Position sensing

cmartinez

Joined Jan 17, 2007
6,467
My memory was off. I thought it only came in 32 bit version; actually There is no 32 bit version. There's 12bit and 28 bit. yeah 12bit should be fine.
And now that I remember, the OP wanted a 1 mm resolution, more or less. With an ordinary 8-bit ADC he'd get a 1.2 mm resolution, which sounds like a reasonable compromise for his application. And it would be far easier to implement than any of the other resolutions available.
 

shortbus

Joined Sep 30, 2009
6,984
OK this has been bugging me, so had some time last night and did some research once the OP gave what he is really doing. There is such a thing being made and sold, though farms around here don't use or need them. It's called a "rising plate pasture meter". The way it has been described in the thread is backward to what and how they are made and used. http://jenquip.co.nz/categories/rising-plate-pasture-meters

Kmoffet's picture is pretty close to what the look like. They have a disc that floats on a shaft, NOT as the OP suggested a rod that drops through a tube. You would push the shaft down into the crop and the disc stays on top of the crop, thus measuring the height of the crop.

Now the how to from my point of view, sure you guys will have other ways of doing it.
1. A light weight disc with a hole in the middle, the hole has a bushing to make the disc stay level to the center shaft/pole. The store bought ones use thin aluminum, but thin plastic might work too.

2. A pole or shaft to allow the meter to be used without bending over. The pole needs to be a loose, sliding fit in the disc/bushing to allow free movement up and down the pole, real important to this working.

3. A flat length of light weight material, that is stiff enough to stand up right, and not transparent. This is attached to the disc, near the bushing, perpendicular to the disc and parallel to the pole. This would have holes drilled at repeating distances. The OP said 1mm resolution but think that's not necessary, 1cm would probably be close enough, we're measuring grass after all.

4. Now the actual measuring part. A opto interruptuer module. One with a slot to allow the part #3 to go through it. As the holes go past the light sensor it will count the number of cm's that the pole drops through the disc until it hits the earth. The opto interrupter will allow both free movement and keep the measuring stick from rotating.This count would then be given to what ever is used as a display or memory. Not even going to address that here. They even have the optos with a counting circuit built in, to use with a micro.

upload_2017-6-29_11-1-24.jpegupload_2017-6-29_11-3-29.jpeg
 
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Thread Starter

geoffers

Joined Oct 25, 2010
306
Thanks again all,
That's what I'm doing, however I clearly underestimated how much effort you guys are prepared to put in to help out!

I genuinely thought no one would be particularly interested in what the end result is , just the mechanics of how the measurement is made, so that was the question I asked :)

As for doing it on the cheap, well maybe the more affordable, £400 buys a basic one over here, you can add much more for Bluetooth and individual paddock recording, thanks mainly to guys here I can make a pic do quite a bit, for me to add Bluetooth would cost £6-7 + my time.
I'm sure you all understand why I would want to make my own anyway :)
Cheers Geoff
 

shortbus

Joined Sep 30, 2009
6,984
Thanks again all,
That's what I'm doing, however I clearly underestimated how much effort you guys are prepared to put in to help out!

I genuinely thought no one would be particularly interested in what the end result is , just the mechanics of how the measurement is made, so that was the question I asked :)

As for doing it on the cheap, well maybe the more affordable, £400 buys a basic one over here, you can add much more for Bluetooth and individual paddock recording, thanks mainly to guys here I can make a pic do quite a bit, for me to add Bluetooth would cost £6-7 + my time.
I'm sure you all understand why I would want to make my own anyway :)
Cheers Geoff
Many of us are retired and for myself been a 'problem solver' most of my life, this and other forums allow the brain to keep working. Though some would claim I have no brain, especially my wife, sometimes. Always trying to make something to do what an expensive "toy" can do. Never heard of one of these and had the time so started looking and found them and the name of them. Around here our farms are large, the stock just kind of regulates them selves, they go where the best grass is and let the cropped grass regrow on it's own.
 

Thread Starter

geoffers

Joined Oct 25, 2010
306
Well its most appreciated here, I nearly always find out more than I expect here. We have a farm a toddler and a 8 week old so time is pretty tight!
That's how we managed our grazing before, most of its still like that but after seeing a Irishman talk in the spring we changed the dairy cows to paddock grazing, the savings on bought in feed are surprising. Growing grass is a science now a days, its catching up to the way arable crops are managed :)
I will post my lash up here when its made!
Cheers Geoff
 

MrChips

Joined Oct 2, 2009
19,279
We're all shooting in the dark over this. If the TS would just tell us what he's trying to measure better ideas could be given. I'm assuming it's some kind of soil compaction measurement, but that's just an assumption, like all of the members trying to help are doing.

Please @geoffers, tell us what you are trying to do. Something like this goes through a design process in real life. With the first step being to give the statement of what is trying to be achieved. With that many of us can give better ideas about how to do the job needed. Keeping members in the dark because, it's secret or you want to make and sell it, is not something you need to worry about here. Most of us have our own interests and do this as a way to help others, not to 'steal' ideas.
I have stated this many times before and will continue to have to do so.
For all new members reading this thread, please be reminded of the importance of stating up front in the first post what you are attempting to do.

Give us the big picture from the start.

Without this information we are posting 100 suggestions all in the wrong direction.
 

MrChips

Joined Oct 2, 2009
19,279
Back to the problem.

Are you doing this manually, i.e. walking around the crop with a measuring stick in hand?
Or do you want to automate the process while you drive around the farm in your tractor?

If you are doing this manually, the measuring stick with the floating disc has to be longer than your highest crop, right?
Let us suppose that at the top of the stick you have a handle for manually holding the stick.
Put an ultrasonic range finder at the top end where the handle is located. Take a distance measurement using ultrasound reflected off the floating disc. Subtract this reading from the calibrated length and you will obtain your crop height.
 

shortbus

Joined Sep 30, 2009
6,984
Back to the problem.

Are you doing this manually, i.e. walking around the crop with a measuring stick in hand?
Or do you want to automate the process while you drive around the farm in your tractor?

If you are doing this manually, the measuring stick with the floating disc has to be longer than your highest crop, right?
Let us suppose that at the top of the stick you have a handle for manually holding the stick.
Put an ultrasonic range finder at the top end where the handle is located. Take a distance measurement using ultrasound reflected off the floating disc. Subtract this reading from the calibrated length and you will obtain your crop height.
This is why I said after the problem is truly defined, there will be other ideas on how to do it after mine. It all comes down to defining the problem in the first place, and not asking the members to guess what the problem is. :)
 

Thread Starter

geoffers

Joined Oct 25, 2010
306
Thanks,
Yep that's right, you walk the paddock's with the stick, dropping as you go, one of those laser range finder modules has arrived today so I will let you know how it goes!
The data sheet says it will work in daylight :)
Cheers Geoff
 
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