/mount, once properly leveled and aligned with the north star, will keep the telescope aligned with the earth's motion and allow you to view astronomical objects without them leaving the telescope's field of view due to the earth's motion. My best viewing location happens to be a sloped driveway and I always have a difficult time getting the tripod properly leveled. I've used bubble levels, but it always seems like such a chore.

Does anyone have any ideas of the type of sensors that I would need and whether this idea is possible? I am envisioning perhaps using a sensor for each leg and having one leg as a reference leg. The other two sensors would use LED strips to indicate when they are level relative to the reference led, if that makes any sense.

Thanks in advance for your ideas!

-David

Mike G
01-13-2012, 07:39 PM
Welcome to the forum, davidr41

Acceleration and Tilt sensors
http://www.parallax.com/Store/Sensors/AccelerationTilt/tabid/172/CategoryID/47/List/0/Level/a/SortField/0/Default.aspx

Duane Degn
01-13-2012, 07:39 PM
David,

Welcome to the forum.

I like your project idea. The first sensor that comes to my mind is an accelerometer (http://www.parallax.com/Store/Sensors/AccelerationTilt/tabid/172/CategoryID/47/List/0/SortField/0/Level/a/ProductID/585/Default.aspx). It will take a bit of math to figure out what angle it could detect with it's 10 bits or resolution. The 10-bits applies to an 8G reading so your down to 7-bits for a 1G reading. I think that's 1/127 G resolution. I think we want the arcsine of 1/127 to find the minimum angle detectable which is 0.45 degrees. So (if I did my math right), you'd be able to sense a variation from level to within 0.45 degrees. Is that good enough?

It would be nice if the legs automatically adjusted themselves, but maybe you can work that out after you have a way of sensing if your telescope is level or not.

Edit: I think I was incorrect about the 0.45 degree angle. The 7 bits covers +/- 1G a 2G range so we lose another bit. So the resolution is reduced to 0.9 degrees.

Phil Pilgrim (PhiPi)
01-13-2012, 07:49 PM
David,

Welcome to the forum!

Can I infer from your post that your telescope has an alt/az mount with some kind of computer-controlled tracking? With an equatorial mount, the tripod doesn't have to be level, so long as the equatorial axis points to the North Star. 'Just curious.

-Phil

Spiral_72
01-13-2012, 08:08 PM
If you rigid mount the sensor on the end of a vertical stick underneath the mounting surface of your EQ mount.... wouldn't you multiply the resolution according to the length of the stick?

I think that's right!


EDIT: As Duane pointed out - And if I may use a strong adjective: That's a dumb idea..... never mind :)

Duane Degn
01-13-2012, 08:19 PM
If you rigid mount the sensor on the end of a vertical stick underneath the mounting surface of your EQ mount.... wouldn't you multiply the resolution according to the length of the stick?

I think that's right!

Are you talking about an accelerometer as the sensor? Then, no the angle would stay the same.